Chandra's First Decade of Discovery

Accretion and Outflows

Suzaku Observations of H 1743-322: Implications for Disk Winds

Jennifer Blum, Astronomy Department: University of Michigan
J.L.Blum (University of Michigan), J.M.Miller (University of Michigan), E. Cackett (University of Michigan), K. Yamaoka (Aoyama Gakuin University), H. Takahashi (Hiroshima University), J. Raymond (Harvard-Smithsonian Center for Astrophysics), C.S. Reynolds (University of Maryland), A.C. Fabian (Cambridge University)

Disk winds can be key to understanding disk physics and inflow-outflow connections in accreting black holes.  We observed the black hole candidate H 1743-322 in the low/hard state during the 2008 outburst with Suzaku.  The spectra rule-out Fe XXV and Fe XXVI absorption lines, and thus rule-out an ionized disk wind like that previously detected in a disk-dominated high/soft state with Chandra. Our results suggest that the wind is quenched, rather than merely too highly ionized to be detected.  This adds to a growing picture that winds and jets are anti-correlated and state-dependent.  We will report and discuss our Suzaku results in the context of inflow-outflow connections in accreting systems.

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A search for spectral features in photospheric radius-expansion X-ray bursts with Chandra

Duncan Galloway, Monash University
Herman Marshall (MIT), Yangsen Yao (U. Colorado), Nevin Weinberg (Berkeley), Zdenka Misanovic (Monash)

Spectral features arising from the surface of neutron stars are a high priority for observers, since they allow measurement of the gravitational redshift, in turn providing clues as to the neutron star equation of state. Such searches have a long history, but are yet to provide robust, reproducible results. I describe a search for such features in the spectra of an infrequent type of thermonuclear burst, that is sufficiently intense to exceed the Eddington flux at the surface and eject the outer layers of the photosphere. Recent theoretical work has suggested that such “photospheric radius-expansion” bursts may drive outflows containing ashes from previous bursts, and imprint photoionisation edges on the observed spectrum. We present analysis of the six radius-expansion bursts observed so far by Chandra, which offer as yet no evidence of discrete lines or edges. However, the accumulated signal from the peak of these six bursts is not yet sufficient to give sensitivity at the theoretically-predicted level. An observational program with Chandra triggered by observations with the Rossi X-ray Timing Explorer is currently active and aims to add substantially to the accumulated signal.

Superorbital variation in LMC X-4: tracing the precessing disk

Li-Wei Hung, Smithsonian Astrophysical Observatory
Ryan C. Hickox (SAO/Durham), Bram Boroson (SAO), Saku Vritlek (SAO)

We present Suzaku and XMM observations of the high-mass X-ray pulsar LMC X-4 at different phases in its superorbital cycle, which is due to the precession of a warped accretion disk. The superorbital period and phase for each observation is determined accurately using RXTE ASM data. At all superorbital phases, the broadband X-ray spectra are described by a high-energy power-law continuum as well as a soft blackbody component, which most likely originates from reprocessing of the hard X-rays by the inner accretion disk. As with the similar systems SMC X-1 and Her X-1, LMC X-4 shows variations in the phases of the hard and soft pulse profiles, consistent with viewing the illuminated accretion disk at different orientations.

A Further Drop into Quiescence by the Eclipsing Neutron Star 4U 2129+47

Jinrong Lin, MIT
Michael A. Nowak (MIT) and Deepto Chakrabarty (MIT)

