Posters

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Using archival data from the Chandra X-ray telescope, we measured the spatial extent of the hot interstellar gas in a sample of 49 nearby interacting galaxy pairs, mergers, and merger remnants. We compared the volume and mass of hot gas in these galaxies with their star formation rates, interstellar molecular and atomic hydrogen gas masses, and their infrared colors. Our results support the idea that stellar/supernovae feedback dominates the production of hot gas in these galaxies. The amount of feedback appears to depend upon the spatial density of young stars, the age of the stars, and/or the ratio of young to old stars

Co-Authors: Peter Wagstaff, Curtis Struck, Roberto Soria, Brianne Dunn, Douglas Swartz, Mark Giroux (East Tennessee State University, Iowa State University, University of the Chinese Academy of Sciences, Clemson University, NASA Marshall Space Flight Center, East Tennessee State University)

X-ray emission from young, low-mass, pre-main sequence stars is generated as a result of magnetic activity and the associated magnetic phenomena, such as coronal heating and magnetospheric accretion, are fundamental to the formation of stars. High resolution X-ray spectroscopy with Chandra-HETG offers a unique window to probe and distinguish the detailed physics underlying these processes. We present Chandra-HETG GTO observations of the nearby, pre-main sequence star SZ 96 which is a rare example of an accreting star-disk system at the cusp of disk dispersal. This system exhibits an unusual ∼9 day period in its optical light curve where it changes in brightness by 3-4 magnitudes in V band. This extreme optical variability may be related to the variability observed in X-rays over the course of roughly one ten day period. Here we present preliminary HETG results where we characterize the SZ 96 high resolution X-ray spectrum and its associated variability.

Co-Authors: Moritz Günther, Claude Canizares, Lucas Cieza, David Huenemoerder, Joel Kastner (MIT, MIT, Universidad Diego Portales, MIT, Rochester Institute of Technology)

The interstellar medium (ISM), gas and dust between stars, is an important constituent of galaxies, affecting star formation and their overall evolution. A powerful technique to study such environment is through X-ray observations because, due to their high energy, X-ray photons can trace simultaneously the cold, warm and hot phases of the ISM as well as the molecular and solid components. In this talk, I will first review the recent advances made on the analysis of the ISM using X-ray spectroscopy, including the development of 3D maps of the local multiphase ISM distribution as seen in X-rays. Such maps are crucial in the improvement of Galactic simulations. Then I will talk about exciting prospects for the future with the arrival of new X-ray missions.

Co-Authors: Javier A. García, Timothy R. Kallman (California Institute of Technology, NASA Goddard Space Flight Center)

The Chandra legacy project to obtain an extremely deep, high resolution gratings X-ray spectrum of the nearby early O star zeta Pup is now complete. A total of 881 ks of exposure time has been accumulated with the HETG gratings system and the ACIS detector on Chandra, yielding X-ray spectra 2-20 A with a resolution of 0.023 A (meg) and 0.012 A (heg). There are currently several focussed analysis projects underway with this unique dataset, which are briefly reviewed here. This poster discusses in detail the statistical analysis of the data in the time domain. Using 9 ks time slices of the observations, we have performed moment analyses, period search procedures, and rudimentary emission line fitting of these short time periods. We are able to characterize the zeta Pup dataset with statistical parameters in the time domain, describing the variability observed. A comparison to XMM data of zeta Pup is also presented.

Co-Authors: Y. Naze, J. Lauer, D. Huenemoerder, N. Miller, R. Ignace, and the zeta Pup Consortium (FNRS/U. Liege,Harvard & Smithsonian CfA,MIT,UWisc-Eau Claire,ETSU)

IRAS 09002-4732 is a poorly studied embedded cluster of stars in the Vela Molecular Ridge at a distance of 1.7 kpc. Deep observations with the Chandra X-ray Observatory, combined with existing optical and infrared surveys, produce a catalog of 441 probable pre-main sequence members of the region. The stellar spatial distribution has two components: most stars reside in a rich, compact, elliptical cluster, but a minority reside within a molecular filament several parsecs long that straddles the cluster. The filament has active distributed star formation with dozens of unclustered protostars. The cluster pre-main sequence population is <0.8 Myr old and deeply embedded; its most massive member is extremely young producing an ultracompact H II region. The cluster total population deduced from the X-ray luminosity function is surprisingly rich, twice that of the Orion Nebula Cluster. The cluster core is remarkably dense where strong N-body interactions should be occurring; its Initial Mass Function may be deficient in massive stars. We infer that IRAS 0900-4732 is a rare case where a rich cluster is forming today in a molecular filament, consistent with astrophysical models of cluster formation in clouds that involve the hierarchical formation and merging of groups in molecular filaments.

Co-Authors: Eric Feigelson, Michael Kuhn, Patrick Broos, Gordon Garmire (Pennsylvania State University, California Institute of Technology, Pennsylvania State University, Huntingdon Institute for X-ray Astronomy)

Our group is now engaged in the large Chandra project "Missing Link Clusters" to examine rich open stellar clusters aged 5-30 Myr that form a "missing link" in our understanding of evolution of pre-main-sequence stellar activity. Half of the proposed missing link clusters have already been observed by Chandra. Here, we report on the characterization of the cluster'membership, distances and ages, stellar X-ray and bolometric luminosities, and stellar masses employing Gaia, 2MASS, Spitzer, WISE and various ground-based optical-infrared photometric data. Preliminary mass-stratified activity-age relations in early stellar evolution for the combined sample of "missing link" and younger (<5 Myr) MYStIX and SFiNCs clusters are provided.

Co-Authors: Eric Feigelson, Michael Kuhn, Patrick Broos, Thomas Preibisch, Gordon Garmire (Pennsylvania State University, California Institute of Technology, Pennsylvania State University, Ludwig-Maximilians Universitaet, Huntingdon Institute for X-ray Astronomy)

Eta Carinae is the most luminous star within 3 kpc and most notorious for large-scale mass ejections like the kind that occurred in the mid-19th century. Despite its dramatic instability, its 2-10 keV X-ray emission varies in a reproducible way and is a major piece of evidence that the Eta Carinae is a massive, long-period binary system in an extremely eccentric orbit. X-rays originate from the shocked gas associated with a powerful wind-wind collision. We review X-ray monitoring observations starting in 1996 and continuing through 2020 using the NICER facility on the ISS. High resolution X-ray spectra from Chandra at selected phases provides unique information on the flow of the hot shocked gas and the structure of the wind-wind collision shock. We present new Chandra HETGS spectra in the context of earlier observations and describe plans for studying the system through periastron passage in February 2020.

Co-Authors: David Espinoza, Kenji Hamaguchi, Chris Russell, Ted Gull, Noel Richardson, Tony Moffat, Gerd Weigelt, Augusto Damineli (CUA, Pontificia Universidad Catolica de Chile, UMBC/NASA-GSFC, NASA-GSFC/STScI, ERAU, U. Montreal, MPIfR, IAUGSP)

The Orion Nebula Cluster (ONC) is an ideal astrophysical laboratory to study very young (<1-2 Myr) stars. Being the nearest site of massive star formation and hosting a rich low-mass, PMS stellar population, the core of the ONC is ideal for detailed spectroscopic studies of young embedded cluster stars. Because of its superb spectral and spatial resolution, this study of a massive embedded cluster can only be done with Chandra as no other observatory will have such capability for a very long time to come. Since its launch 20 years ago, Chandra observations of the ONC have been at the center of star formation studies. The Chandra Orion Ultradeep Project (COUP) established global X-ray properties of the stellar propulations with the ONC setting a true milestone in the X-ray studies of star forming regions. Further high resolution X-ray studies revealed unprecedented details about young stars at a wide mass range. For Cycle 21 a very large project observation with an exposure of 1650 ks was approved to harvest up to three dozen high resolution X-ray spectra from young massive, intermediate mass, and low mass stars to determine line widths, line ratios, and abundancea in the core of the ONC. In this review we highlight results from the observations made during the last 20 years of Chandra observations as well as present the science goals we anticipate to achive with the new exposure.

Maybe you thought carbon stars (with C/O>1) were all highly evolved, asymptotic giant branch (AGB) stars. Dwarf carbon (dC) stars are actually far more common than C giants and have accreted carbon-rich material from a former AGB companion, yielding a white dwarf (WD) and a dC star that has gained both significant mass and angular momentum. Some dC systems have undergone a planetary nebula phase, and some may evolve to become the more famous CH, CEMP, or Ba giants. Most dCs seem to be from older, metal-poor kinematic populations where perhaps it is easier to achieve C>O. Given the well-known anti-correlation of age and activity, dCs would thus not be expected to show significant X-ray emission related to coronal activity. However, accretion spin-up might be expected to rejuvenate magnetic dynamos in these post-mass-transfer binary systems. We describe our Chandra pilot study of six dCs selected from the SDSS for Halpha emission and/or a hot WD companion, to test whether their X-ray emission strength and spectral properties are consistent with a rejuvenated dynamo. We detect all six dCs in the sample, which have X-ray luminosities ranging from log Lx of 28.5 to 29.7, preliminary evidence that dCs may be active at a level consistent with stars that have short rotation periods of several days or less. We describe further, upcoming Chandra observations that should help determine the amount of accreted mass and provide constraints for simulations.

Co-Authors: Paul J. Green(1) , Rodolfo Montez(1) , Fernando Mazzoni(2), JosephFilippazzo(3), Scott F. Anderson(4), Orsola De Marco(5),Jeremy J. Drake(1) , Jay Farihi(6) , Adam Frank(7), Joel H. Kastner(8),Brent Miszalski(9), and Benjamin R. Roulston(10) (1 Harvard Smithsonian Center for Astrophysics2 University of Massachusetts, Lowell3 Space Telescope Science Institute4 University of Washington, Seattle5 Macquarie University6 University College London7 University of Rochester8 Rochester Institute of Technology9 South African Astronomical Observatory10 Boston University)

Observations by the Chandra X-ray Observatory provided unambiguous evidence for the existence of hot bubbles embedded in planetary nebulae (PNe). Hot bubbles were a key prediction of the interacting wind theory and Chandra's high spatial resolution, low-background, and sensitivity to soft X-ray photons allowed for their identification. After a few more detections, it became clear that the hot bubbles were not measuring up to their prediction. Specifically, the hot bubbles were simply not hot enough. This discrepancy between theory and observations sparked the Chandra Planetary Nebulae Survey (ChanPlaNS), a multi-cycle, multi-institutional effort to observe all known planetary nebulae within 1.5 kpc of the Sun. In this presentation, we highlight many the discoveries made from the suite of Chandra observations of PNe, including hot bubble physics and unexpected features of the central stars. We also frame the potential for future observations by Chandra and future missions.

Co-Authors: ChanPlaNS Team (0.0)

Cepheids are variable pulsating stars with pulsating stars with well known disturbances in the photosphere and chromosphere at minimum radius as the pulsation compression passes through. Recently, an X-ray variable signal was captured in observations during the maximum radius phase indicating an X-ray source located higher in the Cepheid atmosphere. This variable X-ray emission was unexpected and there has not been any theory proposed as of yet that can explain the details of these observations. In this work we explore the possibility of shocks being the responsible mechanism for the observed X-ray variability. For that, we use a modern 3D MHD code to simulate the Cepheid variability and assess the capability of pulsation-driven shocks to create a phase-dependent X-ray luminosity enhancement in these stars. Finally we synthesize X-ray light curves to evaluate the heating efficiency of this mechanism and link our simulations to observables. We find that under specific conditions shocks are able to reproduce a phase dependent X-ray luminosity enhancement for pulsation driven outflow and discuss the implications of such a scenario on the Cepheid atmospheres and their mass loss.

Co-Authors: S. P. Moschou [1], N. Vlahakis [2], J. J. Drake [1], N. Evans [1], J H. Neilson [3], J. A. Guzik [4] ([1] Center for Astrophysics | Harvard & Smithsonian, USA,[2] University of Athens, Greece,[3] University of Toronto, Canada,[4] Los Alamos National Laboratory, USA)

Massive star formation has now become a major focus in astrophysical research. It occurs inside dense, compact clumps in giant molecular clouds with molecular hydrogen column densities exceeding 10²³ cm^-2. As a consequence of the initial mass function (IMF), high mass stars are rare and generally at great distances from the solar system. This complicates the study of these objects. Although these newly formed high mass stars embedded in compact cores of warm dust and molecular gas are responsible for the creation of hyper- and ultra-compact HII regions, methanol masers have also been established as exclusive tracers of high mass star formation. These methanol masers have high brightness temperatures that enable us to probe smaller scale structure that would not be possible otherwise.

Roughly two decades ago the monitoring of methanol masers towards a sample of IRAS point sources with the 26 m Hartebeesthoek radio telescope, resulted in the discovery of periodic/regular variability of the maser flux density. Several hypotheses have been made to explain this peculiar behaviour. Here the hypothesis and results of the scenario of the colliding wind binary model is presented. The colliding wind binary attributes the periodicity to the period of a binary system. There are a well known sample of colliding wind binaries available. One of the questions is, what about their progenitors? There should be a sample of binary systems in the early stages of high mass star formation, how will we be able to identify them? From the production of X-rays in the hot shocked gas of the collision of these binary stellar winds, the detection of X-rays from these sources would give merit to establish the presence of binary systems in high mass star formation. I will present theoretical predictions of the possible detection of the presence of binary systems in these sources with Chandra.

Co-Authors: Johan van der Walt, Melvin Hoare, Julian Pittard (North West University, University of Leeds)

For more than a decade, the High-Resolution Camera on Chandra has been imaging α Centauri AB (G2V+K1V) – central pair of the famous close-by triple system – to follow coronal (T∼1 MK) variations of the two sunlike stars, produced by analogs of the 11-year solar activity cycle. A few years ago, Procyon (F5IV-V) was added to the long-term effort. Very recently, four new dwarfs – ξ Bootis AB (G8V+K4V) and 70 Ophiuchi AB (K0V+K5V) were approved in Chandra Cycle 21, for a three-year pilot program. Coronal periods of 20 yr and 8 yr are indicated for α Cen A and B, respectively. Considering also the Sun's contemporary cycle, the X-ray amplitudes (MAX/MIN) are large: several to ten. Procyon, in contrast, has shown only a smooth, modest decline over the past nearly 20 yr (including previous archival X-ray pointings), possibly consistent simply with long-term instrumental degradation, but puzzling nonetheless given the large-contrast cycles of the other dwarfs. Procyon, α Cen AB, and the Sun all have similar rotation periods, but different surface temperatures, gravities, ages, and metallicities (Procyon is younger than α Cen or the Sun; α Cen is metal-rich compared with the Sun and Procyon); which potentially can inform theoretical explorations of Dynamo magnetic cycling in cool stars. As a side benefit, the long-term sequence of Chandra observations of α Cen has captured about a dozen serendipitous X-ray sources in the central 17'×17'of the HRC field. Most of these are highly variable, flaring in a few of the frames, absent in the others. The transient nature of the X-ray field around α Cen – in the Galactic plane dominated by nearby stars – emphasizes the importance of the time domain for recording the high-energy stellar sky.

The Small Magellanic Cloud (SMC) contains an active population of X-ray pulsars with spin periods ranging from seconds to kiloseconds. Being located at a known distance and due to low foreground absorption, the SMC serves as a unique laboratory for studying the evolution of X-ray binaries. A comprehensive archive of data from Chandra(346), RXTE(952), XMM-Newton(167), and NuSTAR(38) observations of SMC X-Ray pulsars was created, consisting of all observations from first light to the present. This library serves as a resource for scientific data products, i.e, temporal, physical, and statistical properties pertaining to ∼70 X-ray emitting binary systems in the SMC. The products that our pipeline produces include: spin periods, light curves, source specific event files, periodograms and X-ray spectra. Comprehensive time-evolving sequences of spin periods, pulse amplitudes, pulsed fractions and X-ray luminosities have been generated from Chandra, XMM-Newton and NuSTAR data. Future plans also include incorporating NICER, Suzaku, and Swift observations into the library. A public release of this library is planned soon in order to enable other researchers to use these data products for modelling purposes and for probing the physics of accretion processes and neutron star magnetospheres.

Co-Authors: Sayantan Bhattacharya, Rigel Cappallo, Silas G.T. Laycock, Dimitris M. Christodoulou (University of Massachusetts Lowell)

We report on the initial results from high resolution dispersed spectroscopic studies of SN 1987A, based on our new deep (340 ks) Chandra HETG observation (taken in March 2018). Our preliminary analysis shows that the K-α to Ly-α line flux ratios for several ions have considerably decreased (e.g., by ∼40% for Si and Mg lines) between 2011 and 2018. Three dimensional hydrodynamic simulations that self-consistently reproduce the line profile features from March 2011 observation, seem to underestimate the increase of Ly-α flux compared to our corresponding observations in March 2018. Our initial results from the spectral model fits to the broadband 1st order dispersed spectrum of SN 1987A indicate significant changes in the thermal condition of its X-ray emitting hot gas. We observe that the temperature trend for the bimodal components from 2004-2011 seems to have changed in March 2018 with the soft and hard component temperatures increasing by ∼15% and ∼25% respectively, compared to their 2011 counterparts. We discuss this spectral evolution in comparisons with our synthetic spectra for quantifying various assumptions on the shock evolution through the interactions with the inner ring, ejecta, and beyond.

Co-Authors: Sangwook Park, Marco Miceli, Salvatore Orlando, Svetozar A. Zhekov, Kari A. Frank, David N. Burrows (University of Texas at Arlington, Dipartimento di Fisica e Chimica Università degli Studi di Palermo, INAF-Osservatorio Astronomico di Palermo, Institute of Astronomy and National Astronomical Observatory Sofia, Northwestern University Technological Institute, Pennsylvania State University)

The mass loss history of massive stars is one of the least understood yet fundamental aspects of stellar evolution. HOW and WHEN do massive stars shed their envelopes? Is there a relationship between the expulsion of the stellar envelope and core collapse? Is there a fundamental relationship between late time mass loss and supernova classification? Here we present results from a recent Chandra program to study the mass loss history of massive stars. SN 2003gk, located 40 Mpc away, is a Type Ic SN which lost all of its hydrogen, and much of its helium envelope, prior to core collapse. Recent Chandra observations suggest that the blastwave has caught up with that ejected material, and the supernova is now strongly interacting with circumstellar interaction. This places this unique object in the growing class of stripped envelope supernovae which show late time interaction, such as SN 2014C and SN 2001em. We discuss these new results and place them in context with Galactic and Magellanic Cloud supernova remnants which are thought to arise from stripped progenitors.

Co-Authors: Dan Milisavljevic, Raffaella Margutti (Purdue University, Northwestern University)

Investigating the interstellar gas associated with a supernova remnant (SNR) is important in understanding the origins of both the thermal and non-thermal X-rays, via shock ionization and magnetic field amplification. N63A is one of the X-ray brightest SNRs in the Large Magellanic Cloud, whose size is 81" × 67" (diameter of ∼18 pc at a distance of 50 kpc). The SNR contains an optical nebula (diameter of ∼6 pc) within the shell, which shows evidence of shocked molecular material based on its near-infrared colors. Using ALMA data, we spatially resolved clumpy molecular clouds embedded within the optical nebula, suggesting that part of the molecular clouds are ionized by shocks. The Chandra X-ray spectrum toward the gas clumps can be explained by either an absorbed power-law model or a high-temperature plasma model, in addition to thermal plasma components, implying that the shock-cloud interaction may produce both shock ionization and magnetic field amplification. In this talk, we will also report a brief summary of our ALMA and Chandra studies of the Magellanic SNRs in addition to specific results in N63A.

Co-Authors: Yumiko Yamane^1, Hideaki Matsumura^2, Kazuki Tokuda^{3,4}, Miroslav D. Filipovic^5, Gavin Rowell^6, Manami Sasaki^7, Paul P. Plucinsky^8, Kengo Tachihara^1, Yasuo Fukui^1 (Nagoya University^1, The University of Tokyo^2, Osaka Prefecture University^3, NAOJ^4, Western Sydney University^5, The University of Adelaide^6, Friedrich-Alexander-Universitat Erlangen-Nurnberg^7, CfA^8)

As demonstrated by Chandra and other recent X-ray observatories, a high-resolution X-ray spectroscopy is a valuable tool for plasma diagnostics of astronomical objects. Observations of the Perseus cluster with Hitomi (Hitomi Collaboration et al. 2016, 2017) indicate one of those important aspects. Supernova remnants (SNRs) are other intriguing targets for the high-resolution spectroscopy since they are usually dominated by thermal (non) equilibrium plasmas, especially when they are in an evolved stage. Although the planned X-ray Calorimeters on XRISM and Athena are promising for near future X-ray studies of any extended targets, a grating spectrometer is still useful for not only point sources but also less extended sources such as LMC/SMC SNRs. We here report on our high-resolution spectral analyses of SNRs with Reflection Grating Spectrometer (RGS) onboard XMM-Newton. From our RGS observation of a nearby middle-aged SNR, the Cygnus Loop, we discovered a high forbidden-to-resonance line ratio of OVII Heα from a southwestern rim (Uchida et al. 2019). The target is a compact knotty structure located at the outer edge of the shell, where the blast wave is likely interacting with dense surrounding materials. Investigating several possibilities that may enhance the forbidden line, we found that a charge exchange (CX) model (with a shock-heated ISM obscured by neutral and ionized absorbers) can explain the whole spectral feature including OVII Heα. This would be the most robust evidence for the CX process found in SNRs. We also report on an RGS observation of N49, which is one of the brightest SNRs in the LMC. As is the case with the Cygnus Loop, we detected relatively strong forbidden line of OVII compared with the resonance line from N49 (Amano et al., in prep.). We however ruled out the possibility of CX X-ray emission in case of N49 since the CX model cannot reproduce several Fe-L shell lines. The whole spectral feature suggests the possibility of another process, resonance scattering (RS), which selectively reduces the resonance line intensity and enhance the forbidden-to-resonance line ratio of OVII. While both CX and RS have not been considered in current standard analyses of SNRs, these newly-recognized processes will become one of major research topics for the near future missions such as XRISM and Athena.

