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Title: REVISITING PUTATIVE COOL ACCRETION DISKS IN ULTRALUMINOUS X-RAY SOURCES

Soft, potentially thermal spectral components observed in some ultra-luminous X-ray sources (ULXs) can be fit with models for emission from cool, optically thick accretion disks. If that description is correct, the low temperatures that are observed imply accretion onto 'intermediate-mass' black holes. Subsequent work has found that these components may follow an inverse relationship between luminosity and temperature, implying a non-blackbody origin for this emission. We have re-analyzed numerous XMM-Newton spectra of extreme ULXs. Crucially, observations wherein the source fell on a chip gap were excluded owing to their uncertain flux calibration, and the neutral column density along the line of sight to a given source was jointly determined by multiple spectra. The luminosity of the soft component is found to be positively correlated with temperature, and to be broadly consistent with L∝T {sup 4} in the measured band pass, as per blackbody emission from a standard thin disk. These results are nominally consistent with accretion onto black holes with masses above the range currently known in Galactic X-ray binaries, though there are important caveats. Emission from inhomogeneous or super-Eddington disks may also be consistent with the data.
Authors:
; ; ;  [1] ;  [2] ;  [3] ;  [4]
  1. Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109-1042 (United States)
  2. Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States)
  3. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 OHA (United Kingdom)
  4. Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)
Publication Date:
OSTI Identifier:
22215430
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 776; Journal Issue: 2; 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; CALIBRATION; EMISSION; LUMINOSITY; MASS; ORIGIN; SOFT COMPONENT; SPECTRA; X RADIATION; X-RAY SOURCES