A Further Drop into Quiescence by the Eclipsing Neutron Star 4U 2129+47 The low mass X-ray binary 4U 2129+47 was discovered during a previous X-ray outburst phase and was classified as an accretion disk corona source due to its broad and partial X-ray eclipses occurring periodically on a 5.24 hr orbit. The source entered a X-ray quiescent state in 1983 wherein its optical modulation disappeared and an F8 IV star-- rather than an expected late K or M star-- was revealed. This suggested that 4U 2129+47 might be in a hierarchical triple system. A 1% delay between two mid-eclipse epochs measured ~22 days apart was reported from two XMM-Newton observations taken in 2005, providing further support in favor of the triple nature of 4U 2129+47. Compared to a year 2000 Chandra observation, the XMM-Newton observations lacked sinusoidal orbital modulation in the light curve, and only upper limits (roughly consistent with the detection in the Chandra observation) could be placed on the presence of a powerlaw hard tail. In this work we present timing and spectral analysis of three recent XMM-Newton observations of 4U 2129+47, carried out between November 2007 and January 2008. We found that absent the two 2005 XMM-Newton observations, all other observations are consistent with a linear ephemeris with a constant period of 18857.63 s; however, we confirm the time delay reported for the two 2005 XMM-Newton observations. These new observations also confirm the disappearance of the sinusoidal modulation of the lightcurve. We further show that compared to the year 2000 it Chandra observations, all of the XMM-Newton observations have 40% lower 0.5 - 2 keV fluxes, and the most recent XMM-Newton observations have a combined 2-6 keV flux that is nearly 80% lower. Taken as a whole, the timing results support the hypothesis that the system is in a hierarchical triple system (with a third body period of at least 175 days). The spectral results raise the question of whether the drop in soft X-ray flux is solely attributable to the loss of the hard X-ray tail (which is likely related to the loss of sinusoidal orbital modulation), or is indicative of further cooling of the quiescent neutron star after cessation of residual, low-level accretion.

Radiative Models of Sgr A* from GRMHD Simulations

Monika Moscibrodzka, University of Illinois
C. Gammie (UIUC), J. Dolence (UIUC), H. Shiokawa (UIUC), P. Leung (UIUC)

Using flow models based on axisymmetric general relativistic magnetohydrodynamics (GRMHD) simulations, we construct radiative models for Sgr A*. Spectral energy distributions that include the effects of thermal synchrotron emission and absorption, and Compton scattering, are calculated using a Monte Carlo scheme for Relativistic Radiative Transport. The key model parameters are the dimensionless black hole spin a, the inclination i, and the ion-to-electron temperature ratio. The main goal of this work is to explore how model parameters are constrained by the broadband observational data (submm - X-rays).

A New Window into the Geometry of the Central Engine in AGN with High-Resolution Spectroscopy

Kendrah Murphy, MIT Kavli Institute for Astrophysics and Space Research
Tahir Yaqoob (Johns Hopkins University/GSFC)

New theoretical model results for Compton-thick reprocessors show that the effects of geometry on the X-ray spectra of AGN are large enough that constraints from real data are possible. Signatures of absorption and Compton scattering of high-energy photons in circumnuclear material, which are critically dependent on the geometry and structure of the reprocessor, are evident in the X-ray spectra of a variety of AGN. However, in order to derive robust constraints from the data, one must model the reflection continuum and line emission self-consistently. The results from our model now allow us to extract such information from high-resolution X-ray data. We show that the X-ray reflection continuum, in addition to being highly sensitive to the column density of the reprocessor and to inclination angle effects, has a dramatic dependence on the geometry of the reprocessor that has hitherto been unexploited. We highlight, in particular, the observable differences between a reflection continuum arising from a toroidal geometry and that resulting from a disk. The equivalent width of the Fe K line core, as well as the detailed shape and relative magnitude of its Compton shoulder, prove to be additional, important diagnostics of the geometry, column density, and inclination of the structure. The velocity width of the Fe K line core has the potential to reveal the spatial location of the reprocessor. However, we emphasize that the velocity width can only be accurately measured if the continuum emission and the Compton shoulder are accounted for with an appropriate model that accommodates a range of geometrical configurations. We demonstrate that new information may be deduced from current data with the application of our Compton-thick reprocessor model. We discuss further insights into AGN systems that will be made possible through measurement and modeling of relevant spectral features with future high-resolution, high-throughput spectroscopic instruments.

Dynamic Exploration of Cygnus X-3 HETG Spectra

Herbert Pablo, Center for Astrophysics, Iowa State University
Michael McCollough Center for Astrophysics

Cygnus X-3 is a very bright and unusual X-ray source. It is a high mass x-ray binary that has been studied for over 40 years. However, it wasn't until the birth of Chandra that we could take full advantage of the information provided by this unique object. In 2006, HETG/ACIS observations of Cygnus X-3 were taken during a high state. Where as some sources struggle to get hundreds of counts, in the first order of these grating observations there were over 7 million events. The richness of this spectrum allows us to try things that have not generally been done with x-ray spectra. Specifically, we have created several dynamic spectra allowing us to explore line variations in both phase and time. These dynamic spectra show that some of these lines vary both in strength and wavelength as a function of phase. We also explore the applicability of doppler tomography to Cygnus X-3. While we are only dealing with resolution around 100 km/s, this allows us to examine different emission regions within the strong wind associated with this system. Initial results are previewed and the potential knowledge that can be gleaned from this technique will be discussed.