Co-Authors: Satoru Katsuda, Yuki Amano, Hiroshi Tsunemi, Koji Mori, Liyi Gu, Renata S. Cumbee, Robert Petre, and Takaaki Tanaka (Saitama University, Kyoto University, Osaka University, Miyazaki University, RIKEN, SRON, University of Georgia, NASA/GSFC)

Massive stars often lose most of their H (and even He) envelopes prior to their explosions, through processes that are still poorly understood. Explosions of such stripped stellar cores produce supernovae (SNe) Ibc and IIL/b. Cas A, the youngest-known core-collapse (CC) Galactic supernova remnant (SNR), was produced by an SN IIb, but there are several other young remnants of stripped-envelope explosions known in our Galaxy. Among them, 1700-yr old RCW 89 (MSH 15-52) and 3000-yr old G292.0+1.8 stand out by having their X-ray spectra strongly dominated by clumpy heavy-element SN ejecta, in this respect making them like Cas A. RCW 89 has been inferred to be of Type Ib/c, while G292.0+1.8 is likely of Type IIL/b. We can learn much about origins of stripped-envelope SNe by studying their remnants with Chandra.

We present multi-epoch Chandra observations of RCW 89 and G292.0+1.8, spanning time baselines more than a decade long, that directly reveal fast expansion of clumpy SN ejecta in both remnants. In G292.0+1.8, outlying ejecta knots move radially away from the SN explosion site. In the south, we find that these ejecta are moving particularly fast, with an average expansion of 0.032% per yr and with speeds up to at least 2500 km/s, nearly as fast as the optically-emitting ejecta. These ejecta are in nearly free expansion. In RCW 89, we find compact Ne- and Mg-rich ejecta knots moving with speeds up to nearly 5000 km/s. They also move radially away from the remnant's center, but they have suffered significant deceleration, unlike the outlying ejecta in G292.0+1.8. Unexpectedly for a 1700-yr old remnant, we found RCW 89 to be an extraordinarily dynamic object that shows evidence for brightness variations by up to a factor of a few and profound morphological changes. Entirely new compact emission knots appeared in 2018, while several other knots faded considerably in the last decade. Quite a few fast-moving, compact ejecta knots appear to have shown significant morphological changes.

We also report on our expansion measurements of the blast wave in G292.0+1.8, and on our discovery of the long-sought primary blast wave of MSH 15-52 + RCW 89 that is expanding into denser than average ambient gas north/northwest of the centrally-located pulsar. Blast wave speeds vary by at least a factor of 2 in both remnants. Very fast (up to several thousand km/s) shocks are present in RCW 89. The fastest shocks exhibit pure nonthermal X-ray synchrotron spectra, without any lines present.

We discuss G292.0+1.8 and RCW 89 in the context of other stripped-envelope SNRs. This includes G330.2+1.0 that was recently found to be less than 1000 yr old, hence intermediate in age between Cas A and these two remnants. Synchrotron X-rays might be more efficiently produced in remnants of SNe Ibc. We also discuss fast shocks that we found in RCW 89 in context of several other X-ray synchrotron dominated shell SNRs. This includes G310.6-1.6, an enigmatic small-diameter CC remnant, and the youngest Galactic SNR G1.9+0.3 that Chandra has now observed over a decade-long time baseline. In all these cases, the sub arcsecond capability of Chandra has provided results inaccessible by any other means.

Co-Authors: William A. Miltich, Stephen P. Reynolds (North Carolina State University)

Despite decades of intense efforts, many fundamental aspects of Type Ia supernovae (SNe Ia) remain elusive. X-ray measurements of the element distributions in supernova remnants (SNRs) offer the key to understanding the explosion mechanism for SNe Ia. Here we present deep Chandra observations of G344.7-0.1, a middle-aged SN Ia remnant on the Galactic plane. The age of this SNR (3000-6000 yr; Combi et al. 2010, Giacani et al. 2011) is sufficiently large for all of the ejecta to have been shock-heated, thus becoming visible in X-rays. Moreover, these ejecta are still hot enough to emit strong Fe K lines (Yamaguchi et al. 2012), in contrast to other evolved SNRs, like G299.2-2.9 and DEM L71 (Park et al. 2007; Hughes et al. 2003). Thanks to this uniqueness, G344.7-0.1 is an ideal object for investigating the ejecta distribution in the entire SNR.

We performed ACIS-I observations of this SNR with a total exposure of ∼210 ks. The X-ray images show a centrally-peaked distribution of the Fe ejecta, surrounded by an arc-like structure of intermediate-mass elements (IMEs: Si, S, Ar Ca). Moreover, the centroid energy of the Fe K emission is significantly lower in the central Fe-rich region than in the outer IME-rich regions, suggesting that the Fe ejecta were heated by the reverse shock more recently. These results are consistent with a prediction of standard SN Ia models, where the heavier elements are synthesized in the interior of an exploding white dwarf. We find, however, that the peak location of the Fe K emission is slightly offset to the west with respect to the geometric center of the SNR. This apparent asymmetry is likely due to the inhomogeneous density distribution of the ambient medium, confirmed by our radio observations.

Co-Authors: Hiroya Yamaguchi, Patrick Slane, Sangwook Park, Plucinsky Paul, Satoru Katsuda, Hidetoshi Sano, Shogo B. Kobayashi, Kyoko Matsushita (ISAS/JAXA, Harvard-Smithsonian Center for Astrophysics, University of Texas at Arlington, Harvard-Smithsonian Center for Astrophysics, Saitama University, Nagoya University, Tokyo University of Science, Tokyo University of Science)

N132D is the most X-ray luminous supernova remnant (SNR) in the Local Group with a luminosity of L_x (0.3-10.0 keV) = 1.0e38 ergs/s. Given its location in the Large Magellanic Cloud, it is a prime target for detailed X-ray studies with the Chandra X-ray Observatory. The existing 87 ks Chandra observation of N132D has revealed the complicated spatial and spectral structure of this SNR, but the depth of this observation limits the spatial scale on which detailed spectroscopy may be performed. We successfully proposed for a Chandra legacy observation (900 ks) of N132D that will permit an unprecedented look at the spatial distribution of iron and other heavy elements in the ejecta from this prototypical core-collapse supernova. Combined with supporting multiwavelength data (from radio to gamma rays), these data will inform many areas of active research, including late stages of massive star evolution, explosion mechanisms and dynamics, and physical mechanisms for the interaction of shocks with molecular clouds and cavities. Observations such as this one provide a unique and important way to constrain models of massive stars and the supernovae they produce. Our observational program has begun and it will take approximately a year to collect the full exposure of 900 ks. We will present preliminary results from the observations performed to date.

Co-Authors: The Chandra N132D Legacy Team (SAO, JHU, NASA/GSFC, JAXA/ISAS, U. of Erlangen-Nuremberg, U. of Washington, U. of Nagoya)

Black holes (BHs) in dwarf/bulgeless galaxies play a crucial role in studying the co-evolution of galaxies and their central BHs. Identifying massive BHs in dwarf galaxies suggests that the growth of BHs could precede that of galaxies. However, some of the most intriguing candidate active galactic nuclei (AGN) in small galaxies have such low luminosities that the sample is vulnerable to contamination by other sources, such as supernova remnants. Reines et al. (2011) compared the X-ray and radio emission of Henize 2-10, a dwarf galaxy with a total stellar mass of ∼10¹⁰ M_⊙ (Nguyen et al. 2014), and argued that the X-ray and radio luminosities, and their ratio, excluded origins other than an AGN. Using the Fundamental Plane of BH activity, they claimed that Henize 2-10 hosts a central BH of mass M_BH ∼2×10⁶ M_⊙. However, deeper Chandra X-ray Observatory observations revealed that most of the X-ray luminosity was from an off-nuclear source, a likely high-mass X-ray binary (Reines et al. 2016). The weaker X-ray source coincident with the radio source had an X-ray luminosity L_{0.3-10 keV}∼10³⁸ erg s^-1. Reines et al. (2016) fit the X-ray spectrum of the nuclear source with a power-law and a thermal plasma model (APEC), but their spectral fitting did not discriminate between the models. A recent analysis of the MUSE optical IFU spectroscopy of the region by Cresci et al. (2017) did not detect any signs of AGN ionization. We re-analyzed Chandra observations of candidate AGN in Henize 2-10, considering the potential signals of emission lines in the minimally binned X-ray spectra. We identify clear signals of X-ray lines in the faint X-ray source identified with the radio source in Henize 2-10 by Reines et al. (2016). We find that hot plasma models, which are typical of supernova remnants, explain the observed spectra much better than simple power-law models, which are appropriate for AGN. Combining our work with the MUSE measurement of the ionization parameter in this region by Cresci et al. (2017) indicates that this radio and X-ray source is more likely a supernova remnant than an AGN. Our results indicate that investigation of X-ray spectra, even in a low-count regime, can be a crucial tool to identify thermally dominated supernova remnants among AGN candidates, and more generally, to separate line-dominated from continuum X-ray emission.

Co-Authors: Craig O. Heinke, Gregory R. Sivakoff, Aarran W. Shaw (University of Alberta)

Tycho's supernova is known to be a standard type Ia explosion based on the X-ray spectroscopy (Badenes et al. 2006) and on the observations of light echoes (Rest et al. 2008; Krause et al. 2008). The environment of supernova remnants, e.g., ambient density structure, is the key to obtaining information on the nature of the progenitor systems. We here report on our imaging analysis of Chandra data of Tycho's supernova remnant, aiming to constrain its progenitor system. By comparing Chandra ACIS images taken in 2003, 2007, 2009, and 2015, we estimated the velocity of the blast waves at various locations of the remnant, and found roughly consistent results with those of a similar analysis by Williams et al. (2016). We further searched for time variability of the velocity, and discovered that the blast waves are being substantially decelerated, particularly in the western and southern parts of the remnant. The deceleration observed in a wide range of azimuth angles would be difficult to be interpreted as a result of interactions between the blast wave and localized dense gas. Instead, our result can be well explained if the blast wave hit a gas structure like a cavity wall. To test this scenario and quantitatively discuss it, we performed a hydrodynamical simulation, assuming that the remnant is surrounded by a cavity wall. We found that the simulation is consistent with the observed data if the dense gas wall has ∼300 times larger density than the cavity and if the blast wave hit the wall ∼10 years ago or so. Our conclusion is supported also by CO line observations by Zhou et al. (2016), who found a expanding molecular bubble surrounding Tycho's supernova remnant. Such a bubble would be ascribed to a result of activities of the progenitor system rather than simply to natal molecular clouds. To constrain the nature of the progenitor system, we discuss possible mechanisms to form the gas structure, including the strong winds from a mass-accreting white dwarf proposed by Hachisu et al. (1996). We also discuss consistency with other observational results such as those by Woods et al. (2017).

Co-Authors: Takaaki Tanaka, Tomoyuki Okuno, Hiroyuki Uchida, Shiu-Hang Lee, Keiichi Maeda, Hiroya Yamaguchi (Kyoto University, Kyoto University, Kyoto University, Kyoto University, Kyoto University, ISAS/JAXA)

The ejecta motion in a supernova remnant (SNR) is one of the important clues to the origin of its supernova (SN). To measure it, we need to focus on not only the angular but also the line-of-sight direction at the target. Thanks for the excellent angular and energy resolution of Chandra, we successfuly measure in detail the Dopplervelocity of Fe ejecta clumps in Kepler’s SNR (∼2,000-3,000 km/s) and reveal the asymmetric expansion structure (Kasuga et al. 2018). We also analyze Tycho's SNR with the same procedure, and found that Tycho shows symmetricity in contrast. Such a difference could be due to the diversity of the mechanism or origin of type Ia SNe.

Co-Authors: Toshiki Sato, Koji Mori, Hiroya Yamaguchi, Aya Bamba (RIKEN , NASA/GSFC, University of Maryland, University of Miyazaki, ISAS/JAXA, The University of Tokyo, RESCEU)

Supernova remnants (SNRs) offer the means to study supernovae (SNe) long after the original explosion and provide a unique insight into the mechanism that governs these energetic events. In particular, the deviations from spherical symmetry observed in many SNRs can be compared to predictions from recent 3D simulations to further our understanding of SN physics. X-ray observations are crucial to probe the ejecta metals synthesized in explosions, and Chandra has yielded exquisite data that reveal these explosion asymmetries in detail. In this talk, I will discuss the X-ray morphologies of Milky Way SNRs and how the observed asymmetries of different ejecta metals are related to neutron star kick velocities obtained via proper motions from Chandra observations. Our findings show that NSs are preferentially kicked in a direction opposed to the motion of bulk ejecta. Furthermore, we find that in Cassiopeia A, the NS is kicked in a direction most opposite to the heaviest elements (e.g., Ar, Ca, Fe, Ti), and these heavier elements exhibit more asymmetric morphologies than lighter elements (e.g., O, Si, S). These results are consistent with the theory that NS kicks arise from conservation of momentum with asymmetric ejecta rather than with anisotropic neutrino emission, through a process commonly referred to as the gravitational tugboat mechanism. In the future, X-ray microcalorimeters will be revolutionary for SNR science, revealing the three-dimensional distribution of ejecta metals for direct comparison to hydrodynamical simulations.

Co-Authors: Laura Lopez, Katie Auchettl (The Ohio State University, DARK Niels Bohr Institute)

X-ray emission is one of the signposts of circumstellar interaction in supernovae (SNe), but till recently had been observed only in core-collapse SNe. The absence of X-ray emission from Type Ia SNe has been interpreted as a sign of a very low density CSM. Here we report late-time X-ray detections of SN 2012ca in Chandra data. The presence of hydrogen in the initial spectrum led to a classification of Type Ia-CSM, ostensibly making it the first SN Ia detected with X-rays. Our analysis of the X-ray data favours an asymmetric medium, with a high-density component which supplies the X-ray emission. The data suggest a number density >10⁸ cm^-3 in the higher density medium, consistent with the large observed Balmer decrement if it arises from collisional excitation. Although high compared to most core-collapse SNe, it may be consistent with densities suggested for some Type IIn or superluminous SNe. If SN 2012ca is a thermonuclear SN, the large CSM density could imply clumps in the wind, or a dense torus or disc, consistent with the single-degenerate channel. Another possibility is a core-degenerate channel, involving a white dwarf merging with the degenerate core of an asymptotic giant branch star shortly before explosion, leading to a common envelope around the SN.

Co-Authors: Chris Bochenek, Jeff Silverman, Ori Fox, Roger Chevalier, Nathan Smith, Alexei Filippenko (Caltech, Texas Austin/Samba TV, STScI, Univ of Virginia, Steward Observatory, Berkeley)

We have analyzed the archival Chandra X-ray Observatory observations of the compact feature in the Small Magellanic Cloud supernova remnant (SNR) 1E 0102.2-7219 which has recently been suggested to be the Central Compact Object remaining after the supernova explosion. In our analysis, we have used appropriate, time-dependent responses for each of the archival observations and we have modeled the background instead of subtracting the background. We fit unbinned spectra and use the C-statistic to evaluate the quality of fit. We find that the blackbody model is rejected at the 90% confidence level. The spectrum is described adequately by a non-equilibrium ionization model similar to other regions in the SNR which are dominated by ejecta heated by the reverse shock. Based on an MCMC analysis, the abundances of O and Ne are significantly enhanced compared to typical SMC abundances, but the the abundances of Mg, Si, S, are not constrained well enough to determine an enhancement.

Co-Authors: Terrance J. Gaetz, Paul P. Plucinsky (Harvard-Smithsonian Center for Astrophysics)

We investigate the potential for small satellites to observe exoplanet transits in X-rays and perform atmospheric transmission spectroscopy. The evolution of planetary atmospheres is one of the most uncertain aspects of exoplanetary astrophysics, with atmospheric loss rates being one of the primary uncertainties. Analogous to techniques applied in the ultraviolet, X-ray transit observations have the potential to study the atmospheric and escaping gas against the stellar coronal background emission. Here, we show that X-ray transit observations of close-in gas giants are detectable in repeated observations by an X-ray satellite with quite modest size and effective area. Such observations could provide powerful diagnostics of atmospheric scale heights, outflows and chemical compositions.

Co-Authors: J.J. Drake, V. Kashyap, S. Wolk, S. Romaine, C. Moore, K. Poppenhager, B. Wargelin, E. Winston, M. Elvis, I. Pilliteri (0.0)

The time available for planet formation is limited by the lifetime of the protoplanetary disks found around very young stars. The disk lifetime can be measured in young stellar clusters by counting the number of disk-bearing and disk-less stars for clusters of different ages. The conventional answer is that half of all stars have already lost their disks after 2Myr; however, there is some speculation that this is underestimated due to selection effects. We present initial analysis of a portion of the star-forming region IC 1396 just west of the Elephant's Trunk Nebula observed with XMM-Newton. We present cluster member identifications based on X-ray activity and Gaia astrometry, and show preliminary spectral energy distributions for these members.

Co-Authors: Moritz Gunther, Scott Wolk, J. Serena Kim (MIT Kavli Institute, Smithsonian Astrophysical Observatory, Steward Observatory)

During the past twenty five years, astronomers have established that most stars with masses comparable to or less than that of the Sun host planetary systems. Several intriguing gaps in our knowledge remain however. One of these is the frequency and characteristics of planets orbiting stars of higher mass. Another is the fate of planetary systems during and after the evolution of their stars. For example, few planets are known to orbit stellar remnants. Fortunately, the superb capabilities of Chandra mean that the data we have collected during the past twenty years can be used to discover planets in X-ray binaries. Determining the numbers and characteristics of such planets would help to answer both sets of open questions. The trick is simply that the X-ray-emitting regions in many X-Ray binaries are small enough that they can be totally eclipsed by planets. We report on intriguing results of our search through archived Chandra data for planets orbiting X-ray binaries.

We present the results of an analysis of both the point source population and the diffuse emission in the central regions of NGC 5128, which hosts the nearest radio-loud active galaxy, Centaurus A. We have used the full set of all archival Chandra ACIS + LETGS observations of Centaurus A to create the largest point source population list to date, and we also present spectral properties and time variability of the point sources. We also use the NWAY algorithm to search for multi-wavelength counterparts to these sources. Finally, we present updated results from a spectral analysis of the diffuse thermal emission.

Co-Authors: Katharina Egg, Manami Sasaki, Joern Wilms, Michael Nowak, Natalie Hell, Victoria Grinberg, Richard Rothschild (Remeis Obs./ECAP/FAU, Remeis Obs./ECAP/FAU, Remeis Obs./ECAP/FAU, Washington Univ. St. Louis, LLNL, IAA-Tuebingen, UCSD-CASS)

We re-investigate the available X-ray observations of the Cartwheel galaxy with the main aim of studying the X-ray variability pattern of the point sources. The Cartwheel is known to be the galaxy with the highest number of detected ULX - sources in excess of the Eddington luminosity for a stellar black hole. Indeed, albeit most of the ULXs are thought to be binary systems, we do not know yet what powers the majority of the system: a neutron star, as ascertained for at least five sources, or a black hole, which would be more in tune with the high luminosity observed? To this aim we have started a systematic search of the variability pattern of ULX in the Cartwheel, in order to estimate their frequency, span in luminosity and so on. The results will be linked also to the environment of the Cartwheel: a catastrophic impact that gave rise to a star formation burst in a low metallicity region. We are therefore analyzing the superb quality MUSE data in order to understand the timing of the burst and the metallicity in the region of Star Formation, where also the majority of ULXs is found.

