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Title: PATCHY ACCRETION DISKS IN ULTRA-LUMINOUS X-RAY SOURCES

The X-ray spectra of the most extreme ultra-luminous X-ray sources—those with L ≥ 10{sup 40} erg s{sup –1}—remain something of a mystery. Spectral roll-over in the 5-10 keV band was originally detected in the deepest XMM-Newton observations of the brightest sources; this is confirmed in subsequent NuSTAR spectra. This emission can be modeled via Comptonization, but with low electron temperatures (kT{sub e} ≅ 2 keV) and high optical depths (τ ≅ 10) that pose numerous difficulties. Moreover, evidence of cooler thermal emission that can be fit with thin disk models persists, even in fits to joint XMM-Newton and NuSTAR observations. Using NGC 1313 X-1 as a test case, we show that a patchy disk with a multiple temperature profile may provide an excellent description of such spectra. In principle, a number of patches within a cool disk might emit over a range of temperatures, but the data only require a two-temperature profile plus standard Comptonization, or three distinct blackbody components. A mechanism such as the photon bubble instability may naturally give rise to a patchy disk profile, and could give rise to super-Eddington luminosities. It is possible, then, that a patchy disk (rather than a disk with a standard single-temperature profile)more » might be a hallmark of accretion disks close to or above the Eddington limit. We discuss further tests of this picture and potential implications for sources such as narrow-line Seyfert-1 galaxies and other low-mass active galactic nuclei.« less
Authors:
 [1] ; ; ;  [2] ; ; ;  [3] ;  [4]
  1. Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109-1042 (United States)
  2. Universite de Toulouse, UPS-OMP, IRAP, F- 31100 Toulouse (France)
  3. Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States)
  4. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)
Publication Date:
OSTI Identifier:
22365917
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 785; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCRETION DISKS; BLACK HOLES; BUBBLES; COSMIC X-RAY SOURCES; ELECTRON TEMPERATURE; GALAXY NUCLEI; KEV RANGE; MASS; POTENTIALS; SEYFERT GALAXIES; STAR CLUSTERS; X RADIATION; X-RAY SPECTRA