Andrew D. Sutton
Irradiated, colour-temperature-corrected accretion discs in ultraluminous X-ray sources
Sutton, Andrew D.; Done, Chris; Roberts, Timothy P.
Authors
Professor Christine Done chris.done@durham.ac.uk
Professor
Professor Tim Roberts t.p.roberts@durham.ac.uk
Professor
Abstract
Although attempts have been made to constrain the stellar types of optical counterparts to ultraluminous X-ray sources (ULXs), the detection of optical variability instead suggests that they may be dominated by reprocessed emission from X-rays which irradiate the outer accretion disc. Here, we report results from a combined X-ray and optical spectral study of a sample of ULXs, which were selected for having broadened disc-like X-ray spectra and known optical counterparts. We simultaneously fit optical and X-ray data from ULXs with a new spectral model of emission from an irradiated, colour-temperature-corrected accretion disc around a black hole, with a central Comptonizing corona. We find that the ULXs require reprocessing fractions of ∼10−3, which is similar to sub-Eddington thermal dominant state black hole binaries (BHBs), but less than has been reported for ULXs with soft ultraluminous X-ray spectra. We suggest that the reprocessing fraction may be due to the opposing effects of self-shielding in a geometrically thick supercritical accretion disc and reflection from far above the central black hole by optically thin material ejected in a natal super-Eddington wind. Then, the higher reprocessing fractions reported for ULXs with wind-dominated X-ray spectra may be due to enhanced scattering on to the outer disc via the stronger wind in these objects. Alternatively, the accretion discs in these ULXs may not be particularly geometrically thick, rather they may be similar in this regard to the thermal dominant state BHBs.
Citation
Sutton, A. D., Done, C., & Roberts, T. P. (2014). Irradiated, colour-temperature-corrected accretion discs in ultraluminous X-ray sources. Monthly Notices of the Royal Astronomical Society, 444(3), 2415-2427. https://doi.org/10.1093/mnras/stu1597
Journal Article Type | Article |
---|---|
Acceptance Date | Aug 5, 2014 |
Online Publication Date | Sep 10, 2014 |
Publication Date | Nov 1, 2014 |
Deposit Date | Sep 19, 2014 |
Publicly Available Date | Sep 19, 2014 |
Journal | Monthly Notices of the Royal Astronomical Society |
Print ISSN | 0035-8711 |
Electronic ISSN | 1365-2966 |
Publisher | Royal Astronomical Society |
Peer Reviewed | Peer Reviewed |
Volume | 444 |
Issue | 3 |
Pages | 2415-2427 |
DOI | https://doi.org/10.1093/mnras/stu1597 |
Keywords | Accretion, Accretion discs, Black hole physics, X rays: binaries, X rays: galaxies. |
Related Public URLs | http://uk.arxiv.org/pdf/1408.2375 |
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Copyright Statement
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
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