Co-Authors: Marcella Longhetti, Chiara Salvaggio, Antonella Fruscione (INAF-Osservatorio di Brera, INAF-Osservatorio di Brera & Università degli Studi di Milano, SAO)

Recent studies suggest that the X-ray emission from high mass X-ray binaries (HMXBs) could be significant in pre-heating the intergalactic medium, prior to reionization, during the Epoch of Heating (EoH). While the early Universe is still inaccessible to Chandra and current X-ray telescopes, we have been studying the X-ray emission from nearby analogs of high-redshift galaxies to better constrain the X-ray emission from primordial galaxies. We have selected a sample of H-alpha emitters (HAEs), which have large Hα equivalent widths (EW(Hα)>500Å, suggestive of bursts of star formation within <6 Myr), SFR >1 M_⊙/yr and low metallicities (Z < 0.25Z_⊙), to study a clean sample of youngest, metal-poor galaxies, potentially containing the most luminous X-ray binaries, in the nearby (z<0.1) Universe. Galaxies with sub-solar metallicities appear to have higher L_X/SFR, due to weaker stellar winds which lead to more numerous and luminous HMXBs. However, the HAEs appear to have considerably lower X-ray luminosities given their high SFRs and low metallicities. The large range of EW(Hα) spanned by our study allows us to investigate the potential connection between extreme youth (young stellar age) and suppressed X-ray emission. We will present our results and their implications on predictions for heating by HMXBs in the early Universe.

Co-Authors: Mihoko Yukita, Panayiotis Tzanavaris, Bret Lehmer, Ann Hornschemeier, Tassos Fragos, Andreas Zezas (JHU/NASA GSFC, UMBC/NASA GSFC, U. Arkansas, NASA GSFC, Geneva Observatory, CfA/U. Crete)

Ultra-luminous X-ray sources or ULXs are sources with X-ray luminosities exceeding the Eddington limits of neutron stars and stellar-mass black holes (>10³⁹ erg s^-1). Observed X-ray variability suggests that they are X-ray binary systems. With the discovery of X-ray pulsations in some of these objects (e.g. M82 X-2), a certain ULX population is implied to have a neutron star as the accretor. We present a model to explain these pulsating ULXs as intermediate-mass X-ray binaries transferring mass at super-Eddington rates with effects on the observed accretion rate from beamed emission. Using MESA, we produce an allowed initial parameter space to form systems which could explain the observed luminosities of ULXs. The stability of these systems depends strongly on the response of the donor star to mass loss. We show that super-Eddington luminosities can be achieved with timescales of ∼10⁴-10⁶years undergoing non-conservative mass transfer, in a solar metallicity environment, provided the emission is beamed. We compute the orbital evolution of these intermediate-mass X-ray binary systems studying also the conditions that lead to merging scenarios or loss of tidal synchronization. Using two values for the initial neutron star mass (1.3 M_⊙ and 2.0 M_⊙) we present two sets of mass-transfer calculation grids, for comparing with observations of NS ULXs. We also compare our results to the observed pulsating ULXs and infer their initial parameters. Our results suggest that a large subset of the observed pulsating ULX population can be explained by IMXBs in a high mass-transfer rate phase.

Co-Authors: Tassos Fragos, Thomas Tauris, Emmanouil Zapartas, D. R. Aguilera-Dena, Pablo Marchant (University of Geneva, Aarhus Institute of Advanced Studies, University of Geneva, University of Bonn, Northwestern University)

The search for ultra-compact systems with periods<10 min is important not only to understand extreme phases of binary evolution, but also to constrain the kind of systems that might be detectable by LISA. We discover a previously unnoticed X-ray source with a periodic variability at 614.28s(probability of false alarm about 3.5e-4). Its X-ray spectrum is described by an absorbed 1.8keV blackbody plus an iron-line feature. It has a Lx about 1.2×10³⁴×(D/10 kpc)² erg s^-1 and has no obvious optical counterpart(fx/fo larger than 1600). Its faint radio counterpart shows evidence of having a positive spectral index (S_ν∝ν^α). We argue it is most likely a neutron-star ultra-compact X-ray binary with the shortest orbital period so far.

Co-Authors: Jane Kaczmarek, Roberto Soria, Frank Haberl (NAOC, CSIRO, MPE, Caltech)

With its unrivaled X-ray imaging capabilities, Chandra has opened our eyes to scales as smalls as just a few parsecs in nearby AGN. In order to "image"scales on micro-parsec scales in these nearby black holes, we currently rely on time domain techniques, and reverberation mapping in particular, that measures light echoes off the inner accretion disc near the innermost stable circular orbit. For stellar-mass black holes, reverberation has the same physical origin, but the black hole mass difference leads to much shorter time lags. The Neutron Star Interior Composition Explorer (NICER) has excellent sensitivity and an unprecedented time resolution, enabling us to perform simultaneous spectral modeling and timing analysis on the same observations. In this talk, I will present the current status of black hole transient studies with NICER, including results on GX 339-4 and MAXI J1820+070. The focus will be the evolution of physical quantities measured by spectral-timing modeling during outbursts, and I will discuss their implications for unanswered questions in black hole astrophysics, including state transition mechanism, the disk-corona geometry and coupling.

Co-Authors: Erin Kara, James Steiner, Javier Garc{\'\i}a, Jeroen Homan, Joseph Neilsen, Gr\’egoire Marcel, Renee Ludlam, Francesco Tombesi, Edward Cackett, Ron Remillard (MIT, CfA, Caltech, Eureka Scientific, Villanova University, Villanova University, University of Michigan, University of Maryland, Wayne State University, MIT)

We can learn a lot about the formation of compact objects, such as neutron stars and black holes, by studying the X-ray emission from accreting systems in nearby star-forming galaxies. The harder (E>10 keV) X-ray emission in particular allows strong discrimination among the accretion states and compact object types.A NuSTAR survey of M33 was conducted to study the distribution of X-ray binary (XRB) accretion states in an actively star-forming environment. The 6 NuSTAR observations of M33 allow us to construct diagnostic diagrams, which is used to infer XRB accretion states.

We have characterized XRB accretion states for ≈32 sources. The XRBs are classified by their compact object types using NuSTAR color-intensity and color-color diagrams. We further characterize the black holes by their accretion states (soft, intermediate, and hard) and the neutron stars by their weak or strong (accreting pulsar) magnetic field. In contrast to a similar NuSTAR survey of M31 (with a low-mass XRB-dominant population), the source population is dominated by high-mass XRBs, allowing the study of a very different population with similar sensitivity. These results provide a significant improvement in our knowledge of high-mass XRB accretion states that proves valuable for theoretical XRB population synthesis studies.

Co-Authors: Daniel R. Wik1 Ann Hornschemeier2, Bret Lehmer3, Paul Plucinsky4,Lacey West3, Thomas Maccarone5, Benjamin Williams6, Frank Haberl7, Andrew Ptak2, Mihoko Yukita2,8,Andreas Zezas4,9, Neven Vulic2,10, Vallia Antoniou4, Dominic Walton11, and Kristen Garofali3 (1Department of Physics and Astronomy, the University of Utah, Salt Lake City, Utah 84112, USA2 NASA Goddard Space Flight Center, Greenbelt, MD, United States. 3 University of Arkansas, Fayetteville, AR, United States. 4 Harvard-Smithsonian Center forAstrophysics, Cambridge, MA, United States. 5 Texas Tech University, Lubbock, TX, United States. 6 University of Washington, Seattle, WA, United States. 7 Max-Planck-Institut fur extraterrestrische Physik, Garching, Germany. 8 The Johns Hopkins University, Baltimore, MD, United States. 9 University of Crete, Heraklion, Crete, Greece. 10University of Maryland,College Park, MD, United States. 11 University of Cambridge, Cambridge, United Kingdom.)

We present the analysis of X-ray data for all galaxies within a radius of 200 Mpc observed with XMM-Newton. This sample is the result of cross-correlation between the XMM-Newton archive and the HECATE catalogue, the most complete galaxy catalogue (∼165,000 galaxies) of the local universe incorporating robust distances and stellar population parameters. In our analysis we use data from all objects observed by XMM-Newton, including those with no formal detections (i.e. upper limits). The sample contains 3000 galaxies observed in more than 2100 observations. Using the full set of archival XMM-Newton data, we measure their integrated X-ray luminosity in order to study the correlation between X-ray luminosity, star-formation rate, and stellar mass. Furthermore, we perform detailed spectral fitting for all galaxies with adequate number of counts (1715 galaxies), in order to measure their spectral parameters and to identify the AGN in our sample. Since the existing X-ray correlations on star-formation rate and stellar mass have been based on a few dozens of galaxies, this much larger sample provides the opportunity to cover the full range of star-formation rate and stellar mass in the local Universe. In addition, the large size of the sample enables us to characterize stochastic effects in these scaling relations.

Co-Authors: Frank Haberl, Andreas Zezas, Konstantinos Kovlakas (MPE, CfA, University of Crete/FORTH)

It is well known that X-ray luminosity (L_X) originating from high mass X-ray binaries (HMXBs) is tightly correlated with the host galaxy's star formation rate (SFR). We explore this connection using a sample spanning ∼4 dex in SFR and ∼3 dex in specific SFR (sSFR) along with a comprehensive set of star-formation (24μm, 8μm, Hα), stellar mass (3.6μm) indicators, and Chandra observations. We investigate the L_X-SFR and L_X-stellar mass (M_⋆) scaling relations down to sub-galactic scales of 1 kpc². This way we examine these correlations to extremely low SFR (∼10^-6 M_⊙ yr^-1) and M_⋆ (∼10⁴ M_⊙). We find good agreement with established relations down to SFR∼10^-3 M_⊙ yr^-1 and an excess of L_X for lower values. We finally show evidence that the excessive L_X arises from low mass X-ray binaries (LMXBs). We also find that the intrinsic scatter of the L_X-SFR relation is not correlated with SFR. Finally we find variations between the scaling relations for different SFR indicators, with Hα showing the tightest correlation. We attribute this to the fact that Hα probes stellar population ages similar to those of HMXB formation timescales.

Co-Authors: Andreas Zezas, Paul Sell, Konstantinos Kovlakas, Paolo Bonfini, Mathew Ashby, Steven Willner (IA-FORTH/U. of Crete/CfA, IA-FORTH/U. of Crete, IA-FORTH/U. of Crete, IA-FORTH/U. of Crete, CfA, CfA)

Ultraluminous X-ray Sources (ULXs) are X-ray binaries with luminosity above the Eddington limit for an accreting stellar mass black hole. Their high mass accretion rates challenges our understanding of accretion physics. Probing their nature and evolution can provide valuable input to the study of single/binary stellar evolution, as well as gravitational wave sources (ULXs as progenitors of NS/BH mergers.)

By cross-matching the Chandra Source Catalog 2.0 with HECATE, a newly compiled galaxy catalog of the local Universe (<200 Mpc), we construct the largest census of ULXs in the local Universe. We study the connection of ULX populations with the properties of their host galaxies such as morphology, star formation rate, stellar mass and metallicity.

We estimate the number of ULXs as function of SFR (in late-type galaxies) and stellar mass (in early-type galaxies) confirming previous results, as well as for different morphological types. Furthermore, we extend the scaling relation to account for both SFR and stellar mass of the host galaxies. We find 0.55 ULXs per SFR and 3.5 ULXs per 10¹² stellar mass, in agreement with the expectation from Low- and High-mass X-ray binary luminosity functions. In addition we find evidence for an excess of ULXs in low metallicity and low mass galaxies with respect to the average in late-type galaxies, lending support to the association of ULXs with young stellar populations and low-metallicity environments. In addition, we find a lack of ULXs in lenticular galaxies with respect to elliptical galaxies.

Luminous infrared galaxies (LIRGs), the most extreme star-forming galaxies in the nearby Universe, show a notable X-ray emission deficiency as compared with predictions from well-characterized scalings of the high mass X-ray binary (HMXB) luminosity function with star-formation rate. In the nearby LIRG NGC 7552, the majority of the IR emission originates in a circum-nuclear starburst ring, which has been resolved into several discrete knots of star formation. In this poster, we present results from recent Chandra observations of NGC 7552, which reveal a major deficit in the 2-7 keV X-ray emission from two of the three most powerful star-forming knots. The luminous HMXB populations in these knots are thought to be either (1) missing due to relatively high metallicity and/or young ages in these knots or (2) obscured by a very large column density. We aim to distinguish between these possibilities with data from upcoming NuSTAR observations, whose sensitivity above 10 keV is expected to uncover any obscured HMXB population since emission at these energies is more immune to absorption effects.

Co-Authors: Lacey West, Bret Lehmer, Andrea Prestwich, Rafael Eufrasio, Kristen Garofali, Wasutep Luangtip, Tim Roberts, Andreas Zezas (University of Arkansas, University of Arkansas, Harvard-Smithsonian Center for Astrophysics, University of Arkansas, University of Arkansas, Srinakharinwirot University, Durham University, Harvard-Smithsonian Center for Astrophysics)

We present a comprehensive study of the northern disk of M31 using the strengths of three missions: the multi-band optical photometry from the Hubble Space Telescope (Panchromatic Hubble Andromeda Treasury, PHAT) to distinguish sources in M31 from foreground and background sources, the precise position from Chandra to associate the X-ray source with the optical source, and the X-ray spectral information from XMM-Newton. After sources were identified based on the analysis of Hubble and Chandra data, we determined the spectral properties of all detected XMM-Newton sources by using hardness ratios and, if the statistics were sufficient, by extracting the spectrum from each source. We also checked for variability. We identified 43 foreground stars and candidates and 50 background sources. Based on a comparison with the results of the Chandra/PHAT survey, we classify 24 hard X-ray sources as new candidates for X-ray binaries. In total, we identified 34 X-ray binaries and candidates and 18 supernova remnants and candidates and compiled a complete list of X-ray sources down to a sensitivity limit of ∼7×10³⁴ erg s^-1 (0.5-2.0 keV). We also used all existing XMM-Newton data to create a mosaic which gives the most detailed view of the hot interstellar medium (ISM) in a grand design spiral galaxy such as our own. We performed a spectral analysis of the extended X-ray emission. Based on the deep XMM-Newton observations of the northern disk of M31 we show that the massive stars in the northern disk and, in particular, in the 10 kpc star-forming dust ring are responsible for heating the ISM to X-ray emitting temperatures.

Co-Authors: Patrick J. Kavanagh, Frank Haberl, Martin Henze, Sara Saeedi, Benjamin F. Williams, Paul P. Plucinsky, Despina Hatzidimitriou, Kirill V. Sokolovsky, Dieter Breitschwerdt, Miguel A. de Avillez, Miroslav D. Filipovic, Timothy Galvin, Margaret Lazzarini, Knox S. Long (0.0)

The ChandraPHAT survey is a 350 ks Chandra Large Project consisting of seven 50 ks exposures in the star forming disk of Andromeda (M31). ChandraPHAT was designed to overlap with the survey area of the Panchromatic Hubble Andromeda Treasury (PHAT), a UV/optical/IR survey covering one third of the star forming disk of M31, resulting in six band photometry for over 100 million individual stars. Hard X-ray observations with NuSTAR also overlap the ChandraPHAT survey area in M31. Using Chandra source positions to link high mass X-ray binaries (HMXBs) detected by HST and NuSTAR allows us to study HMXBs in M31 from the near IR to hard X-rays, providing observational constraints on both the compact accretor and companion star in these systems, with Chandra providing the absolutely critical link to go between high spatial resolution HST data and lower angular resolution data from NuSTAR.

We have a sample of about 40 HMXB candidates for which we have obtained age estimates, companion star UV/optical/IR magnitudes from HST, and X-ray luminosities with Chandra. We were able to identify candidate companion stars and determine their spectral types and ages. We determine likely ages using spatially resolved recent star formation histories from the PHAT survey and determine spectral types with SED fitting using the Bayesian Extinction and Stellar Tool (BEAST). We pair Chandra and NuSTAR measurements to compare hard X-ray colors and luminosities of a subset of our HMXB candidates with Galactic HMXBs of known accretor type, which allows us to distinguish between black hole and neutron star accretors.Taking our HMXB candidates as a sample, we compare their characteristics with models from the new state of the art binary population synthesis (BPS) code, PSyLib. We use spatially resolved star formation histories as inputs into PSyLib and then compare the model HMXB population (X-ray luminosities, magnitudes in the HST bands, and ages) with our observed population to place constraints on parameters describing the late stages of massive stellar binary evolution.

Co-Authors: Benjamin F. Williams, Ann Hornschemeier (University of Washington, Goddard Space Flight Center code 662)

Ultraluminous X-ray sources (ULXs) are a class of objects with characteristically large luminosities above a threshold of ∼10³⁹ erg/s, exceeding the Eddington luminosity. There are over 400 ULX candidates (Walton et al. 2011), and most of them are thought to be in black hole X-ray binaries. However, in 2014, the first ULX with significantly detected pulsations was discovered. NGC 300 ULX-1 is one of the six known ULX pulsars, with a luminosity of ∼5×10³⁹ erg/s (Carpano et al. 2018) from NuSTAR and XMM-Newton observations. Its spin period has exponentially evolved from ∼126 s to ∼18 s over a period of 4 years, yielding an average frequency derivative of 3.8×10^-10 Hz/s. Chandra, NuSTAR, and Swift conducted follow-up observations in 2017 and 2018 which showed that these pulsations and super-Eddington luminosities persisted. To complement previous analyses, we analyzed over 200ks of NICER observations spanning over most of 2018 into early 2019, as well as XMM-Newton data, looking for line features. We will present the evolution in the hardness-intensity diagram, and show how spectral parameters have changed as a function of luminosity.

X-ray binaries (XRBs) are signposts for the remnants of massive stars and thus provide important constraints on massive stellar evolution. Additionally, XRBs are key to understanding the progenitor paths for gravitational wave sources. Star-forming galaxies are ideal environments in which to find particularly rare systems, such as potential gravitational wave progenitor Wolf-Rayet XRBs. We present results from a recent 160 ks continuous Chandra observation of the candidate Wolf-Rayet XRB in the nearby starburst galaxy NGC 253. The previously reported 15 hr orbital period could not be confirmed, possibly due to outflows from the binary system. Using Hubble Space Telescope photometry we constrain the companion stellar type. Incorporating archival Chandra and NuSTAR observations, we summarize the properties of variable sources and study the 1-30 keV X-ray luminosity function. We compare the observed X-ray luminosity function to results from population synthesis modeling based on the star formation history of NGC 253.

Co-Authors: N. Vulic, A. E. Hornschemeier, M. Yukita, B. D. Lehmer, T. J. Maccarone, A. Zezas (University of Maryland College Park/NASA GSFC, NASA GSFC/John Hopkins University, John Hopkins University/NASA GSFC, University of Arkansas, Texas Tech University, University of Crete)

We provide an analysis of extragalactic X-Ray sources in seven edge-on spiral galaxies with the goal of locating Ultra Luminous X-Ray (ULX) source candidates. We target edge-on spirals so that we can disentangle and compare the population of Low Mass X-Ray Binaries (LMXB) with High Mass X-Ray Binaries (HMXB). With data from the Chandra Data Archive, we fit each source to disk black body and power law models using XSPEC in order to identify differences between the two populations. We also determine which sources are contaminating background galaxies as opposed to ULX candidates within our spiral galaxies of interest. Hence we provide a catalogue of both high and low mass X-Ray binary ULX candidates in these seven galaxies and the surrounding areas. We then construct histograms to compare the distributions of internal disk temperatures and power law indices for our LMXBs and HMXBs. However, we are unable to conclude that LMXBs are significantly different from HMXBs in terms of internal disk temperature or power law index. Additionally, we present the discovery of a new extreme ULX with L_x > 10⁴⁰ erg/s.

Co-Authors: Kristen Dage, Arunav Kundu, Erica Thygesen, Jay Strader (Michigan State University, Eureka Scientific, Michigan State University, Michigan State University)

We present the results of 150 ks of new Chandra-ACIS observations and roughly a mega-second of Swift-XRT observations of the high-mass TeV binary HESS J0632+057. The Chandra data were taken at the X-ray lightcurve minimum to look for compact extended emission similar to that resolved around the famous TeV binary PSR B1259−63/LS 2883. The analysis of the Chandra data have shown hints of extended emission up to 5'' SE of the binary. On arc-minute scales we have found an extended (about 1' in diameter) emission clump located about 5' east of the binary. The extended clump does not appear to have a counterpart at lower wavelengths, while its spectrum can be described by the a power-law with a photon index of 2.5. The clump is also clearly seen in the combined XRT image. We have also fitted the Chandra and XRT spectra of the binary itself and explored the variations of spectral parameters with orbital phase taking advantage of the excellent Swift-XRT coverage. We find that the flux from the binary can vary by a factor of 2 on time scales as short as days even at the lightcurve minimum, while the spectral index remains unchanged. We discuss the implications of our results for the emission mechanism and the nature of the compact object. We also explore the perspectives for future observations.

