Chandra's First Decade of Discovery

Session 14: Accretion, Winds and Outflows

X-ray Spectroscopic Studies of Outflows: A Chandra High Resolution Legacy

Julia Lee, Harvard University

High spectral resolution X-ray studies, particularly those with Chandra have resulted in rich discoveries of highly ionized outflows in many astrophysical systems, Galactic and extragalactic. I will review the 10 year culmination of these studies, with particular attention paid to those studies of accretion systems which have enhanced and transformed our understanding.

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Accretion states of ultraluminous X-ray sources

Roberto Soria, University College London
Doug Swartz (NASA/MSFC) et al.

Ultraluminous X-ray sources (ULXs) have extended our knowledge of accretion onto black holes, and in particular of their different “states” as a function of accretion rate. At moderate luminosities (~ 1E39-1E40 erg/s), the X-ray spectra of most ULXs are either fitted by non-standard accretion disks (eg, slim disks) or by a power-law, consistent with inverse-Compton emission (probably an extension of the “steep-power-law” state of Galactic black holes). At the highest luminosities (>~ 1E40 erg/s), most ULXs have a power-law dominated spectrum; in particular, about half of them have hard photon indices (high/hard state, Gamma <~ 1.7). In addition, two more elements are often found: a thermal “soft excess” is the signature of the standard thin disk at large radii, which constrains the radial size of the inner Comptonizing/outflow region; and a break or downturn of the power-law at ~ 5 keV provides a characteristic temperature of the electrons in the inner region. Thus, the physics of super-Eddington accretion states correlates with that of the low states, with different systems dominated either by energy advection, or mechanical output, or Comptonizing coronae. Another intriguing issue we will discuss is whether there is a cutoff in the luminosity distribution at ~ a few E40 erg/s, which would still be consistent with stellar black holes formed from direct collapse in metal-poor environments (maximum mass ~ 70 Msun). If the power-law distribution extends to higher luminosities, it requires more massive black holes, perhaps formed from mergers in dense stellar/protostellar cluster environments

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Spectroscopy of the photoionized wind and absorption dips in the Cyg X-1 system

Manfred Hanke, University of Erlangen-Nuremberg
Jörn Wilms (University of Erlangen-Nuremberg), Michael A. Nowak (MKI-CXC), Katja Pottschmidt (NASA-GSFC), Norbert S. Schulz (MKI-CXC), Julia C. Lee (SAO)

We present results from our simultaneous observations of the high-mass X-ray binary system Cygnus X-1 / HDE 226868 with Chandra-HETGS, XMM-Newton, Suzaku, RXTE, INTEGRAL, and Swift in 2008 April. The observations have been performed shortly after phase 0 of the 5.6 d orbit when our line of sight to the accreting black hole passes through the densest part of the wind of the donor star.In the context of a consistent description for the 0.5-600 keV spectrum, the high resolution gratings spectra allow us to study the composition and dynamics of the highly photoionized wind. Dense structures in this clumpy O-star wind lead to transient absorption dips in the soft X-ray band. A color-color diagram shows evidence that the additional absorber causing the dips only covers part of the X-ray emitting region. The spectroscopic analysis reveals changes in the ionization state of the wind material between dip and non-dip phases.

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Modeling X-ray binary populations in elliptical galaxies.

Tassos Fragos, Northwestern University
Kalogera, V. (Northwestern University), Fabbiano, G. (Harvard-Smithsonian Center for Astrophysics)

X-ray binaries are unique astrophysical laboratories as they carry information about many complex physical processes such as star formation, compact object formation, and evolution of interacting binary systems. Motivated by deep Chandra observations of extra-galactic populations of X-ray binaries, I will present theoretical models for the formation and evolution of populations of low-mass X-ray binaries (LMXBs) in the two elliptical galaxies NGC 3379 and NGC 4278. The models are calculated with the recently updated StarTrack code, assuming only a primordial galactic field LMXB population. StarTrack is an advanced population synthesis code that has been tested and calibrated using detailed binary star calculations and incorporates all the important physical processes of binary evolution. The simulations are targeted to modeling and understanding the origin of the X-ray luminosity functions (XLFs) of point sources in these galaxies. For the first time we explore the population XLF in luminosities below 10E37 erg/s, as probed by the most recent observational results. Furthermore, I will present a physically motivated and self-consistent prescription for the modeling of transient neutron star LMXB properties, such as duty cycle, outburst duration and recurrence time, and compare the model transient LMXB population to the Chandra X-ray survey of the two ellipticals, which revealed several transient sources. Finally, I will briefly talk about an ongoing project towards developing a new advanced computational tool for the study of X-ray binary populations formed in both galactic fields and dense stellar clusters.

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