Abstracts of Talks
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I’ll share new results from our CATS Chandra survey which utilizes more than 25 Ms of Chandra data and identifies ∼40,000 X-ray AGN. The aim is to trace the evolution of AGN in dense environments from early-times, through the peaks of AGN and SF activity, to the present day and to probe the role of environment in triggering and quenching AGN activity.
Thanks to the exquisite spatial resolution of Chandra, we discovered relativistic jets in X-rays in XTE J1550-564 and H1743-322. In this talk, we will present new detections of X-ray jets in additional sources (GX 339-4, MAXI J1820+070 and possibly others ), describe the jets' deceleration and morphology evolution, and highlight the extreme particle re-acceleration that occurs when the relativistic jets interact with the interstellar medium. Based on the observed behavior, such phenomena appear more common than previously thought and we will discuss the overall implications.
Why the interaction between Jupiter’s atmosphere and magnetosphere should pulse in this manner, and how planets intermittently inject such energetic ions into their poles has remained unknown. Over the past three years, the arrival of NASA’s Juno spacecraft at Jupiter has allowed Chandra and XMM-Newton to usher in an entirely new revolution in our understanding of the highest energy emissions from planets. Several extensive campaigns were scheduled to coincide with the paradigm-shifting in-situ and multi-waveband measurements being conducted by NASA’s Juno spacecraft. Here, we share some of the highlights from these joint Juno-Chandra campaigns so far. We will introduce a truly multi-waveband image of Jupiter by connecting synchronised Hubble UV, Juno Radio and Chandra X-ray emissions. We will also show evidence of strong correlations between in-situ measurements of pulsed processes in Jupiter’s magnetosphere and simultaneous Chandra and XMM-Newton observations of Jovian X-ray pulsations with the same time intervals. We observe that as the magnetospheric processes change pulsation rate so do the X-ray aurorae, suggesting that these magnetospheric processes are what drive X-ray aurorae at planets.
We present the results of a set of X-ray stacking studies of star-forming galaxies at different redshifts, whose goal is to test of the connection between the redshift evolution and Z-dependence of HMXBs. We use samples of galaxies at z∼0.3, z∼0.7, and z∼2 with Z measurements from the hCOSMOS, zCOSMOS, and MOSDEF surveys, respectively. Stacking Chandra data from the deep extragalactic fields in which these galaxies reside, we confirm that the LX/SFR of galaxies overall increases with redshift. Splitting our samples into different Z bins, we find that at each redshift, LX/SFR decreases with Z, and that, at a given Z, the LX/SFR of HMXB-dominated galaxies is consistent from z=0 to z=2. The LX-SFR-Z relation we measure is in good agreement with some theoretical predictions and with the LX-SFR-Z relation in the local Universe. Thus, these studies provide the first direct evidence that the redshift evolution of the LX/SFR of HMXBs is indeed driven by metallicity.
Since ACIS suffers a loss of effective area due to the contamination and the HRC-S has a high level of noise, we performed the observations with HETG/HRC-I. This is the first time that we resolve spectral lines in a science observation with HETG/HRC-I, which offers the spectral resolving power of the HETG with the soft sensitivity of the HRC. Given that the contamination on ACIS still increases, this instrumental combination can help Chandra observers in all fields who require high-resolution grating data at soft energies for the remainder of Chandra's lifetime.
We studied this short-wavelength region because it is least affected by wind absorption (which we treated approximately as a foreground absorbing screen), the emission lines here are well separated, and because both emission line fluxes and the continuum shape provide significant model leverage on the highest temperature plasma model. This deep exposure conclusively shows that emission lines from high temperature H-like ions of S XVI, Ar XVIII, and Ca XX (25-50 MK) are absent. The slope of the emission measure powerlaw is consistent with clump bow-shock models and hydrodynamical simulations.
Variability, while present, was at a low enough level to justify modeling of the mean spectrum. We also determined elemental abundances of Mg, Si, S, and Ar, and found Mg and Si to be 10-20% sub-solar for this plasma model.
Acknowledgement: Support for for this work was provided by NASA through the Smithsonian Astrophysical Observatory (SAO) Grant GO8-19011C to MIT, and by contract SV3-73016 to MIT for Support of the Chandra X-Ray Center (CXC) and Science Instruments. CXC is operated by SAO for and on behalf of NASA under contract NAS8-03060.
The first high-quality, high-resolution X-ray spectrum of any AGN was obtained by Chandra's LETGS on December 11, 1999. Contrary to expectations, the spectrum of NGC 5548 showed a series of strong, narrow, blue-shifted absorption lines, with weak or absent absorption edges. This was the first proof for a highly photo-ionized wind from this AGN. In addition, the first traces of emission lines from photo-ionized gas were found.
When Chandra revisited the source for a full week in 2002, with LETGS and HETGS observations, the spectra revealed that the wind contained multiple ionization components that were not in pressure equilibrium. In addition, clear signatures of broad emission lines were discovered. Several short duration bursts or quasi-periodic oscillations occurred with a typical duration of several hours, likely due to a rotating spot on the disk.
Follow-up observations with LETGS in 2005 and 2007 showed the source in a very low continuum flux state, allowing us to study in detail the X-ray narrow line region and assess its distance. A side-effect of the low flux in these two observations was that it was harder to study the wind in detail. This made us hesitate to re-propose this target.
However, in 2013 we conducted a multi-wavelength spectroscopic campaign on NGC 5548 with simultaneous XMM-Newton, HST, INTEGRAL, Swift and NuSTAR observations. To our surprise, the soft X-ray flux of the source was even lower than in 2007, but with a completely different spectral shape. The "normal" hard X-ray flux, the spectral shape at soft X-rays, the presence of narrow emission lines and the simultaneous UV absorption lines all pointed out that the source suffered from obscuration by a new component never seen before in NGC 5548: cold, lowly ionized, high-column density and partially covering material, just outside the broad-line region, well inside the regime of the normal ionized wind.
ToO observations with the LETGS taken the same year, when the source was in a bright state, demonstrated that the normal wind was strongly de-ionized.
The lessons learned from these key X-ray observations were fundamental in understanding the complex behavior of the broad UV lines during an intensive HST campaign conducted half a year later, again with supporting LETGS observations.
Finally, the latest spectra of NGC 5548 taken this year with HETGS show that the source is now already obscured for almost a decade. Because of somewhat less obscuration, this spectrum shows clear lines from multiple Mg and Si ions. We conclude with prospects for future missions to observe this proto-type of active galactic nucleus.
Ejection of high-speed X-ray emitting clumps from a binary has never been seen before and would not be discovered without Chandra. The study of this exciting phenomenon provides a unique insight into the properties of the pulsar and stellar winds and their interaction.