Co-Authors: Noel Klingler, Oleg Kargaltsev, George Pavlov, Jeremy Hare (The Pennsylvania State University, The George Washington University, The Pennsylvania State University, University of California Berkeley)

Ultracompact X-ray binaries (UCXBs) are binaries with a neutron star accretor and an orbital period less than 80 minutes. Here, I focus on our comprehensive review of Chandra observations of the unique UCXB 4U 1626-67, the only known UCXB to host a strongly-magnetized accreting pulsar. Our sophisticated modeling of the X-ray gratings spectra finds intriguing results: we observe strong, double-peaked emission lines of neon and oxygen, consistent with an accretion disk made up of a collisionally-ionized, two-temperature, pure Ne/O plasma. This is in tension with several expectations: the X-ray pulsar was expected to produce a photoionized plasma, not collisional; the temperature structure is difficult to produce within the small range of orbital distances implied; and the composition of the donor is out of line with any standard white dwarf model. However, we believe we have come up with a coherent picture of this source that reconciles most of these conflicts, which I will present.

Co-Authors: Norbert Schulz, Deepto Chakrabarty, Herman Marshall (MIT, MIT, MIT)

In the absence of a bright active galactic nucleus, X-ray binaries (XRBs) – systems in which a compact object accretes mass from a companion star – dominate the high energy emission of a star-forming galaxy. Collectively, the properties of these systems show correlations with the properties of the host galaxy: the total luminosity and number of binaries with low mass donor stars (M ≤ 3 M_sun) scale with total stellar mass in elliptical galaxies, while the X-ray luminosity function (XLF) of binaries with high mass donor stars (M ≥ 8 M_sun) scales with star formation rate in spiral galaxies. Because separating XRBs by mass cannot be done directly using X-ray properties alone, previous studies have been unable to fully account for contamination from low-mass XRBs in the XLF of high-mass XRBs in late-type galaxies. Furthermore, evidence suggests the XLF for low-mass XRBs in late-type galaxies is not the same as for early-type galaxies. To address these issues, I combine archival Chandra deep imaging with multi-band, high-resolution photometry from the Hubble Space Telescope in order to directly constrain the masses of XRBs within the nearby spiral galaxy M83. In doing so, I will create uncontaminated XLFs for both high- and low-mass XRBs in a star-forming galaxy, which may ultimately allow us to use the XRB scaling relations on similar star-forming galaxies at larger redshifts.

Co-Authors: Elena Gallo, Rupali Chandar, Paula Johns Mulia, Angus Mok, Andrea Prestwich (University of Michigan, University of Toledo, University of Toledo, University of Toledo, Harvard-Smithsonian Center for Astrophysics)

Ultra-luminous-X-ray (ULX) sources have been identified with both pulsars and black holes. We have extracted lightcurves of over a 100 ULXs from the Chandra Source Catalog 2.0. We have also extracted lightcurves of extragalactic X-ray binary candidates from 100 external galaxies and of X-ray binaries in our own Galaxy using the same energy bands as provided in the catalog (0.5-7.0keV; 0.5-1.2keV; 1.2-2.0keV; 2.0-7.0keV). Luminosities of extragalactic objects were calculated using distances as given by NED; luminosities of the Galactic sources calculated using distance from parallaxes obtained with GAIA. We find that the point sources associated with external galaxies extend to much higher luminosities (up to two orders of magnitude) than XRBs within our Galaxy and the Magellanic Clouds. We depict XRBs from our own Galaxy and external galaxies together with ULXs in a single color-color-luminosity plot . We find we can determine the population of ULXs that align with the low/hard state of black hole XRBs versus those that align with systems containing pulsars.

Co-Authors: S. D. Vrtilek, D.-W. Kim, B.Boroson, M. McCollough , N. Islam, and the Chandra Galaxy Atlas Team (Center for Astrophysics | Harvard & Smithsonian)

The Galactic X-ray binary SS 433 is the only known astrophysical object to exhibit strong, relativistically red- and blue-shifted lines from elements such as S, Si, Fe, Ni. The X-ray emission lines originate in a jet outflow that is launched somewhere very close to the compact accretor (a black hole or a neutron star). During 2018 August 10-14, SS 433 was observed using the High Energy Transmission Grating Spectrometer system on Chandra. During this epoch, one 20 ksec observation was made three days before an eclipse of the compact object by the donor, and then a 96 ksec observation was made starting shortly after mid-eclipse (orbital phase of 0.109). The observations were designed to take advantage of the eclipse and carry out time-resolved spectroscopy to infer spatial variation of physical properties such as composition, temperature, and density at different distances along the jet. In addition to phenomenological fits to determine the properties of the observed emission lines, we will present results from fitting collisionally ionized plasma models. While the observed Doppler shifts of the emission lines in the Western jet are close to their ephemeris predicted values, the Doppler shifts of the lines from the Eastern jet differ significantly from predictions (observed redshift = 0.0345 ± 0.0005; predicted range: 0.078 - 0.096). We are currently trying to understand the origin of this 'unruly' behavior of SS 433's jets, which has sometimes been noticed in previous observations of SS 433 as well.

Co-Authors: Xinyi Liu, Herman Marshall, Dipankar Maitra, Mike Nowak, Norbert Shulz, Diego Altamirano, Jack Steiner (Wheaton College, MA, MIT Kavli Institute, MA, Wheaton College, MA, Washington University at St. Louis, MO, MIT Kavli Institute, MA, University of Southampton, England, MIT Kavli Institute, MA)

The discovery of a magnetar (PSR J1745-2900) at parsecs distance from the Milky Way central black hole, Sagittarius A⋆, represents the closest pulsar to a black hole ever detected. Furthermore, its intriguing radio emission has been used to study the environment of the supermassive black hole, as well as deriving a precise position and proper motion for this strongly magnetized neutron star. This discovery opened interesting debates about the number, age and nature of pulsars expected in the Galactic center region. In this work we present X-ray monitoring of this magnetar outburst using the Chandra X-ray Observatory, the only instrument having the spatial capabilities to resolve the magnetar from the central supermassive black-hole (at only 2.4''angular distance). PSR J1745-2900 was monitored from its outburst onset in April 2013, until July 2019, collecting more than 54 Chandra observations for a total of more than 2.3 Ms of data. The outburst evolution of this magnetar is the best studied to date, and allowed stringent constraints on the physics of the neutron star surface involved in such a slow outburst cooling.

Co-Authors: Frederick Baganoff, Nanda Rea, Francesco Coti Zelati, Daryl Haggard, Gabriele Ponti, on behalf of a larger collaboration (MIT, IEEC-CSIC, IEEC-CSIC, McGill University, INAF-Osservatorio Astronomico di Brera)

Long period pulsars (P>1000 s) constitute a sub-population of high-mass X-ray binaries (HMXB), and occupy the tail of the spin period distribution of X-ray pulsars,To date, only a few of these rare systems have been discovered. We report on the discovery of candidate and confirmed long period pulsars located in the Large Magellanic Cloud (LMC), based on XMM-Newton observations. These systems have persistent X-ray luminosities and seem to accrete from supergiant (Sg) companions. Their discovery confirms the presence of higher percentage of HMXBs with Sg donor in the LMC compared to the Small Magellanic Cloud. Thus, their study offers unique insights into evolutionary scenarios of the high-mass X-ray binary population.

Co-Authors: Frank Haberl, Maria Petropoulou, Chandreeye Maitra (MPE, Princeton, MPE)

There have been many observations of weak magnetic field neutron stars using the Chandra high and low transmission grating spectrometers (HETGS and LETGS). These include isolated neutron stars, weak field pulsars, type I X-ray bursts from neutron stars in X-ray binaries, and both type I and type II X-ray bursts from the Rapid Burster. The primary objective is to observe surface emission absorption features that can be identified in order to determine the gravitational redshift at the surface of the star, thereby measuring the ratio M/R, where M is the star's mass and R is its radius. The M/R ratio can be used with other estimates of M and R to determine the validity of M(R) models that depend on the equation of state of nuclear matter. A secondary objective is for accurate modeling of the neutron star atmosphere, which provides an estimate of R. No such features have yet been found, possibly due to gravitational settling of heavy metals and rotational broadening in the case of many neutron stars in binaries. This presentation will provide a summary of 20 years of observational results, including searches for absorption edges and lines characteristic of winds during atmospheric radius expansion.

Synchrotron X-ray images of pulsar wind nebulae (PWNe) map the shock structure of the relativistic e+/e-/B outflows of energetic pulsars. The PSR J1709-4429 PWN is a particularly interesting example, showing a distinct equatorial torus and narrow polar jets, which are swept back on 2' scales by the pulsar motion. The pulsar space velocity is unusually small so that its motion is transsonic. This means that the central torus/jets are not crushed by the bowshock, as is the case in several supersonic CXO PWNe (see Kargaltsev et al., this meeting). Thus the Doppler-boosted inner structures provide detailed knowledge of the 3-D orientation of the pulsar spin axis and jets so that the larger scale flow probes the physics of the jet confinement, energization and sweep-back. We report here on initial studies of a new sequence of four deep CXO images that provide a dramatic time-averaged view of the PWN morphology, while giving a glimpse of fine structure variations on the ∼10⁷s inter-epoch time scale. The epoch images show distinct changes in the 10 arcsec torus shocks while blob motion in the jets suggest beta_⊥∼0.05 in the inner counter-jet, and beta_⊥∼0.1 for the jet at arcmin scales. Comparison with archival images registered via X-ray field sources will better constrain the pulsar proper motion on the decade timescale. Finally on the largest scales, the relativistic particles energize the parent SNR G343.1-2.3 and the associated TeV source HESS J1708-443.

Co-Authors: Martijn de Vries, Roger Romani, Oleg Kargaltsev, George Pavlov, Bettina Posselt, Patrick Slane (KIPAC, George Washington University, Pennsylvania State University, Center for Astrophysics)

Pulsar wind nebulae (PWNe) are sources of nonthermal X-ray emission and prominent sites of particle acceleration. PSR J1809-1917 is a young and energetic radio pulsar powering a dynamic compact X-ray PWN. The nearby and much larger extended TeV source HESS J1809-193 is considered to be a relic PWN of PSR J1809-1917. We report the results of Chandra monitoring campaign which consists of six epochs spaced with 7-week intervals. The compact nebula displays interesting dynamics, changing in morphology and brightness across timescales of months. We detect a bright clump of X-ray-emitting plasma, comparable in luminosity to the pulsar itself, moving on the same timescales — likely the Doppler-boosted portion of a jet changing its orientation. The dynamics of the clump is more complex than just steady motion and could be reminiscent of the variability observed in the Vela pulsar jet. The deep exposure obtained by combining archival and new data (540 ks) reveals an arcminute-scale bow-shaped structure aligned with the compact nebula's axis of symmetry and pointed away from the HESS J1809-193 center. We also detect an elongated asymmetric structure which could be another instance of a misaligned outflow (a stream of high-energy particles leaking from the bow shock). We discuss the implications of our findings in the context of the broader sample of supersonic and relic PWNe.

Co-Authors: Noel Klingler, Oleg Kargaltsev, George Pavlov, Bettina Posselt (The Pennsylvania State University, The George Washington University, The Pennsylvania State University, Oxford University)

CXO observations have revolutionized studies of pulsar wind nebulae (PWNe). In particular, they have led to the discovery of X-ray emission from pulsar tails. These extended structures are ram-pressure confined regions behind supersonically moving pulsars filled with ultra-relativistic pulsar wind. CXO data on pulsar tails fueled theoretical and computational studies which include (but not limited to) mass entrainment, turbulence, reconnection, kinetic particle escape, and MHD modeling. We present the results from recent (and ongoing) observing campaigns where several supersonic PWNe (SPWNe) have been observed with deep CXO exposures. Using ACIS to perform spatially resolved spectroscopy, we found that some tails exhibit strong spectral softening along their lengths (consistent with rapid cooling) while others do not. The absence of cooling may require particle re-acceleration (e.g., via magnetic turbulence and reconnection). The unprecedented angular resolution of CXO also revealed distorted structures of compact nebulae associated with long pulsar tails, which allows one to study the connection between the properties of both compact and extended components and with the gamma-ray and radio light curves of the pulsars. Finally, deep ACIS images of several SPWNe revealed completely unexpected structures dubbed "misaligned outflows" (a.k.a. kinetic jets) that can extend for several parsecs at large angles with respect to the pulsar velocity, have hard spectra, and exhibit puzzling morphologies.

Co-Authors: George Pavlov, Noel Klingler, Bettina Posselt, Roger Romani, Patrick Slane (Pennsylvania State University, Pennsylvania State University, Pennsylvania State University, Stanford University, Harvard University)

Polestar is a vector-based model we’ve designed to determine the gross geometrical characteristics and orientation of X-ray pulsars (XRPs) through a computationally inexpensive Python code. In conjunction with our collected database of all Chandra observations of the SMC spanning from first light to the present, Polestar has fit over 50 unique pulse profiles from the XRP SXP348. In addition to a determination of the most-likely configuration for this system, an event associated with a period of no significant pulsations followed by a change in emission geometry was discovered. We are currently fitting profiles from other XRPs in the SMC, with future plans of fitting profiles from all known XRPs, both galactic and extra-galactic, with Polestar.

Co-Authors: Silas G. T. Laycock, Dimitris M. Christodoulou, Ankur Roy, Sayantan Bhttacharya (University of Massachusetts Lowell (UML), UML, UML, UML)

For the spectral analysis of hot, compact stars, advanced model atmospheres that consider deviations from the local thermodynamic equilibrium (LTE), are mandatory. The Tübingen Non-LTE (NLTE) Model-Atmosphere Package (TMAP) can calculate such model atmospheres and spectra at a high level of sophistication. These NLTE spectra can be used, e.g., for the analysis of accreting white dwarfs in cataclysmic variables.

We present existing grids of synthetic spectral energy distributions and their application to novae and supersoft X-ray sources.

X-ray Isolated Neutron Stars (XINSs) are thermally emitting neutron stars. Their spectra have been reproduced with a single-temperature blackbody (1BB) model with the temperature of kT∼40-100 eV. From their pulsation, the age and magnetic field is estimated to be τ∼1 Myr and B∼10¹³ G. On the basis of spectral and timing parametres, it have been often speculated that XINS are aged, cooled magnetars ("worn-out"hypothesis). Here we report that all 7 XINSs show a high-energy component in addition to the 1BB model, namely "keV-excess". Analyzing all the XMM-Newton data for the XINSs with the highest statistics ever achieved, we find that their X-ray spectra are all reproduced with a dual-temperature BB (2BB) model, similar to magnetars. The spectral parametres are also similar to those of magnetars. The remarkable similarity in the spectra between XINSs and magnetars suggests that the origins of their emissions are the same.

Co-Authors: Kiyoshi Hayashida, Hiroshi Nakajima, Hironori Matsumoto (Osaka University, Kanto-Gakuin University, Osaka University)

The isolated neutron star RX J1856.5-3754 has turned out to be a verystable X-ray source with a spectrum that is best described using a black-body function. Unlike other isolated neutron stars this object has remained stable over the life time of the Chandra X-ray observatory. With a black-body temperature of about 700 kK it turns out to be an ideal object to use as a calibration source for X-ray observatories that are sensitive in the 0.1-1.0 keV range. In the context of calibrating the low energy response of eROSITA new Chandra LETGS spectra of RX J1856.5-3754 were obtained in July this year. These spectra will be presented here.

Co-Authors: Frank Haberl, Konrad Dennerl (0.0)

Violent (>100x amplitude), short-term (<1 minute rise time) X-ray flaring from a host of astrophysical objects have been increasingly detected in recent years from Milky Way stars, extragalactic X-ray binaries in nearby galaxies, and other transients at cosmological distances of uncertain origin. Our thorough search of the Chandra data archive for flaring objects has uncovered a number of such flares that have escaped notice until now. We present a summary of the most extreme X-ray flaring events from both our survey and the literature and discuss how such violent events further our understanding of stellar magnetic fields, compact object accretion, and compact object mergers.

X-ray binaries, composed of a compact object (neutron star or black hole) orbiting around a companion star, constitute an excellent environment to study accretion phenomena, one of the most promising challenges in modern astrophysics. Outstanding open topics include the interplay between outflows (in the form of collimated winds or relativistic jets) and discs, the accretion-radiation energy balance, the radiative feedback and the relation between relativistic jets and the fundamental properties of the black holes (e.g. spin). Here, we report the analysis of two black hole low mass X-ray binaries, 4U 1630-47 and IGR J17091-3624, using X-ray high-resolution spectra. In the case of 4U 1630-47, we found that the absence of lines in the transitional state cannot be attributed to an evolution of the plasma caused by thermal instabilities. Instead, the disappearance of the wind could indicate an acceleration of the flow or that the plasma has been exhausted during the soft state. For IGR J17091-3624 we have identified an intrinsic ionized static absorber during a transition from a hard accretion state to a hard-intermediate accretion state. Such an absorber could be a permanent structure or a previous state of an outflowing wind.

Co-Authors: M. Díaz-Trigo, J. C. A. Miller-Jones, S. Migliari (European Southern Observatory (ESO), International Centre for Radio Astronomy Research, XMM-Newton Science Operations Centre)

SgrA*, at the heart of our galaxy, presents a unique opportunity to understand a supermassive black hole system at close distance. Recently, Chandra X-ray observations have detected bright flares from SgrA* with in-depth spectral analysis showing the short timescale variability. I will discuss the timing analysis of X-ray flares produced by high-resolution simulations using our state of the art GPU general relativistic magneto-hydrodynamics code H-AMR. GRAVITY NIR observations indicate orbital motions of a flaring event, which might be a hotspot traveling along with the accretion flow or possibly an outflow. The amount of magnetic flux contained in the disk changes the nature of the accretion flow, potentially giving rise to small plasmoids of magnetic flux that might be the source of flaring episodes and non-thermal activity. Furthermore, I will touch upon simulations featuring disks misaligned to the black hole spin axis, where the tilted geometry promises more complicated flows that can lead to X-ray flares. Such studies may provide new insights in decoding the mechanism behind flaring in SgrA* and interpreting future Event Horizon Telescope results for the near-horizon image of SgrA*.

Co-Authors: Sera Markoff, Alexander Tchekhovskoy, Matthew Liska, Ziri Younsi (University of Amsterdam, Northwestern University, Harvard University, University College London)

Over the previous two decades, general relativistic magneto-hydrodynamic (GRMHD) simulations have contributed immensely towards understanding the evolution of low-luminosity black hole accretion disks and relativistic jet launching, with increasing computational resources in recent years enabling highly resolved disk turbulence. Using our group’s state of the art GPU-accelerated GRMHD code H-AMR, we have performed black hole accretion simulations both with and without self-consistent radiative cooling, scaled to the mass and distance of Sagittarius A*, the supermassive black hole at the heart of our galaxy. In the past 20 years, continuous Chandra monitoring of SgrA* has resulted in a vast reservoir of flare statistics that allowed in-depth spectral analysis. In addition, recent GRAVITY NIR observations indicate orbital motions of a hotspot linked to a flaring event. Such hotspots might occur as a result of non-thermal activity from small plasmoids of magnetic flux, which travel along with the accretion flow or possibly an outflow. I will discuss the challenges in producing X-ray flaring from non-thermal synchrotron emission from such plasmoid structures in simulations. Furthermore, I will touch upon simulations featuring disks misaligned to the black hole spin axis, where the tilted geometry promises more complicated flows. These studies may provide new insights for accretion disks, relevant for better understanding Chandra’s observations of black holes. Such simulations will be important for interpreting the upcoming Event Horizon Telescope results for the near-horizon image of SgrA*.

Co-Authors: Sera Markoff, Ziri Younsi, Matthew Liska, Alexander Tchekhovskoy (University of Amsterdam, University College London, Harvard University, Northwestern University)

Ultra-fast Outflows in AGN were first suggested based upon low spectral resolution CCD data in the 6-8 keV range, and were ascribed to absorption by highly ionized Fe. In this region, CCD resolution isn't dramatically below that of gratings. Further evidence for UFOs has been claimed from high spectral resolution observations with the XMM-Reflection Gratings Spectrometer, and has been extended to Ultra-Luminous X-ray sources. The <2 keV region, however, is extremely crowded, and UFO models often posit multiple absorbers with a range of blueshifts. It is not clear that even RGS resolution suffices. I discuss two recent UFO studies using the Chandra-HETGS. We gain from improved resolution, but suffer from low effective area. First, for the AGN PG1211+143, we were able to verify the presence of an absorber outflowing at 0.06 c. Next, for the ULX NGC 1313 X-1 we are still trying to determine if there is evidence for a UFO, and if not, do our observations contradict prior RGS studies?