Variable Energy Injection by a Near-Relativistic Outflow in APM 08279+5255.

Cristian Saez, Penn State University
G. Chartas, C. Saez, W. N. Brandt, M. Giustini, and G. P. Garmire.

We present results from multi-epoch spectral analysis of XMM-Newton and Chandra observations of the broad absorption line (BAL) quasar APM 08279+5255. Our analysis shows significant X-ray BALs in all epochs with rest- frame energies lying in the range of ~6.7-17 keV. The X-ray BALs and 0.2-10 keV continuum show significant variability on timescales as short as 3.3 days (proper time) confirming the intrinsic nature of the absorbing outflow and implying a source size-scale of ~10 rg, where, rg is the gravitational radius. The fitted width of the X-ray absorption troughs imply a large gradient in the outflow velocity of the X-ray absorbers with projected outflow velocities of up to 0.76c. The detected projected maximum outflow velocity of v ~ 0.76c constrains the angle between the wind velocity and our line of sight to <22 deg. Such a small angle is consistent with the unification scheme of BAL and non-BAL quasars that posits that BAL quasars are viewed almost along the outflow direction. We found a possible trend between the X-ray photon index and the maximum outflow velocity of the ionized X-ray absorber in the sense that flatter X- ray spectra appear to result in lower outflow velocities. We provide a plausible explanation for this effect. Our results on APM 08279+5255 imply that quasar winds are massive and energetic enough to influence significantly the formation of the host galaxy, provide significant metal enrichment to the ISM and IGM, and are a viable mechanism for feedback at redshifts near the peak in the number density of galaxy mergers.

Accretion Disk Dynamics in X-Ray Binaries

Norbert S. Schulz, MIT Kavli Institute for Astrophysics and Space Research
Li Ji, M. Nowak, C. R. Canizares ( all MIT), T. Kallman (GSFC)

The last decade of X-ray observations was an era of true discovery in the study of accretion phenomena in X-ray binaries. With the launch of high resolution X-ray spectrometers on board the Chandra X-ray Observatory and XMM Newton we gained novel insights in feedback processes in accretion disks. At the forefront are dynamics in winds and outflows. Recent observations now also not only reveal properties of accretion disk coronal phenomena but point us to highly variable activity in their appearance. Amongst others these include heating along the spectral branches in the Z-source Cyg X-2, short and longterm variations in the photo-ionized emissions in Cir X-1, highly variable and dynamic Ne edges in the ultra-compact binary 4U 0614+091. This presentation summarizes these recent developments and provides an outlook towards more dynamical accretion disk coronal models and perspectives for future missions.

Probing the accretion disk structure and dust distribution along the LOS of the “Big Dipper” 4U 1624-490

Jingen Xiang, Harvard College Observatory
Julia C. Lee (HCO), Michael A. Nowak (MIT), Jöorn Wilms (University of Erlangen-Nuremberg, Germany), Norbert S. Schulz (MIT)

High-resolution spectra of low mass X-ray dipping sources would reveal the strong absorption line structures, which could be used for a better understanding of the accretion disk structure. Here, we present a detailed spectral study and X-ray dust scattering halo results of the “Big Dipper” 4U 1624-490, based on our Chandra HETGS observation over the 76 ks binary orbit. While the data indicate a possible quasi-sinusoidal modulation with period of ~43 ks that might be due to changes in local obscuration, the first observed evolution of the iron absorption lines during persistent phase indicates a two-temperature plasma for their origin: a highly ionized component (T~3.0 x 10^6 K) associated with an extended accretion disk corona of radius R~3 x 1010 cm and a less ionized more variable component (T~1.0 x 106 K) coincident with the accretion disk rim. We also estimate a geometric distance to the source to be ~15 kpc, based on the analysis of halo light curve. Through the analysis of halo radial profiles, we also determine the location, uniformity, and density of ISM dust grains. Our studies of the 4U 1624-490 X-ray halo suggest that a large fraction of the column is local to the X-ray binary. Based on these studies, a viewing geometry that is mapped to changes in plasma conditions over the 4U 1624-490 orbital period is constructed.

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