Co-Authors: Michael Nowak, Claude Canizares, Alex Eaton, Ciro Pinto (WUSTL, MIT-Kavli, WUSTL, ESA/ESTEC)

The mechanisms that drive disk winds are a window into the physical processes that underlie the disk. Stellar-mass black holes are an ideal setting in which to explore these mechanisms, in part because their outbursts span a broad range in mass accretion rate. We performed a spectral analysis of the disk wind found in six Chandra/HETG observations of the black hole candidate 4U 1630-472, covering a range of luminosities over two distinct spectral states. We modeled both wind absorption and extended wind re-emission components using PION, a self-consistent photoionized absorption model. Two photoionized absorbers were required in order to obtain acceptable fits. Two independent constraints on launching radii, obtained via the ionization parameter and the dynamical broadening of the re-emission, helped characterize the geometry of the wind. The innermost wind components (r ≈ 10^2-3 GM/c²) tend toward high ionizations, densities up to n ≈10^15-16 cm^-3, and outflow velocities of ∼0.003c. These small launching radii, large velocities, and large densities require magnetic driving, as they are inconsistent with numerical and analytical treatments of thermally driven winds. Outer wind components (r≈10⁵ GM/c²) are significantly less ionized. Their larger launching radii, lower densities (n≈10¹² cm^-3), and outflow velocities (∼ 200 km/s) are nominally consistent with thermally driven winds. The overall wind density structure, however, suggests that these components may also be part of a broader MHD outflow. Once the observed outflow velocities are corrected for the gravitational redshift at their launching radius, the resulting wind velocity structure is also broadly consistent with a self-similar MHD wind.

Co-Authors: Nicolas Trueba, Jon Miller, Jelle Kaastra, Abderahmen Zoghbi, Andrew Fabian, Tim Kallman, Daniel Proga, John Raymond (University of Michigan, University of Michigan, Netherlands Institute for Space Research, University of Michigan, NASA Goddard Space Flight Center, University of Nevada Las Vegas, Harvard-Smithsonian Center for Astrophysics)

By enabling X-ray spectroscopy of AGN, the Chandra X-ray Observatory made it possible to test longstanding hypotheses regarding the origin and dynamics of multiphase gas on parsec and sub-parsec scales. Perhaps the most enduring idea is that relatively cool condensations ('clouds') can appear within highly ionized plasma via thermal instability (TI), thereby explaining intrinsic X-ray absorption and possibly broad line emission. Over the last several years, we developed a quantitative and detailed physical model revealing how cloud acceleration and destruction accompanies cloud formation through TI. Our model takes into account several important processes that determine the key properties of multiphase gas dynamics in the X-ray band. By self-consistently including radiation heating and cooling, thermal conduction, and radiation forces, our radiation-hydrodynamical (rad-HD) time-dependent simulations allow us to address fundamental issues such as the expected cloud mass and size distributions, cloud interactions, and the spectral signatures of such an accelerated, clumpy medium. In this talk, we will summarize the main results from our rad-HD simulations and from calculations of synthetic X-ray lines.

Co-Authors: Tim Waters (Los Alamos National Laboratory)

Black hole accretion and ejection are intimately correlated, making the disk-wind dynamic system a fundamental building block in the AGN/galaxy life-cycle. A major advance in this field has been obtained in the past 20 years thanks to Chandra and XMM-Newton high sensitivity X-ray spectroscopy, which allowed the discovery of a key ingredient in these systems: powerful semi-relativistic winds emerging from the innermost regions of the accretion disk. I will review both observations and models of semi-relativistic winds, showing that their interaction with the accreting matter may lead to a self-regulation of the accreting flow, and thus of the black hole growth and black hole feedback on its host galaxy.

High-resolution Chandra spectroscopy of the warm absorber in the nearby X-ray bright Seyfert 1 galaxy Mrk 1040 is presented. The superb spectral resolution of Chandra HETG allows us to resolve a multitude of absorption lines from Ne, Mg, and S, originating from a wide variety of ionization states. In particular, the detection of inner K-shell absorption lines, from charge states ranging from F-like to Li-like ions, suggests the presence of a substantial amount of low-ionization absorbing gas, illuminated by a steep soft X-ray continuum. The line profiles imply that the outflow velocities of the absorbing gas are low and within 100 km/s of the systemic velocity of Mrk 1040. This suggests that any outflowing gas has stalled in this AGN on large enough scales and is not sufficient to cause large scale galaxy feedback. The warm absorber is likely located far from the black hole, within 300 pc of the nucleus, and is spatially coincident with emission from an extended O III narrow-line region as seen in the Hubble Space Telescope images. The iron K emission line is consistent with originating from reflection off a Compton-thick pc scale torus.

Co-Authors: Valentina Braito, Ehud Behar, Travis Fischer, Steve Kraemer, Andrew Lobban, Emanuele Nardini, Jane Turner, Delphine Porquet (UMBC, Technion, NASA/GSFC, Catholic University, ESAC, INAF/Arcetri, UMBC, Strasbourg Observatory)

The present day occurrence and properties of massive black holes in low-mass galaxies serves as a prime observational probe for the black hole population in the early universe. Here, we present a sample of 60 hard X-ray sources stemming from 55 dwarf galaxies selected as possible black hole candidates. This sample had been chosen by cross-matching a sample of 44,594 objects from the NASA-Sloan Atlas (NSA) with masses M_⋆ ⩽3×10⁹ M_⊙ against the X-ray population given in the Chandra Source Catalogue [CSC, Release 2.0]. While the X-ray sources in our sample have luminosities L_2-10keV∼10³³-10⁴⁰erg s^-1, luminosities in this regime may be due to either stellar-mass X-ray binaries or by massive black holes accreting at a low Eddington ratio. Thus, we analyze each of these sources to determine which is the more probable cause. From our analysis, we find that (27%) of our X-ray sources show statistically significant enhanced X-ray emissions when compared to the total contribution of emissions from low and high mass X-ray binaries throughout the galaxy, estimated from the L_{2-10 keV}^XRB-M_⋆-SFR star formation rate relation defined by more massive and luminous systems. This analysis shows that a decent fraction of our X-ray enhanced dwarf galaxies have excess emissions consistent with a nuclear X-ray source, though this is not certain to be the cause. Further observations are required to definitively determine if these sources are caused by stellar-mass X-ray binaries or active galactic nuclei (AGN) powered by more massive black holes.

Co-Authors: Elena Gallo (University of Michigan)

Mergers of elliptical galaxies are likely to create supermassive black hole binaries, with the most promising sites being the giant elliptical galaxies at the centers of clusters of galaxies. We have studied the brightest cluster galaxies in Abell 85 and Abell 1775 in the radio with the JVLA, the X-ray with Chandra, and in the optical to investigate whether the large cores of these galaxies are caused by supermassive binaries, and what the configurations of the central radio sources reveal about feedback processes in these prominent X-ray clusters.

Co-Authors: Omar Lopez-Cruz, Diana M. Worrall (INAOE, University of Bristol)

The highly energetic outflows from Active Galactic Nuclei detected in X-rays are one of the most powerful mechanisms by which the central supermassive black hole (SMBH) interacts with the host galaxy. The last two decades of high resolution X-ray spectroscopy with XMM- Newton and Chandra have substantially improved our understanding of the nature (and impact) of these outflowing ionized absorbers. Here I discuss some landmark results on AGN X-ray outflows studied using Chandra and XMM-Newton and how they changed/improved our concepts about supermassive black hole and host galaxy relations and galaxy evolution. We are now poised to take the next giant leap with higher spectral resolution and higher throughput observatories (Athena, XRISM and Lynx) to understand the physics and impact of these outflows on the host galaxy gas. The future studies on X-ray outflows not only have the potential to unravel some of the currently outstanding puzzles in astronomy, such as the physical basis behind the MBH–σ relation, the cooling flow problem in intra-cluster medium (ICM), and the evolution of the quasar luminosity function across cosmic timescales, but also provide rare insights into the dynamics and nature of matter in the immediate vicinity of the SMBH.

Co-Authors: Matteo Guainazzi (ESTEC (The Netherlands))

As a distinguishing AGN characteristic, fluorescent Fe Kalpha (iron) line emission is routinely interpreted to originate from obscuring material around the SMBH on a few pc scale. Therefore the iron line can be used as an independent tracer to AGN nuclei-obscuration. However, recent spatially resolved Chandra studies indicate the existence of extended iron line emission extending to kpc scale in the host galaxy. The connection between Fe line emission and large-scale gas can be resolved directly only in nearby sources, but could be inferred in more distant AGN by a connection between line emission and star-forming gas and dust. Here we present the results from a stacking analysis and X-ray spectral fitting performed on Chandra Deep Field South 7 Ms catalog (1008 AGNs) and the lastest Chandra Deep Wide Field Survey (∼7000 AGNs). From the average spectra, we found that the strength of the iron line EW(Fe) increases by a factor of 2 with for far-IR luminous galaxies, but has no dependence on stellar mass or X-ray luminosity. This suggests X-ray reflection over large scales (well beyond the torus) in host galaxies may be widespread in distant galaxies.

Co-Authors: Ryan C. Hickox (Dartmouth College)

I will discuss the recent efforts made by Chandra and XMM to search for and characterise the most obscured and Compton thick AGN at moderate (z∼2), up to high (z∼6) redshifts, as obtained by the deepest Chandra and XMM surveys mainly in the CDF. The observational strategy which maximise the scientific return of future Athena surveys with both the Wide Field Imager and with the X-ray Integral Field Unit will be presented.

Co-Authors: Kazushi Iwasawa, Cristian Vignali, Roberto Gilli, Giorgio Lanzuisi, Marcella Brusa (IEEC-UB, DIFA-Unibo, INAF-OAS,INAF-OAS,DIFA-Unibo)

To constrain different formation paths of intermediate-mass (10⁴-10⁶ solar mass) black holes (IMBHs), we measure the average BH accretion rates of the progenitors of present-day dwarf galaxies over the past 9 Gyr using deep Chandra observations in the CANDELS fields and in COSMOS, where a volume-limited sample of progenitors can be traced up to z∼2. Due to the AGN downsizing phenomenon, our results can be used to derive most of the BH mass accumulated via accretion for the dwarf galaxies. This will determine whether the majority of dwarf galaxies can harbor IMBHs grown through typical accretion, or if the existence of IMBHs in the local universe requires massive BH seeds formed via the direct collapse of primordial gas clouds.

Co-Authors: Guang Yang, Niel Brandt, Bret Lehmer, Amy Reines, Fabio Vito (Penn State University, Penn State University, University of Arkansas, Montana State University, Pontificia Universidad Catolica de Chile)

About half of nearby galaxies have surface brightnesses below that of the sky. Compared to "normal" galaxies, these low-surface-brightness galaxies (LSBGs) have lower star formation, fewer companions, and larger gas-mass fractions. Despite their ubiquity, they have barely been explored with X-rays. We present the results of a Chandra survey of nearby LSBGs to search for low-level nuclear activity. After assessing the likelihood of X-ray binary contamination, we find an active fraction of about 15%, which is consistent with the expectations based on the stellar masses of the LSBGs but not their total mass. This indicates that the massive black holes in LSBGs evolve with their stellar populations. This work also shows that LSBGs are an important population for future surveys of nuclear activity to determine the local occupation fraction of massive black holes, such as those that can be carried out with Lynx.

Co-Authors: Elena Gallo, Anil Seth, Jenny Greene, Vivienne Baldassare (University of Michigan, University of Utah, Princeton University, Yale University)

NGC 3783 is one of the brightest Sy 1 AGN observed by Chandra, offering one of the richest troves of HETG data in the archive. These spectra depict a forest of absorption lines from a multi-phase outflowing wind, as well as underlying emission signatures from reflection off of distant and inner disk gas. The >1Msec of available HETG archival spectra has informed the modeling of many subsequent datasets, including those from XMM-Newton, Suzaku and NuSTAR. Combining the results of these observing campaigns has yielded new insights into the primary continuum, absorption and reprocessed emission components in NGC 3783. Here we report on the results of these spectral modeling studies and also discuss their implications on our understanding of the corona, the spin of the supermassive black hole, and the structure of the absorbing gas in this bright, nearby AGN.

Co-Authors: Michael Nowak, Christopher Reynolds (Washington University St. Louis, Cambridge University)

Spin measurements of supermassive black holes (SMBH) provide crucial constraints on the accretion processes that power active galactic nuclei (AGN) and fuel outflows. However, spin measurements are mainly limited to a few dozen nearby sources for which high quality, high signal spectra (e.g., from Chandra, XMM, NuSTAR) are available. Here I will present our stacking analysis in which we measure the average SMBH spin of ∼2000 AGN in the Chandra-COSMOS Legacy survey. We find broad Fe Kα line emission in the average COSMOS spectra, to which we fit a relativistic line profile and determine the magnitude of the spin. The sample size and resolution of the COSMOS Legacy field also provides a unique environment to investigate the average spin as a function of other observables (e.g., redshift, luminosity) up to z∼5.3. The results of this work will provide insight into the physical mechanisms governing AGN growth and feedback, and improve our understanding of the black hole-galaxy connection.

Co-Authors: Francesca Civano, Laura Brenneman, Giorgio Lanzuisi, Stefano Marchesi (Center for Astrophysics | Harvard & Smithsonian, Center for Astrophysics | Harvard & Smithsonian, INAF-OABO, INAF-OABO)

Active galactic nucleus (AGN) pairs are a crucial laboratory to study the effects of galaxy merger in the standard paradigm of galaxy formation and evolution. We present a Chandra archival survey of candidate AGN pairs  at median redshift ∼0.1, which were systematically identified from the Sloan Digital Sky Survey with projected separations rp < 100 kpc and velocity offsets <600 km s^-1. Out of the 1286 AGN pairs, we find 67 pairs with Chandra observations, making it currently the largest sample of AGN pairs studied in the keV X-ray band. The X-ray incidence rate is significantly higher than in the control sample of star-forming galaxy pairs which do not exhibit optical AGNs in their center and single AGNs, lending support to the optical AGN selection. The X-ray luminosity increases with decreasing projected separation in AGN pairs for rp > 10 kpc, suggesting an enhancement of central BH activity,  while it decreases when rp < 10 kpc, which may be caused by obscuring, merger-induced gas inflows; alternatively, this may signature the later stage of merger where AGN activity is substantially reduced, as predicted by numerical simulations.

Co-Authors: Meicun Hou, Zhiyuan Li, Xin Liu (Nanjing University, University of Illinois at Urbana-Champaign)

We report the discovery of SDSS J0849+1114 as the first triple type-2 Seyfert nucleus known, representing three active black holes identified from new, spatially resolved optical slit spectroscopy using the Dual Imaging Spectrograph on the 3.5m telescope at the Apache Point Observatory. We also present new, complementary observations including the Hubble Space Telescope Wide Field Camera 3 U- and Y-band imaging, Chandra Advanced CCD Imaging Spectrometer S-array X-ray 0.5-8 keV imaging spectroscopy, and NSF's Karl G. Jansky Very Large Array radio 9.0 GHz imaging in its most extended A configuration. These comprehensive multiwavelength observations, when combined together, strongly suggest that all three nuclei are AGN. While still at kpc-scale separations where the host-galaxy gravitational potential dominates, the black holes may evolve into a bound triple system in ≲2 Gyr. Such triple merger systems may explain the overly massive stellar cores observed in some elliptical galaxies such as M87 and are expected to be unique gravitational wave sources. Similar systems may be more common in the early universe when galaxy mergers are thought to be more frequent.

Co-Authors: Xin Liu, Zhiyuan Li, Kristina Nyland, Hengxiao Guo, Minzhi Kong, Yue Shen, Joan M. Wrobel, Sijia Peng (University of Illinois at Urbana-Champaign, Nanjing University, National Research Council, University of Illinois at Urbana-Champaign,Hebei Normal University, University of Illinois at Urbana-Champaign, National Radio Astronomy Observatory, Nanjing University)

Chandra has conducted over 30 extragalactic surveys, at depths between 100 ks to 7 Ms that cumulatively add up to several years of observations. This has led to the discovery of thousands of distant black holes and hundreds of refereed papers that have defined our current understanding of the growth of supermassive black holes (SMBHs), their radiative outputs, and their host galaxies. These surveys, however, remain highly biased against heavily obscured AGN, whose emission peaks at 20-30 keV. Moreover, as the vast majority of the deep field Chandra sources are at z>0.5 it is very difficult to find dual, recoiling, and offset AGN associated with galaxy mergers, and to resolve jets, study AGN feedback, and look for extended profiles of plasma (Fe Kα) emission. Here we will highlight some of our initial results on black hole growth in galaxy mergers from our cool attitude program and sub kpc dual AGN.

Chandra's exquisite angular resolution and low background make it ideal for deep survey science. And powerful new discoveries await for Chandra via observations optimized for new observatories that can take full advantage of these strengths. We have begun to develop a planned JWST field, the North Ecliptic Pole Time Domain Field (NEP-TDF). The JWST-NEP-TDF will ultimately provide the deepest possible JWST complement to Chandra data, and will open up new opportunities for deep time domain science that complements the wide-field time domain revolution. We will discuss survey design, multi-wavelength components, recent results, and future prospects for this unique field.

Co-Authors: Rogier Windhorst, Norman Grogin, Martin Elvis, Francesca Civano, Nico Cappelluti, Rolf Jansen, Anton Koekemoer, Guenther Hasinger, Seth Cohen, Walter Brisken, Rick Perley, James Condon, Matt Ashby, Giovanni Fazio, Chelsea Macleod (Arizona State University, STScI, Center for Astrophysics | Harvard and Smithsonian, Center for Astrophysics | Harvard and Smithsonian, University of Miami, Arizona State University, STScI, ESA, Arizona State University, NRAO, NRAO, NRAO, Center for Astrophysics | Harvard and Smithsonian, Center for Astrophysics | Harvard and Smithsonian, Center for Astrophysics | Harvard and Smithsonian)

Giga-Hertz Peaked Spectrum (GPS) and Compact Steep Spectrum (CSS) radio sources comprise a population of compact objects with radio emission fully contained within the innermost regions of the host galaxy (< a few kpc). Spectral and kinematic age measurements indicate their young age (typically < thousands years, and in some cases less a few hundred years). These sources provide important insights to the initial phase of the jet formation, radio source growth, source evolution, and the jet impact on the ISM in the very central regions of the host galaxy. Over the last two decades we used Chandra to study the X-ray properties of these sources. Because these sources are relatively faint in X-rays only a few sources have been detected by other X-ray missions before Chandra. We have obtained Chandra and XMM-Newton observations for a large sample of these radio sources over several observing cycles. Our most recent Chandra observations targeted Compact Symmetric Objects (CSO) associated with the nuclear regions of nearby galaxies, and a small sample of MHz-peaked sources constituting the first X-ray sample of young radio sources at high redshift.

Chandra has revolutionized the X-ray study of resolved quasar jets but, even after 20 years, important issues remain unsettled. Despite the fact that kpc-scale inverse-Compton scattering of cosmic microwave background photons into the X-ray band is mandated, proof of its detection in individual sources is often insecure. High redshift should provide favorable conditions for detection, and importantly allows us to constrain the known synchrotron-emitting electron component at high energies. We present results for the resolved jet in the high-redshift quasar PKS J1421-0643 that argue in favour of the detection of inverse-Compton X-rays for modest magnetic field strength, Doppler factor, and viewing angle.

Co-Authors: Mark Birkinshaw, Dan Schwartz, Herman Marshall, John Wardle, Aneta Siemiginowska (University of Bristol, Harvard-Smithsonian Center for Astrophysics, Kavli Institute for Astrophysics and Space research M.I.T., Brandeis University, Harvard-Smithsonian Center for Astrophysics)

Despite their intrinsically bright, multi-wavelength emission, an unknown fraction of active galactic nuclei (AGN) remain obscured, their nuclei invisible due to orientation-dependent obscuration by massive amounts of material. One way to select AGN samples that are orientation-unbiased (although limited to radio-loud sources) is low frequency radio, where the selection is based on extended, optically thin radio lobes. Radio data also provide an independent estimate of orientation via the radio core fraction.

We extend our studies of a complete, 178 MHz radio flux-limited, Chandra observed sample of high-redshift (1<z<2) 3CRR sources (Wilkes et al. 2013) to medium redshifts (0.5<z<1). This complete, orientation unbiased sample of bright, FRII radio sources includes 36 objects: quasars, narrow-line radio galaxies (NLRGs) and 1 low-excitation radio galaxy (LERG), all with matched radio luminosities (log L(178MHz)∼35.5-36.5$). We find that the properties of the medium-z 3CRR sample, similarly to the high-z sample, are broadly consistent with the orientation-dependent obscuration of the Unification model: quasars viewed face-on to the central engine are X-ray bright, unobscured, and have soft X-ray emission. NLRGs, on the other hand, viewed edge-on are X-ray faint, obscured, and generally show harder X-ray emission. However, the sample includes a new population, not seen at high redshift: NLRGs with low column densities (log N_H<22) and viewing angles skimming the edge of the dusty torus. These sources are bright in X-rays, have soft hardness ratios, and weak near-to-mid-IR emission suggesting low L/Ledd ratios resulting in clumpier and cooler torus. 22% of sample show Compton-thick L([OIII])/L(2-8keV) ratios (similar to the high-z 3CRR sample).

Co-Authors: Joanna Kuraszkiewicz, Belinda J. Wilkes, Adam Atanas, Johannes Buchner, Martin Haas, Peter Barthel, S. P. Willner, D. M. Worrall, Mark Birkinshaw, Robert Antonucci, M.L.N. Ashby, Mojegan Azadi, Rolf Chini, G.G.Fazio, Charles Lawrence, Patrick Ogle (0.0)

Here we present the analysis of the Chandra ACIS−I data for the two peculiar and nearby radio galaxies CGCG 292−057 (z=0.054) and CGCG 292-233 (z=0.01075). The former system, hosted by a post-merger bulge-dominated galaxy with a LINER type nucleus, is characterized by a complex radio morphology, consisting of arc-second scale inner lobes extending for about 20kpc, and embedded within the arcmin-scale outer radio halo. The latter system, hosted by an elliptical galaxy in a non-interacting pair, again with the LINER-type nucleus, possesses an extremely compact, mas-scale double-lobe structure with the projected extent of a few parsecs, indicative of the newly born jets. The two sources represent therefore different snapshots of the intermittent jet activity in low-power AGN, which we can study in detail with unprecedented angular resolution of ACIS−I. We observed CGCG 292−057 with Chandra for 93 ksec, and here we present the final results of the data analysis and modelling. For CGCG 292-233, we present an analogous analysis of the archival and previous unpublished 40 ksec-long Chandra exposure. For both targets, we performed detailed PSF simulations that allowed us to investigate the surface brightness profiles of the X-ray emission, and hence to properly extract the spectra of the unresolved nuclei, gaseous envelopes of host galaxies, and the backgrounds. Due to the low photon statistics (several hundreds of counts within the 0.5-7.0 keV range in both cases), thus selected spectra were then modelled (together with the background) by applying the Poisson likelihood (Cstat), and assuming different emission scenarios (including the absorbed power law, the multi-temperature thermal plasma, etc.). In this way, we have robustly determined the main parameters of the studied systems, including (i) the X-ray luminosities of the unresolved nuclei, (ii) the temperatures and pressures of the hot gaseous fraction of the interstellar medium, and (iii) peak energies and equivalent widths of the fluorescence iron lines, indicative of the X-ray reflection in the sources from neutral or ionized absorbers. All of these, in turn, allow us to discuss the energetics of the newly born jets, and the properties of the ambient medium interacting directly with compact radio lobes on galaxy scales.

Co-Authors: Karthik Balasubramaniam, Lukasz Stawarz, Volodymyr Marchenko, Malgorzata Sobolweska, C. C Cheung, Aneta Siemiginowska, Marek Jamrozy, Dorota-Koziel Wierzbowska, Arti Goyal, Rameshan Thimappa (Astronomical Observatory of the Jagiellonian University, ul. Orla 171, 30−244 Kraków, Poland, Astronomical Observatory of the Jagiellonian University, ul. Orla 171, 30−244 Kraków, Poland, Astronomical Observatory of the Jagiellonian University, ul. Orla 171,30−244 Kraków, Poland, Harvard Smithsonian Center for Astrophysics, 60 Garden St, Cambridge, MA 02138, USA, Space Science Division, Naval Research Laboratory, Washington, DC 20375−5352, USA, Harvard Smithsonian Center for Astrophysics, 60 Garden St, Cambridge,MA 02138, USA, Astronomical Observatory of the Jagiellonian University, ul. Orla 171, 30−244 Kraków, Poland, Astronomical Observatory of the Jagiellonian University, ul. Orla 171, 30−244 Kraków, Poland, Astronomical Observatory of the Jagiellonian University, ul. Orla 171, 30−244 Kraków, Poland, Astronomical Observatory of the Jagiellonian University, ul. Orla 171, 30−244 Kraków, Poland)

Two selected regions (≃1/3 \times 1/3° each) within the Southern giant radio lobe of Centaurus A radio galaxy have been previously mapped in X-rays with the Suzaku's X-ray Imaging Spectrometer (Stawarz et al. 2013). These studies have been followed up with five Chandra pointings, targeting the two Suzaku’s fields in the Southern lobe, and also three analogous regions selected within the Northern lobe. Here we present the preliminary results of the analysis of these Chandra data, totalling to 97ks exposure. First, we identify all the point sources detected with the ACIS instrument. We search for the optical and infrared counterparts of those sources in the available catalogs and provide a simple analysis of their X-ray spectra using the Bayesian Estimation of Hardness Ratio. Next, we analyze the diffusive emission component filling the entire FOV of the instrument (after removing the point sources). For this purpose, we apply the novel method of a "covariance mapping", resulting from correlating the spectra extracted from various parts of the Chandra image. We discuss how our preliminary results enable one to differentiate between the emission components related to the giant radio lobes, and those representing the foreground/background objects, as well as a diffuse continuum originating from outside the lobes.

Co-Authors: Karthik Balasubramaniam, Lukasz Stawarz, Volodymyr Marchenko (Astronomical Observatory of the Jagiellonian University, ul. Orla 171, 30−244 Kraków, Poland, Astronomical Observatory of the Jagiellonian University, ul. Orla 171, 30−244 Kraków, Poland,Astronomical Observatory of the Jagiellonian University, ul. Orla 171, 30−244 Kraków, Poland)

Reported in the literature are at least a few Chandra detected extragalactic jets which show significant offsets between X-ray and radio emission. These offsets have occurred in jets with a wide range of radio powers. Despite this fact, various single-zone emission models were put in place to explain the X-ray emission from the jets. We have undertaken a detailed study of all the Chandra X-ray jets detected to date and we are finding that these offsets are more the norm than an exception. This questions the applicability and conclusions of single-zone models.

Co-Authors: Karthik Reddy Solipuram, Markos Georganopoulos, Eileen Meyer (University of Maryland Baltimore County, NASA Goddard Space Flight Center)

We present results of spectral energy distribution analysis for radio loud quasars from the 3CRR sample at 1<z<2. We consider a multi-component model to fit the photometry over a wide range of wavelengths from X-ray to radio. The components at the highest energies account for the X-ray, UV and optical emission from the AGN’s accretion disk and the corona. To account for the MIR emission from the dust grains surrounding the central engine we consider a combination of a clumpy medium and a homogeneous dusty disk. To model the emission from the radio jets and lobes we consider a power-law/parabola component. In addition, an underlying component from UV to radio wavelengths is considered which accounts for the emission from stellar populations, cool dust and star formation in the host galaxy. Using this multi-component analysis, we investigate the physical properties of these quasars as well as their host galaxies. In addition, we investigate the relationship between AGN activity and their host galaxies star formation rate and between the level of obscuration of AGN and their host galaxies physical properties.

Co-Authors: Belinda Wilkes (1), Joanna Kuraszkiewicz(1), Ralf Siebenmorgen(2), Peter Barthel(3), Martin Haas(4), Diana Worrall(5), Mark Birkinshaw(5), Steven Willner (1) Matthew Ashby (1), Jonathan McDowell (1) (1) Harvard-Smithsonian Center for Astrophysics2) European Southern Observatory3) University of Groningen4) Ruhr University Bochum5) University of Bristol)

Cygnus A is the archetype of powerful Fanaroff-Riley class II radio galaxies. A very deep Chandra image of its radio cocoon clearly reveals thermal X-ray emission from the envelope of shock compressed gas and nonthermal emission from the hotspots and radio lobes. A surface brightness profile of the lobe shows that the X-ray emission coefficient peaks on our line of sight within the lobe, where the X-ray emission is due to inverse Compton scattered radio synchrotron and microwave background photons. A nearly circular "hole" with a radius of ∼3.5 kpc surrounds primary hotspot E in the eastern radio lobe. The X-ray deficit implies that there is a hole in the radio lobe, with a depth of about twice its diameter. We argue that the eastern radio jet has run into the shocked intracluster medium at hotspot E, where it is also shocked and deflected back into the radio lobe. The hole in the lobe is carved by the shocked jet plasma as it expands and flows out of the hotspot on its way to the larger, brighter secondary hostspot, D. Such an intepretation disfavors the dentist drill model for multiple hotspots. The absence of a corresponding feature in the west is likely a consequence of Doppler beaming.

Co-Authors: Bradford Snios, Amalya Johnson, Ralph Kraft, John ZuHone, Michael Wise, Brian McNamara (CfA, Columbia, CfA, CfA, SRON, Waterloo)

ClusterPyXT is a new software pipeline to generate spectral temperature, X-ray surface brightness, pressure, density, and entropy maps from Chandra X-ray observations of galaxy clusters. These data products help to elucidate the physics of processes occurring within clusters of galaxies, including turbulence, shock fronts, nonthermal phenomena, and the overall dynamics of cluster mergers. ClusterPyXT automates the creation of these data products with minimal user interaction and allows for rapid analyses of Chandra archival data with user defined parameters and the ability to straightforwardly incorporate additional observations. This poster will describe the use of this code and the updated features since publication including the new graphical user interface. ClusterPyXT is an open source on GitHub written in Python 3 and makes extensive use of CIAO 4.11.

Co-Authors: Brian Alden, Eric Hallman, David Rapetti, Jack Burns, Abhirup Datta (CU Boulder, CU Boulder, CU Boulder, CU Boulder, Indian Institute of Technology - Indore)

SpARCS104922.6+564032.5 is one of the most massive and extreme galaxy clusters known to date. It stands out as harboring a still assembling brightest cluster galaxy (BCG) undergoing extreme stellar formation at z=1.7091 (∼850 M_⊙/year). We present the first X-ray images for the cluster. Our 170 ks (≈50 hour) of Chandra observations are groundbreaking not only due to the exceptional nature of the cluster but also because the object is the first of its ilk to ever be imaged so deeply in the X-rays. Using several techniques for calculating galactic substructure and proxies of cooling flows, we develop a more coherent image of the mechanism responsible for the rampant stellar formation surrounding the BCG. Since the SpARCS cluster is positioned at a pivotal epoch in our cosmological history, these results have direct consequences for our understanding of how the most massive over densities in the Universe form and evolve with time.

Co-Authors: Julie Hlavacek-larrdondo, Tracy Webb, Adam Muzzin, Michael McDonald, Gillian Wilson (0.0)

Cooling of the hot, gaseous intracluster medium in cluster centers can feed the supermassive black holes in the cores of the dominant cluster galaxies leading to active galactic nucleus (AGN) outbursts. This AGN feedback can reheat the gas, stopping cooling and large amounts of star formation. Most relaxed, cool core clusters host powerful AGN in their central galaxies and these AGN can significantly affect the distribution of e.g., temperature and abundance on cluster scales. AGN heating can come in the form of shocks, buoyantly rising bubbles that have been inflated by radio jets and lobes, and sound wave propogation. Sloshing of the cluster gas, related to minor, off-center interactions with galaxy sub-clusters or groups also affects the distribution of temperature and abundance on large scales. This sloshing gas can interact with the AGN's radio-emitting jets and lobes causing them to bend. This bending is also found in AGN jets and lobes embedded in clusters undergoing major, head-on cluster, cluster mergers. Since this bending is a signature of interaction within clusters, bent, double-lobed AGN observed in the radio can be used as beacons for clusters of galaxies at high redshifts. I will show examples of detailed observations of nearby clusters and AGN during Chandra's first twenty years. In addition, I will present X-ray follow-up observations of distant clusters discovered using our large sample of high-redshift, bent-double radio sources that were also observed at infrared and optical wavelengths ("COBRA,"Clusters Occupied by Bent Radio AGN).

Co-Authors: R. Paterno-Mahler, E. Golden-Marx, M. Brodwin, M. Ashby, J. Wing, E. Douglass, S. Randall, C. Sarazin, T. Clarke, B. McNamara (Keck Science Center, BU, U. Missouri KC, CfA, CfA, Farmingdale State SUNY, CfA, UVA, NRL, U. Waterloo)

In the current picture of hierarchical structure formation, galaxy groups play a vital role as the seeds from which large assemblies of matter form. Compact groups are also important environments in which to watch the fueling of star formation and AGN activity, as the conditions are ideal for galaxy-galaxy interactions. We have identified a galaxy system that may represent an intermediate or transition stage in group evolution. Shakhbazyan 1 (or SHK 1) is a remarkably compact collection of about ten massive, red-sequence galaxies within a region 100 kpc across. Deep optical observations reveal a very extended envelope of stars surrounding the galaxies, indicating a large amount of intra-group starlight and evidence that the galaxies are dynamically interacting. Chandra spectral imaging confirms the presence of a hot, diffuse intra-group medium (IGM), with a hydrostatic mass about 1/3 that expected from the optical richness. Multi-object spectroscopy in turn reveals a complicated, multi-modal velocity structure and signatures of AGN activity from several of the central galaxies. These results suggest that this system may be in a transition stage of galaxy merging, similar to that expected in the formation of a fossil group. Alternatively, SHK 1 may consist of multiple poor groups in the final stages of merging along our line of sight. We explore these scenarios and outline paths of future study for this enigmatic system.

Co-Authors: Eric D. Miller, Michael McDonald, Matthew Bayliss, Marshall Bautz, Catherine Grant, Saul Rappaport, Sylvain Veilleux (MIT, MIT, MIT, MIT, MIT, MIT, U. Maryland)

We present deep Chandra, XMM-Newton, GMRT and Hα observations of the high-velocity group-group merger NGC 6338. X-ray imaging and spectral mapping show that as well as trailing tails of cool, enriched gas, the two cores are embedded in a ∼250 kpc-wide region of shock heated gas with temperatures rising to ∼5 keV. The merger is occurring primarily along the line of sight, with a velocity difference of ∼1400 km/s between the dominant ellipticals. We estimate that the collision has produced shocks of Mach 2.3-3.1, making this one of the most violent mergers yet observed between groups. We show that both group cores host potential AGN cavities and Hα nebulae, indicating rapid cooling. In the southern core around NGC 6338 we observe co-spatial X-ray and Hα filaments, whose X-ray components have very low entropies (<10 keV cm^-2) and short cooling times (200-300 Myr). The northern core is crossed by a bar of dense, cool X-ray gas with an Hα cloud at one end, offset from the dominant galaxy, suggesting that ram-pressure has disrupted the connection between IGM cooling and the central AGN. Despite the disturbance caused by the merger, we find reasonable agreement between hydrostatic and Sunyaev-Zel'dovich mass estimates. Both show the combined system mass to be of order 10¹⁴ M_⊙, implying that the result of this group-group merger will be a galaxy cluster.

Co-Authors: Gerrit Schellenberger, D J Burke, Ming Sun, Jan M Vrtilek, Laurence P David, Craig Sarazin (CfA, CfA, University of Alabama, CfA, CfA, University of Virginia)

Galaxy groups are arguably the most important environment for our understanding of galaxy evolution, AGN feedback and the development of the hot intergalactic medium (IGM). Previous studies of groups in the nearby universe have either used optically-selected samples to examine galaxy populations, or X-ray selected samples (mainly derived from the ROSAT All-Sky Survey) to examine IGM properties. While these approaches have yielded important results, their selection methods mean they are subject to significant biases. We have created the the Complete Local-Volume Groups Sample (CLoGS), an optically-selected statistically-complete sample of 53 groups in the nearby Universe (D<80 Mpc), surveyed in the X-ray (Chandra and/or XMM-Newton), low-frequency radio (GMRT 235 & 610 MHz) and, for the dominant galaxies, molecular gas (IRAM 30m or APEX CO). This combination of data allows us to confirm which groups are fully virialized, examine their dynamical and thermal state, and investigate the role of AGN feedback in these systems. We will present results from the sample, showing that roughly one third of X-ray bright groups in the local universe are dynamically active (merging or sloshing), and roughly one third show evidence of ongoing or recent feedback from central AGN. We will examine the conditions under which feedback occurs in groups, and show examples of powerful outbursts which may dramatically over-heat the IGM. We will also show that a significant fraction (>30%) of the nearby group population has been missed by previous studies, and discuss the implications for future surveys.

Co-Authors: Konstantinos Kolokythas, Jan M Vrtilek, Laurence P David, Gerrit Schellenberger, Simona Giacintucci, Arif Babul, Soamk Raychaudhury, Myriam Gitti (North-West University (South Africa), CfA, CfA, CfA, Naval Research Laboratory, University of Victoria, IUCAA, University of Bologna)

The vast majority of the detailed analyses of ICM astrophysical processes have been focused on z<1 clusters observed primarily in X-ray. These studies provided valuable constraints on a plethora of mechanisms such as gas cooling, AGN feedback, the physics behind cold and shock fronts, or merger dynamics. However, the most active part of galaxy cluster formation is assumed to be carried out at redshifts 1<z<2. In order to study the progenitors of the well-known clusters at z<0.1, it is essential to probe the evolution of the radial distributions of all the ICM thermodynamic properties in low mass systems at z>1. However, the required exposures to make such analyses with the current X-ray observatories are extremely large and usually prevent such studies to be conducted. Furthermore, the next generation of X-ray observatories such as Athena and Lynx will only come into play in the 2030’s. Therefore, it is essential to propose new techniques to study the evolution of the intracluster medium properties at z>1.The South Pole Telescope has provided us with a large sample of nearly mass selected galaxy clusters up to z = 1.7. SPT clusters are detected through the SZ effect whose amplitude depends on the ICM pressure distribution along the line of sight. We have combined the SPT SZ maps of a sample of 18 clusters at 0.8<z<1.4 with low-SNR Chandra data. As X-ray surface brightness is mainly sensitive to the ICM density distribution along the line of sight, the joint analysis of Chandra and SPT data enables us to estimate all the ICM thermodynamic properties of these clusters. We further interpret these results given the morphological constraints that we can establish at small and large scales using the Chandra and SPT maps. This analysis paves the way to an in-depth characterization of the distant progenitors of Perseus and Abell-like clusters.

Co-Authors: M. McDonald, M. Bautz, L. Bleem, B. Benson (MIT, MIT, University of Chicago, University of Chicago)

Galaxy clusters are the largest known virialized structures in the Universe and are therefore not only the largest physical laboratories in the Universe, galaxy clusters also inform and help constrain cosmology. The low surface brightness regions of galaxy cluster outskirts, beyond r₅₀₀, seem to depart from hydrostatic equilibrium most likely due to cold gas clumps at large cluster radii, weakening accretion shocks, turbulence and cosmic rays, non-thermal pressure support from bulk motions, and electron-ion non-equilibrium. Galaxy clusters form and merge along and at the nodes of large-scale intercluster filaments. X-ray telescopes, particularly Suzaku with it’s low and stable particle background and more recently with increased time dedication from Chandra and XMM-Newton, have made it possible to reliably study galaxy cluster outskirts as far out as r₂₀₀, where the outskirts meet and start to most noticeably, thus far, interact with the large-scale intercluster filament environment. These new studies in the X-ray are starting to shed light on cluster formation and enrichment scenarios, and on whether the departures, or non-departures, from hydrostatic equilibrium are correlated with the presence of intercluster filaments and the underlying thermodynamic processes that occur in this interface region. These relatively new studies will be discussed, with a focus on the more recent results of the Abell 3391/Abell 3395 intercluster filament and the Abell 98 intercluster filament.

Co-Authors: Scott Randall, Yuanyuan Su, Herve Bourdin, Christine Jones, Kelly Holley-Bockelmann (CfA, Kentucky University, INAF, CfA, Vanderbilt University)

Hydrostatic cluster masses together with the halo mass function have been shown to be a competitive, cosmological tool, since they can be derived from X-ray observations alone for large samples and with high precision. Biases from non-thermal pressure can be quantified and corrected for high mass objects. However, cosmological studies including galaxy groups suffer from unknown selection effects.

We investigate those biases using the largest, complete X-ray sample of the brightest clusters and groups available. We quantify the luminosity-temperature scaling relation with more than 300 objects over a large range of masses, out to redshift 0.4, and find that the intrinsic scatter has a non-uniform distribution.

We select a subset of the most relaxed and most disturbed objects and show, that the scatter in these subsamples is reduced, but the non-uniform distribution remains. Taking into account selection effects, we show constraints on cosmological parameters when only the temperatures of clusters and groups are known. This is of particular interest also for eROSITA, since the first survey catalog will be dominated by the brightest objects already analyzed here.

Co-Authors: Konstantinos Migkas, Thomas Reiprich, Lorenzo Lovisari, Florian Pacaud, Miriam Ramos, Jan Vrtilek, Laurence David, Ewan O'Sullivan (Bonn University, Bonn University, SAO, Bonn University, MPE, SAO, SAO, SAO)

Over the past 20 years, Chandra has revealed in exquisite detail the thermodynamic and chemical properties of the hot plasma in clusters of galaxies. Chandra observations continue to challenge and inform simulations of galaxy clusters and cluster mergers, especially given the fact that the spatial resolution of the former is often finer than the latter. Longer exposures have also provided more details which have been used to constrain simulations. I will present recent results in this area in which Chandra observations and simulations have been combined to discern the physical properties of the cluster plasma and also probe the properties of the dark sector.

We report Chandra observations of the environment of the unusual redshift 1 quasar PG1407+265, first studied in X-rays by the Einstein Observatory. We discuss a new $10^44$ erg/s X-ray cluster found 1 arcminute from it. We discuss the 4-decade, factor 10 X-ray variability of the quasar. We present preliminary spectroscopy of the X-ray cluster gas and optical spectroscopy of the cluster galaxies, both of which indicate that it has z=0.68

Co-Authors: Aneta Siemiginowska , Kathleen Blundell, Luigi Gallo (CfA, Oxford, St Mary's U.)

X-rays provide a unique window into the properties of young stellar populations, as they probe populations of accreting high mass binaries. Observations in the local universe and in deep fields have explored the relationship between star formation and X-ray emitting binary populations, but X-ray observations of the most highly magnified, strongly lensed galaxies have represented an unexplored frontier. X-ray studies of bright giant arcs can provide critical constraining on the properties of the stellar populations---especially the high mass stars and the high end of the initial mass function---on sub-galactic scales. The lensing magnification allows us to distinguish the X-ray properties of physically distinct star forming regions, which can span a wide range in metallicity, age, and stellar mass. We have recently combined strong lensing and deep Chandra observations to serendipitously detect, and spatially resolve, the X-ray emission associated with ongoing star formation in a highly magnified, strongly lensed dwarf star-forming galaxy. This result paves the way for future work that will exploit strong lensing magnification and the Chandra X-ray Observatory to perform spatially resolved X-ray diagnostics of star formation and stellar populations in the distant universe.

Co-Authors: Michael McDonald, Keren sharon, Mike Gladders, Michael Florian, John Chisholm, Håkon Dahle, Guillaume Mahler, Rachel Paterno-Mahler, Jane Rigby, Emil Rivera-Thorsen, Kate Whitaker (MIT, Michigan, University of Chicago, NASA Goddard, UC Santa Cruz, University of Oslo, Michigan, Claremont McKenna College, NASA Goddard, University of Oslo, UMass-Amherst)

We present new, deep (245 ks) Chandra observations of the galaxy cluster Abell 1664 ($z=0.1283$). These images reveal rich structure, including elongation and accompanying compressions of the X-ray isophotes in the NE-SW direction, suggesting that the hot gas is sloshing in the gravitational potential. This sloshing has resulted in cold fronts, at distances of 50, 110 and 325 kpc from the cluster center. Our results indicate that the core of Abell 1664 is highly disturbed, as the global metallicity and cooling time flatten at small radii, implying mixing on a range scales. The central AGN appears to have recently undergone a mechanical outburst, as evidenced by our detection of cavities. These cavities are the X-ray manifestations of radio bubbles inflated by the AGN, and may explain the motion of cold molecular clouds previously observed with ALMA. The estimated mechanical power of the AGN is $(1.1 \pm 1.0) \times 10^{44}$ erg s$^{-1}$, which may be enough to drive the molecular gas flows, and offset the cooling luminosity of the ICM ($L_{\rm cool} \sim 1.53 \times 10^{44}$ erg s$^{-1}$). This mechanical power is orders of magnitude higher than the measured upper limit on the X-ray luminosity of the central AGN, suggesting that its black hole may be extremely massive and/or radiatively inefficient. We map temperature variations on the same spatial scale as the molecular gas, and find that the most rapidly cooling gas is mostly coincident with the molecular gas reservoir centered on the BCG’s systemic velocity observed with ALMA and may be fueling cold accretion onto the central black hole.

Co-Authors: Michael Calzadilla, Helen Russell, Michael McDonald, Andy Fabian, Stefi Baum, Francoise Combes, Megan Donahue, Alastair Edge, Brian McNamara, Paul Nulsen, Chris O'Dea, Raymond Oonk, Grant Tremblay, Adrian Vantyghem (0.0)

We present a machine-learning (ML) approach for estimating galaxy cluster masses from Chandra mock images. We utilize a Convolutional Neural Network (CNN), a deep ML tool commonly used in image recognition tasks. The CNN is trained and tested on our sample of 7896 Chandra X-ray mock observations, which are based on 329 massive clusters from the IllustrisTNG simulation. Our CNN learns from a low resolution spatial distribution of photon counts and does not use spectral information. Despite our simplifying assumption to neglect spectral information, the resulting mass values estimated by the CNN exhibit small bias in comparison to the true masses of the simulated clusters (−0.02 dex) and reproduce the cluster masses with low intrinsic scatter, 8% in our best fold and 12% averaging over all. In contrast, a more standard core-excised luminosity method achieves 15%─18% scatter. We interpret the results with an approach inspired by Google DeepDream and find that the CNN ignores the central regions of clusters, which are known to have high scatter with mass.

Co-Authors: John ZuHone, Daniel Eisenstein, Daisuke Nagai, Alexey Vikhlinin, Lars Hernquist, Federico Marinacci, Dylan Nelson, Ruediger Pakmor, Annalisa Pillepich, Paul Torrey, Mark Vogelsberger (0.0)

Since the first non-thermal detections of inverse Compton (IC) emission in galaxy clusters at hard X-ray energies, we have yet to unambiguously confirm IC in follow-up observations. Claims of large IC fluxes from the 10' extent of Abell 2163, a massive merging cluster at z = 0.2, make it the next best chance of confirming a previous IC detection with NuSTAR. Additionally, recently available deep XMM data indicate extreme temperature variations (10-20 keV), the hottest of which are likely due to shocks. However, the XMM spectra suffer from variable Galactic absorption across the cluster, which can be avoided with NuSTAR's harder energy band. We find that the global NuSTAR spectrum is consistent with pure thermal emission, with a global temperature of $kT = (11.77 \pm 0.13)$~keV. Our model provides a constraint on IC emission of $1.62 \times 10^{-12}$~erg~s$^{-1}$~cm$^{-2}$ as well as a value for the magnetic field of the cluster, B $>$ 0.22 $\mu$G or B $>$ 0.35 $\mu$G using the normalization obtained from a nine temperature model.

Co-Authors: Daniel Wik, Qian Wang (University of Utah)

The analysis of the cluster environment is a valuable instrument to investigate the origin of AGN and star-forming galaxies gas fuelling and trigger mechanisms. To this purpose, we present a detailed analysis of the point-like X-ray sources in the Bullet cluster field. Thanks to ∼600 ks Chandra observations, we produced a catalog of 381 X-ray point sources up to a distance of ∼1.5 virial radius and with flux limits ∼1×10^-16 and ∼8×10^-16 erg cm^-2 s^-1 in the 0.5-2 keV and 2-10 keV bands, respectively. We identified optical (R band) and infrared (Spitzer/IRAC) counterparts for ∼84% and ∼48% of the X-ray sources, respectively. We obtained new spectroscopic redshifts for 106 X-ray sources and collected from the literature additional 13 spectroscopic and 8 photometric redshifts of X-ray sources. 29 of these X-ray sources have a redshift consistent with that of the Bullet cluster. Spectroscopic and photometric redshifts of infrared sources have been also collected and used as ancillary sample. We used the multi-wavelength data to characterise the nature of the Bullet cluster X-ray point sources. We found a strong (up to a factor 1.5-2) and significant (≥4σ) over-density in both cluster inner region (0.3R₂₀₀<R<0.66R₂₀₀) and external regions, up to ∼1.5R₂₀₀. The over-density in the region 0.66R₂₀₀<R<R₂₀₀ is mostly due to X-ray bright AGN associated to the cluster, while that in the more external region is probably mostly due to field AGN at redshift higher than that of the Bullet cluster. The over density in the inner region is probably due mostly to obscured AGN and active star-forming galaxies. Finally, the spatial distributions of AGN and star-forming galaxies, selected also thanks to their infrared emission, appear similar, thus suggesting that both are triggered by the same mechanism.

Co-Authors: F. Fiore, A. Bongiorno, K. Boutsia, R. Fassbender, M. Verdugo (0.0)

Clusters of galaxies are the largest gravitationally bound objects in the universe, consisting of hundreds of galaxies. Because of the deep gravitational potential well of a cluster, scientists often use it to study galaxy formation in a closed system. However, both theoretical calculations and simulations tend to predict too much cool gas and too many newborn stars. This is referred to as “the cooling flow problem”, and the best candidate for explaining this discrepancy is feedback by the central active galactic nucleus (AGN)–a bright and compact region at the center of a galaxy. Even though most of the clusters show a signature of a powerful jet in the center (kinetic-mode feedback), only a few clusters have extremely-bright AGNs in their central galaxies (quasar-mode feedback).

In this poster, I will introduce the Cluster Hiding in Plain Sight (CHiPS) survey with the aim to discover new galaxy clusters surrounding X-ray-bright point sources. The CHiPS survey is designed around the idea that the centrally concentrated galaxy clusters can be misidentified as field AGN in previous all-sky surveys. I will present our first newly discovered galaxy cluster, surrounding the quasar PKS1353-341, at z = 0.223, along with new Chandra observations of the galaxy cluster and its central AGN. We have also completed the optical follow-up of the CHiPS targets and were awarded Chandra observations of the 5 most promising candidates. We present one of these new observations, which appears to be a second newly-discovered quasar-hosting cluster. By performing a detailed study of these objects, we can investigate the impact a central quasar has on the intracluster medium and demonstrate the potential of the CHiPS survey to find massive nearby clusters with extreme central properties that may have been misidentified by previous surveys.

Co-Authors: Michael McDonald (MIT)

Based on archival Chandra observations with a total exposure of 1.3 Ms, we study X-ray point sources in the Fornax cluster of galaxies, with the primary aim of searching for intra-cluster X-ray source populations. We detect 1177 point sources out to a projected radius of ∼30 arcmin (∼180 kpc) from the cluster center and down to a limiting 0.5-8 keV luminosity of ∼3×10³⁷ erg s^-1. We construct source surface density profile, after excluding sources associated with foreground stars, known globular clusters, ultra-compact dwarfs and galactic nuclei. From this profile we statistically identify ∼183 excess sources that are not associated with the bulk stellar content of the individual member galaxies of Fornax, nor with the cosmic X-ray background. Taking into account Poisson error and cosmic variance, the cumulative significance of this excess is at ≳2σ level (with a maximum of 3.6σ) outside three effective radii of the central giant elliptical, NGC 1399. The luminosity function of the excess sources is found to be significantly steeper than that of the GC-hosting sources (presumably low-mass X-ray binaries [LMXBs]), disfavoring the possibility that unidentified GCs are primarily responsible for the excess. We show that a large fraction of the excess can be related to the extended stellar halo of NGC 1399 and/or the diffuse intra-cluster light, thus providing strong evidence for the presence of intra-cluster X-ray sources in Fornax, the second unambiguous case for a galaxy cluster after Virgo. Other possible origins of the excess, including supernova-kicked LMXBs and stripped nucleated dwarf galaxies are discussed.

Co-Authors: Meicun Hou, Zhenlin Zhu, Zhiyuan Li (Nanjing University)

Based on constraints from Big Bang nucleosynthesis and the cosmic microwave background, the baryon content of the high-redshift Universe can be precisely determined. However, at low redshift, about one-third of the baryons remain unaccounted for, which poses the long-standing missing baryon problem. The missing baryons are believed to reside in large-scale filaments in the form of the warm-hot intergalactic medium (WHIM). In this project, we employed a novel approach to explore the hot phases of the WHIM. Specifically, we utilized Chandra LETG data of the luminous quasar, H1821+643, along with previous measurements of UV absorption line systems and spectroscopic redshift measurements of galaxies toward the quasar’s sightline. We repeatedly blueshifted and stacked the X-ray spectrum of the quasar corresponding to the redshifts of 17 absorption line systems. Based on the stacked data, we detected an O VII absorption line that exhibits a Gaussian line profile and is statistically significant at the 3.3σ level. Since the redshifts of the UV absorption line systems were known a priori, this is the first definitive detection of an X-ray absorption line originating from the WHIM.

Co-Authors: Orsolya Kovacs, Randall Smith, Ralph Kraft, William Forman (SAO)

Using Chandra observations, we found that there is a huge reservoir of ionized gas around the Milky Way, with a mass of over 2 billion solar masses and a radius of over 100 kpc. The baryonic mass fraction of this gas is consistent with the Universal value. Similar to the Milky Way, other spiral galaxies should also have massive, extended reservoirs of ionized hot gas in the circumgalactic medium (CGM). Searches of such a warm-hot gas in CGMs of external galaxies, however, have given mixed results. Theoretical models suggest that CGM properties depend on galaxy properties such as gravitational mass, stellar mass and specific star formation rate (sSFR). Therefore, to understand the physics of galaxy formation and evolution and the role of accretion and feedback mechanisms, we must probe the entire parameter space of these galaxy properties. We have designed a program to observe the CGM of external galaxies with this in mind.

I will present Chandra/XMM-Newton/Suzaku observations probing the CGM of the Milky Way and other external spiral galaxies. I will discuss the comprehensive phenomenological picture of the CGM of spiral galaxies and compare that with theoretical models of galaxy formation.

Co-Authors: Smita Mathur, Sanskriti Das, Yair Krongold, Fabrizio Nicastro (0.0)

Hot, million degree gas appears to pervade the Milky Way halo, containing a large fraction of the Galactic missing baryons. This circumgalactic medium (CGM) is probed effectively in X-rays, both in absorption and in emission. The CGM also appears to be anisotropic, so we have started a program to determine CGM properties along several sightlines by combining absorption and emission measurements. I will present the emission measure close to the Chandra absorption sightlines using new Suzaku and Chandra observations. Our results show that the warm-hot gas in the CGM of the Milky Way is anisotropic. I'll review current status of this field, discuss implications of our results to models of galaxy formation and evolution, and outline paths for future progress.

Co-Authors: Anjali Gupta, Smita Mathur, Yair Krongold, Fabrizio Nicastro (0.0)

From the soft X-ray observations in past two decades, the circumgalactic medium (CGM) of the Milky Way has been known to be warm-hot at 10^6.3 K, extended, massive, and anisotropic. These studies using oxygen as the tracer element have been limited to a single temperature model of the Galactic CGM. In our deep 1.85 Ms XMM-Newton spectrum of a background blazar, we detected the z=0 NeX absorption line for the first time. A combined modeling of nitrogen, oxygen and neon lines led to the discovery of a very hot 10^7.0 K CGM phase, coexisting with the warm-hot 10^6.1 K phase. The hot phase is significantly α-enhanced, implying core-collapse supernovae enrichment. We also found that nitrogen and neon are significantly super-solar than oxygen in the warm-hot phase, indicating oxygen depletion onto the circumgalactic dust. Additionally, we analyzed the XMM-Newton emission spectrum around the same sightline. We again detected two temperatures from the CGM at 10^6.3 K and 10^6.8 K in emission. By comparing the temperatures obtained from emission with those from absorption, we find that they are not consistent with each other, unlike the previous one-temperature models. This provides us with interesting insights into the nature of emitting and absorbing systems. Taking into account emission and absorption analyses of the Galactic CGM along many sightlines in literature, we rule out the picture of a single temperature warm-hot CGM. We discuss several possibilities objectively, and conclude that most likely we are observing multiple (3 to 4) discrete temperature components between 10^5.6 K and ≥10⁷ K. Our results provide important inputs to theoretical models of thermal history, mixing and chemical enrichment of the CGM, and the co-evolution of the Galaxy and its CGM. If the multi-temperature CGM is the generic property of the Milky Way CGM, then previous single-temperature models would have underestimated the CGM mass. This has significant implications for the missing-baryons problem.

Co-Authors: Smita Mathur, Anjali Gupta, Fabrizio Nicastro, Yair Krongold (0.0)

The circumgalactic medium (CGM) is a very important component of a galaxy, regulating the inflow from the intergalactic medium, outflow from the stellar disk, and harboring the largest baryon reservoir. Precipitation from the CGM also regulates the star-formation rate in a galaxy. Characterizing the physical conditions in the CGM is thus critically important to understanding galaxy evolution, and the role of feedback. The CGM is expected to be warm-hot, observable in X-rays, but we have had only modest success in detecting and characterizing the CGM of external Milky Way-type L* galaxies, beyond the Milky Way. The CGM is best probed by intervening high-ionization metal absorption lines in the spectra of background quasars, but given the current technology, such observations are hard. The spectra often have low signal-to-noise ratio, and random searches are very expensive. We used a novel approach to solve this problem by selecting a UV sign-post for the CGM. Our Chandra LETG observations probed the CGM of a galaxy known to have -broad- OVI absorption, with no associated Ly-alpha; this is highly suggestive of the presence of the warm-hot CGM. Our preliminary analysis of our 350ks Chandra observation shows OVII absorption line at the expected wavelength (this will be confirmed by the time of the conference). This is the first discovery of the warm-hot CGM in a Milky Way-type external galaxy in absorption! This is exciting, because the combination of UV and X-ray data allows us to uniquely determine the physical conditions in the CGM and its radial extent. I will present these results and their implications for the CGM science.

Co-Authors: Anjali Gupta, Yair Krongold, Fabrizio Nicastro, Sanskriti Das (CSCC, Columbus, OH; UNAM, Mexico; INAF, Italy; OSU.)

We are carrying out a refined search in X-rays for haloes scattered by intergalactic dust. The primary obstacle in detecting faint dust-scattered halos is the presence of low level emission in the wings of the point spread function due to the point source — to overcome this obstacle, we exploit the time invariability (due to light travel time delay of scattered photons) of the halos. We use distant point sources observed at different flux levels. We have identified candidate sources, and are carrying out a detailed quantitative analysis. This technique has the potential to reveal or set a cosmologically constraining the upper bound on the density of intergalactic dust.

Co-Authors: Frits Paerels (Columbia University)

The second major release of the Chandra Source Catalog, CSC 2.0, offers significant improvements over the previous catalog release, CSC 1.1, both in the amount of data included and the analysis procedures followed. CSC 2.0 includes ∼315,000 unique compact X-ray sources and ∼1000 highly extended sources, and covers ∼550 square degrees of the sky. The sensitivity limit for compact sources has been significantly improved to ∼5 net counts on-axis. Both the additional data and the improved analysis techniques mandate a full re-characterization of the statistical properties of the catalog, namely, detection efficiency, false source rate, sensitivity, and accuracy of source properties. We present a preliminary summary of that work here. As in CSC 1.1, we use both analysis of real CSC 2.0 catalog results and extensive simulations of blank-sky and point source populations to characterize the catalog.

This work has been supported by NASA under contract NAS 8-03060 to the Smithsonian Astrophysical Observatory for operation of the Chandra X-ray Center.

Co-Authors: Ian N. Evans 1, Joseph B. Miller 1, Janet D. Evans 1, Christopher E. Allen 2, Craig S. Anderson 1, Glenn Becker 1, Jamie A. Budynkiewicz 1, Douglas Burke 1, Judy C. Chen 1, Francesca Civano 1, Raffaele D’Abrusco 1, Stephen M. Doe 2, Giuseppina Fabbiano 1, J. Rafael Martinez Galarza 1, Danny G. Gibbs II 1, Kenny J. Glotfelty 1, Dale E. Graessle 1, John D. Grier Jr. 1, Roger M. Hain 1, Diane M. Hall 3, Peter N. Harbo 1, John C. Houck 1, Jennifer L. Lauer 1, Omar Laurino 1, Nicholas P. Lee 1, Michael L. McCollough 1, Jonathan C. McDowell 1, Warren McLaughlin 1, Douglas L. Morgan 1, Amy E. Mossman 1, Dan T. Nguyen 1, Joy S. Nichols 1, Michael A. Nowak 4, Charles Paxson 1, Menelaos Perdikeas 1, David A. Plummer 1, Arnold H. Rots 2, Aneta L. Siemiginowska 1, Beth A. Sundheim 1, Sinh Thong 1, Michael S. Tibbetts 1, David W. Van Stone 1, Sherry L. Winkelman 1, and Panagoula Zografou 1 (1 Center for Astrophysics | Harvard & Smithsonian, 2 Formerly Center for Astrophysics | Harvard & Smithsonian, 3 Northrup Grumman Corporation, 4 Formerly MIT Kavli Institute)

Cross-matching the second release of the Chandra Source Catalog (CSC2.0) presents a number of unique challenges that need to be adequately addressed in order to achieve a high level of reliability and confidence in identifications that are made purely on the basis of spatial properties.

The overriding consideration is that in cross-matching across disparate parts of the spectrum, from radio to infrared to visible light to X-rays, a reliable match probability needs to be obtained, since objects may appear (or fail to appear) dramatically differently in different parts of the spectrum, because of their overall spectral properties and potential differences in obscuration. It is not sufficient to base the determination of the match probability solely on position uncertainties. One also needs to take into account the instrumental Point Spread Functions (PSF), the local density of sources, and, explicitly, the occurrence of ambiguous matches. This is especially important since Chandra's PSF varies very significantly over its field of view.

We have built a cross-match tool that is based on the Bayesian algorithms presented by Budavari, Heinis, and Szalay (ApJ 679, 301 and ApJ 705, 739), extended by allowing for elliptical errors, PSFs, local source densities, and the the explicit identification of ambiguous matches. This necessitated determining composite PSFs for CSC2.0 Master Sources, cross-matching individual CSC2.0 ensembles, proper thresholding of the match probabilities, and logic to identify ambiguities. We will present preliminary results of cross-matching CSC2.0 with SDSS and AllWISE catalogs.This work has been supported by NASA under contract NAS 8-03060 to the Smithsonian Astrophysical Observatory for operation of the Chandra X-ray Center.

Co-Authors: The Chandra Source Catalog R2.0 Collaboration (CfA/CXC)

The second release of the Chandra Source Catalog (CSC) contains all sources identified from sixteen years' worth of publicly accessible observations. The vast majority of these sources have been observed with the ACIS detector and have spectral information in 0.5-7 keV energy range. Here we present a discussion of the available spectral properties that can be found in the catalog. Sources with high signal to noise ratio (exceeding 150 net counts) were fit with three models: an absorbed power-law, blackbody, and Bremsstrahlung emission. The fitted parameter values for these three models were included in the catalog with the calculated flux for each model. The CSC also provides for all of the sources, energy fluxes computed from the normalization of predefined absorbed power-law, black-body, Bremsstrahlung, and APEC models needed to match the observed net X-ray counts. Hardness ratios were calculated for each source between pairs of energy bands (soft, medium and hard).

For sources that have been observed multiple times we performed a Bayesian Blocks analysis to identify their variability. For each of the blocks a joint fit is performed for the mentioned spectral models and the fit parameters are stored in a user data product. The spectral parameters for the most significant block (based on highest flux) will be stored in the CSC databases at the master level.In addition, we provide access to data products for each source: a file with source spectrum and the background spectrum (pha3), a file with the "effective area" as a function of energy (arf3), and the spectral response of the detector (rmf3).As a case study of how these spectral properties can be used we will examine a group of ULX sources found from Chandra datasets (Swartz,D.et al.,2011, ApJ,741,49S) and compare results from the catalog with published results.This work has been supported by NASA under contract NAS 8-03060 to the Smithsonian Astrophysical Observatory for operation of the Chandra X-ray Center.

Co-Authors: Aneta L. Siemiginowska 1, Douglas Burke 1, Ian N. Evans 1, Francis A. Primini 1, Joseph B. Miller 1, Janet D. Evans 1, Christopher E. Allen 2, Craig S. Anderson 1, Glenn Becker 1, Jamie A. Budynkiewicz 1, Judy C. Chen 1, Francesca Civano 1, Raffaele D'Abrusco 1, Stephen M. Doe 2, Giuseppina Fabbiano 1, J. Rafael Martinez Galarza 1, Danny G. Gibbs II 1, Kenny J. Glotfelty 1, Dale E. Graessle 1, John D. Grier Jr. 1, Roger M. Hain 1, Diane M. Hall 3, Peter N. Harbo 1, John C. Houck 1, Jennifer L. Lauer 1, Omar Laurino 1, Nicholas P. Lee 1, Jonathan C. McDowell 1, Warren McLaughlin 1, Douglas L. Morgan 1, Amy E. Mossman 1, Dan T. Nguyen 1, Joy S. Nichols 1, Michael A. Nowak 4, Charles Paxson 1, Menelaos Perdikeas 1, David A. Plummer 1, Arnold H. Rots 1, Beth A. Sundheim 1, Sinh Thong 1, Michael S. Tibbetts 1, David W. Van Stone 1, Sherry L. Winkelman 1, Panagoula Zografou 1, Saeqa Vrtilek 1, Dong-Woo Kim 1, and Nazma Islam 1 (1 Center for Astrophysics | Harvard & Smithsonian2 Formerly Center for Astrophysics | Harvard & Smithsonian3 Northrup Grumman Corporation4 Formerly MIT Kavli Institute)

While productivity is a key metric for the success of an observatory or archive, it is not the only one. Another gauge is scientific accessibility — which we can measure as the number of different authors, institutions, communities, or countries publishing using those data. The scientific accessibility of astronomical data is critical to maintain a rich, flourishing, and growing discourse in astronomy and promote diversity in the scientific community. So how has the accessibility of Chandra data changed over the two decades that Chandra has been in operation? Until recently, such investigations were quite labor intensive, but the new ADS API makes gathering author and affiliation information much easier. Using the Chandra Bibliography and the new ADS API, I will explore the science accessibility of Chandra data throughout the mission as it relates to Chandra proposals; PhD theses based on Chandra data; and archival versus non-archival Chandra Science Papers.

Co-Authors: Sherry Winkelman, Raffaele D'Abrusco (Center for Astrophysics | Harvard & Smithsonian, Center for Astrophysics | Harvard & Smithsonian)

The second CXO source catalog (CSC v2) contains over 300,000 X-ray sources and a vast majority of these sources have been observed serendipitously. A reliable automated classification of these sources is a challenging task. It can greatly increase the populations of objects with known astrophysical types, and reveal unusual and rare sources. Compared to XMM-Newton, the unprecedented angular resolution of CXO allows for a much more reliable optical/IR counterpart identification for X-ray sources in the Galactic plane, especially within crowded environments. We discuss the recent developments to our machine learning classification pipeline (MUWCLASS) driven by CSC v2 and recent sensitive surveys at optical/IR wavelengths. We will present the updates to the training data set and pipeline, showing how these improvements have impacted the pipeline's performance, and demonstrate applications of the pipeline to Galactic fields.

Co-Authors: Jeremy Hare, Hui Yang (NASA GSFC, The George Washington University)

We have compiled a catalog of coronal line emitting sources observed with the Chandra gratings over the past 20 years. Grating observations are typically long duration looks at bright, active stars, and are ideally suited to carry out spectrally resolved timing analysis. We carry out a full reprocessing of the data, extract the photon events, and compute light curves and fluxes in several passbands and emission lines of interest. The results of the analyses, which incorporates several statistically sophisticated algorithms, including lines detected via a Haar wavelet based method, changepoints in wavelength-time space using Automark, and flare power-law distributions via an ABC-like (Approximate Bayesian Computation) MCMC method, are presented as a web-accessible database.

Co-Authors: Jeremy Drake, Steve Saar (CfA, CfA)

JUDO2 (2nd generation of JAXA Universe Data Oriented; http://darts.isas.jaxa.jp/astro/judo2) is a web-tool to access not only JAXA's science satellite data but also other satellite and ground-based all-sky data. We adopt Aladin Lite which allows you to access public HiPS (Hierarchical Progressive Survey) format data all over the world and to browse, move, zoom in/out them.

We produce HiPS data of JAXA's projects, MAXI, Hitomi, Suzaku, ASCA (X-rays) and Akari and BICE (infrared). Also, we create HiPS images of Swift BAT and constellations (in different representations), and HiPS catalogs ofMAXI, Swift BAT and Swift XRT. These HiPS data are available at http://darts.isas.jaxa.jp/pub/judo2/HiPS/ which are accessible by Aladin Desktop or Aladin Lite. Also, we create time-series of MAXI HiPS data, so that users can display yearly, monthly, weekly and daily all sky MAXI images.

Two HiPS images can be displayed being overlaid each other, while you can control transparency of the top image. Over the images, supplemental information are drawn such as instrument field of views ("foot-prints"), constellation boundaries, and source catalogs. The displayed foot-prints are linked to each pointing information, where direct links to the archival data are available. Currently foot-prints of the following satellitesare available; Hitomi, Suzaku, ASCA, Akari, XMM, Chandra, NuSTAR and NICER.Observation information of XMM, Chandra (depending on observation mode), NuSTAR and NICER are daily updated.In this manner, users can get to know, at a glance, which parts of the sky are observed by which satellites, and graphically choose particular archival data.

In addition, JUDO2 has direct link to DARTS's UDON2 (2nd generation of Universe via DARTS ON-line) and MAXI on-demand analysis system (http://maxi.riken.jp/mxondem/), with which users can quickly look at light-curves and spectra of particular sources or region of the sky. With MAXI on-demand system, fully calibrated spectral files and spectral responses are also available.

The AtomDB project collects a large database of Atomic Data and produces a range of models for emission in plasmas. These include thermal plasmas (the apec model), non-equilbirum models (rnei), which have been part of XSPEC for many years. Recently, we have extended our available models:

• Our charge exchange model (ACX) has been updated to ACX2, which is based on the CX cross section data from the Kronos project (Mullen+2016, 2017, Cumbee+2018)
• We have added a model for electron-electron bremsstrahlung emission, based on the work of Nozawa+(2009). This is relevant for modeling high temperature plasmas (T>10⁸K)
• We have added a model of non-Maxwellian (Kappa) distributed electrons based on Hahn & Savin (2015)

We demonstrate these models being used for a range of different plasmas, based on the work of Cui+(2019)

In addition, we have enhanced PyAtomDB and the AtomDB website to now allow much greater access to the underlying atomic database. This includes replicating many of the features of the popular AtomDB app in our website. We show the new online access and spectral analysis tools available.

Co-Authors: Xiaohong Cui, Marcus Dupont, Randall Smith, Nancy Brickhouse (National Astronomical Observatory - Chinese Academy of Science, New York University, Smithsonian Astrophysical Observatory,Smithsonian Astrophysical Observatory)

The particle background caused by high energy particles in orbit has a significant contribution to X-ray observations, especially for diffuse and faint sources such as supernova remnants, pulsar wind nebulae and clusters of galaxies. The spectrum of the Advanced CCD Imaging Spectrometer (ACIS) particle background is composed of continuum components and fluorescence emission lines produced in the materials surrounding the detectors. Precise estimation of the particle background spectrum for each observation and detector region of interest is essential for studies of extended objects. In order to investigate the time and spatial variations of the ACIS particle background, we used data obtained from 2002 to 2016 with the detector in the stowed position so that only source of events was due to the particle background. The data were taken with ACIS-I0, I2, I3, S1, S2 and S3 in very faint and faint mode. The data showed ∼+/-50% variation of the fluxes according to the solar activity. We constructed a template spectral model which explains the average spectrum. The model included continuum components, line emission of Al, Ni and Au, and the broad line emission produced by the inappropriate correction of charge transfer inefficiency for events that convert in the frame store region of the CCDs. We confirmed that the spectra extracted from the entire CCD did not show significant variations of the shape with time. We did find significant spatial variations of the spectra in each chip which we were able to model by allowing the energies of frame store lines to vary. We modeled these time and spatial variations to provide the proper particle background spectrum for an arbitrary observation and region of interest. Finally, we confirmed the validity of our modeling using the blank-sky observations.

Co-Authors: Paul P. Plucinsky, Terry Gaetz, Aya Bamba (Harvard-Smithsonian Center for Astrophysics, Harvard-Smithsonian Center for Astrophysics, The University of Tokyo)

The gain of Chandra's HRC-S detector has decreased significantly over the past 20 years, by around a factor of four in some areas. Although the HRC-S has very little energy resolution (median pulse height changes by less than 10% for a factor of two change in X-ray energy), it has enough that an accurate gain calibration allows around half of the background signal (after standard Level-2 pipeline processing) to be filtered out with only about 1% loss of valid X-ray events.

We describe our analysis of nearly 100 LETG/HRC-S observations of bright sources (HZ 43 for long wavelengths, Mkn 421 and PKS 2155 for short, and three novae for intermediate wavelengths) to measure the temporal and spatial dependence of the HRC-S gain on scales of ∼80 pixels along the LETG dispersion axis (about 0.6 Å). We include corrections for the effects of spectral contamination by higher-order diffraction, and also utilize 30 short grating-less observations of HZ43 to map gain in areas where gain losses are especially large and/or grating spectra are faint.

Co-Authors: Peter W. Ratzlaff (SAO/CXC)

We have invented a new type of X-ray interferometers, MIXIM, which simply consists of a grating (multiple slits) and a pixel detector. This configuration provides X-ray images as multiple slit camera can do. If we employ a grating of a pitch d of 5micrometer, and opening fraction f of 0.2, separated from the detector by the distance z of 50cm, we expect the image width of 0.4’’. It suggests that Chandra resolution is possible with very small satellites. Diffraction hampers this simple idea in gneral. However, by selecting X-ray events of which X-ray energy satisfies the Talbot interference condition, we expect a sharp image of the X-ray light source convolved with the multiple slits(Hayashida+2016).

We irradiated parallel X-ray beam to our MIXIM system in a synchrotron facility and succeeded in obtaining the image of the source of which image width of sub-arcsecond (Hayashida+2018). In the latest experiments. we confirmed the energy band width of the MIXIM is about 10%, reasobale for continuum sources. Our current record for the image width is 0.09'' with z of 867cm and 0.55’’ with z of 46 cm. We recently succeeded in 2 dimensional images by stacking two gratings diagonally.

In addition to its simple configuration and superior resolution, another advantage of MIXIM is in its scalability. If we tune z and d accordingly, MIXIM with z of 10 m (e.g.parasites to typical X-ray observatory) can go 0.1’’. That with z of 100 m (e.g. formation flights) can go 0.01’’ resolution, comparable to ALMA. Ultimate goal would be z of millions km as for LISA gravitation wave observatory. In this case, micro-arcsecond X-ray images are expected, i.e., X-ray color image of black hole event horizon. Future prospects will be discussed with limitation and technical barrier of this methods in space.

AXIS is a probe-class concept that was recently submitted to the 2020 Decadal survey. AXIS will extend the legacy of Chandra-ACIS and enhance the science of high angular resolution X-ray imaging in the next decade with 0.3 arcsecond angular resolution over a 7 arcmin radius field of view and an order of magnitude more collecting area than Chandra in the 0.3-12 keV band with a cost consistent with a probe. In this talk, I will present some of the science enabled by high-resolution X-ray imaging, including: the growth and fueling of supermassive black holes, fast follow-up of the transient, multimessenger universe, galaxy formation and evolution and the microphysics of cosmic plasmas. With a nominal launch date of 2028, AXIS will be an important successor to Chandra-ACIS and a technology demonstration of the optics for future flagships like the proposed Lynx Observatory.

Co-Authors: Richard Mushotzky (PI) and the AXIS Team (0.0)

HERMES-TP/SP is a constellation of six 3U nano-satellites hosting simple but innovative X-ray detectors for the monitoring of Cosmic High Energy transients such as Gamma Ray Bursts and the electromagnetic counterparts of Gravitational Wave Events, and for the determination of their position. The projects are funded by the Italian Space Agency and by the European Union’s Horizon 2020 Research and Innovation Programme under Grant Agreement No. 821896. HERMES-TP/SP is an in orbit demonstration, that should be tested in orbit by the beginning of 2022. It is intrinsically a modular experiment that can be naturally expanded to provide a global, sensitive all sky monitor for high energy transients. On behalf of the HERMES-TP and HERMES-SP collaborations I will present the main scientific goals of HERMES-TP/SP, as well as a progress report on the payload, service module and ground segment developments.

The X-ray Imaging and Spectroscopy Mission (XRISM), developed under a JAXA-NASA international collaboration with ESA's participation, will enable non-dispersive high-resolution spectroscopy with an X-ray microcalorimeter array, and will recover the science lost by the short-lived Astro-H/Hitomi mission. XRISM will reveal the formation and evolution of the Universe by accurately measuring the gas dynamics, energetics, and chemical composition of the intracluster medium. Details of other extended or compact objects (e.g., supernova remnants, active galactic nuclei) will also be investigated with an unprecedented spectral resolution. XRISM also has an important role as a 'path-finder' for other future high-resolution spectroscopy missions, such as Athena, Arcus, and Lynx. This talk will summarize the current status of the development and our plan for the science operations, particularly during the performance verification (PV) phase. We will also explain the concept of "XRISM Guest Scientist (XGS) Program", opening to the whole astronomical community an opportunity to participate in scientific exploitation of the PV-phase observations.

Co-Authors: XRISM Collaboration (0.0)

Arcus provides high-resolution soft X-ray spectroscopy in the 12-50 Å bandpass with unprecedented sensitivity, including spectral resolution >2500 and effective area > 250 cm$^2$. The three top science goals for Arcus are (1) to measure the effects of structure formation imprinted upon the hot baryons that are predicted to lie in extended halos around galaxies, (2) to trace the propagation of outflowing mass, energy, and momentum from the vicinity of the black hole to extragalactic scales as a measure of their feedback, and (3) to explore how stars form and evolve. Arcus uses the same 12 m focal length grazing-incidence Silicon Pore X-ray Optics (SPOs) that ESA has developed for the Athena mission; the focal length is achieved on orbit via an extendable optical bench. The focused X-rays from these optics are diffracted by high-efficiency Critical-Angle Transmission (CAT) gratings developed by the same group that built the Chandra HETG gratings. The resulting dispersed photons are imaged with flight-proven CCD detectors and electronics. Combined with the high-heritage NGIS LEOStar-2 spacecraft and launched into 4:1 lunar resonant orbit, Arcus provides high sensitivity and high efficiency observing of a wide range of astrophysical sources.

XL-Calibur is a second-generation balloon-borne hard X-ray polarimety mission. It builds on the success of X-Calibur, which flew from McMurdo, Antarctica on a 2.5 day flight from Dec. 29, 2018 to Jan. 1, 2019 and placed limits on the polarization properties of the accreting pulsar GX 301-2 in the 20-50 keV range.

XL-Calibur will have greatly improved sensitivity thanks to several upgrades. It will use the FFAST mirror, which has a larger effective area. The CZT detectors will be thinner, which reduces background while staying nearly as efficient. The last major improvement is to the anti-coincidence shielding, where we will shorten the anti-coincidence timing window, lower the active shield threshold, and add passive polyethylene shielding.

We plan on flying this upgraded instrument on two flights from Kurina, Sweden (in 2021 and 2022), and one from McMurdo (in 2024). During these three flights, XL-Calibur will be able to observe a variety of sources, such as the accreting pulsars GX 301-2 and Her X-1, the accreting stellar mass black hole Cyg X-1, the Crab nebula, and further sources to be chosen based on flux levels at the time of flight.

Co-Authors: Awaki Hisamitsu,Bose Richard,Braun Dana,de Geronimo Gianluigi,Dowkontt Paul,Enoto Teruaki,Errando Manel,Fukazawa Yasushi,Gadson Thomas,Guarino Victor,Gunji Shuichi,Hayashida Kiyoshi,Heatwole Scott,Ishida Manabu,Iyer Nirmal Kumar,Kislat Fabian,Kiss Mózsi ,Kitaguchi Takao ,Krawczynski Henric,Kushwah Rakhee ,Lanzi James,Li Shaorui,Lisalda Lindsey ,Maeda Yoshitomo,Matsumoto Hironori,Miyazawa Takuya,Mizuno Tsunefumi,Okajima Takashi,Pearce Mark,Peterson Zachary,Rauch Brian,Ryde Felix,Saito Yoshitaka,Stana Theodor-Adrian,Stuchlik David,Takahashi Hiromitsu,Takeda Tomoshi,Tamagawa Toru,Tamura Keisuke,Tsunemi Hiroshi,Uchida Nagomi,Uchiyama Keisuke,West Andrew,Yoshida Yuto (Ehime University,WUSTL,WUSTL,Stony Brook, DG Circuits,WUSTL,Kyoto University,WUSTL,Hiroshima University,Wallops Flight Facility,Guarino Engineering,Yamagata University,Osaka University,Wallops Flight Facility,ISAS,KTH, OKC,UNH,KTH, OKC,RIKEN,WUSTL, MCSS, & CQSs,KTH, OKC,Wallops Flight Facility,BNL,WUSTL,ISAS,Osaka University,OIST,Hiroshima University,GSFC,KTH, OKC,Wallops Flight Facility,WUSTL,KTH, OKC,ISAS,KTH, OKC,Wallops Flight Facility,Hiroshima University,Tokyo University of Science,RIKEN,Nagoya University,Osaka University,Hiroshima University,Tokyo University of Science,WUSTL,Tokyo University of Science)

Many of the accretion disks of stellar mass black holes in X-ray binaries and supermassive black holes at the centers of Active Galactic Nuclei (AGN) are likely misaligned with the angular momentum of the distant accretion disk material. In such systems, the interplay of disk viscosity and general relativistic frame dragging is expected to cause the disk to warp or break into two or more distinct planes – this is called the Bardeen-Petterson effect. Recent general relativistic magnetohydrodynamic (GRMHD) simulations have found that this Bardeen-Petterson configuration is indeed possible, with the warp possibly occurring relatively close to the black hole. We discuss here the scientific prospects of stellar mass black hole and AGN observations with NASA's upcoming Imaging X-ray Polarimetry Explorer (IXPE), based on our general relativistic ray tracing simulations of black holes with Bardeen-Petterson-type accretion disk configurations. We emphasize the importance to compliment the IXPE observations with spectro-temporal observations gathered with other satellites such as the X-ray telescope on the Neil Gehrels Swift Observatory and the Nuclear Spectroscopic Telescope Array (NuSTAR).

Co-Authors: Henric Krawczynski (Washington University in St. Louis)