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Diagnosing the accretion flow in ultraluminous X-ray sources using soft X-ray atomic features

Middleton, Matthew J. and Walton, Dominic J. and Fabian, Andrew and Roberts, Timothy P. and Heil, Lucy and Pinto, Ciro and Anderson, Gemma and Sutton, Andrew (2015) Diagnosing the accretion flow in ultraluminous X-ray sources using soft X-ray atomic features. Monthly Notices of the Royal Astronomical Society, 454 (3). pp. 3134-3142. ISSN 0035-8711.

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The lack of unambiguous detections of atomic features in the X-ray spectra of ultraluminous X-ray sources (ULXs) has proven a hindrance in diagnosing the nature of the accretion flow. The possible association of spectral residuals at soft energies with atomic features seen in absorption and/or emission and potentially broadened by velocity dispersion could therefore hold the key to understanding much about these enigmatic sources. Here we show for the first time that such residuals are seen in several sources and appear extremely similar in shape, implying a common origin. Via simple arguments we assert that emission from extreme colliding winds, absorption in a shell of material associated with the ULX nebula and thermal plasma emission associated with star formation are all highly unlikely to provide an origin. Whilst CCD spectra lack the energy resolution necessary to directly determine the nature of the features (i.e. formed of a complex of narrow lines or intrinsically broad lines), studying the evolution of the residuals with underlying spectral shape allows for an important, indirect test for their origin. The ULX NGC 1313 X-1 provides the best opportunity to perform such a test due to the dynamic range in spectral hardness provided by archival observations. We show through highly simplified spectral modelling that the strength of the features (in either absorption or emission) appears to anticorrelate with spectral hardness, which would rule out an origin via reflection of a primary continuum and instead supports a picture of atomic transitions in a wind or nearby material associated with such an outflow.

Item Type:Article
Related URLs:
URLURL TypeDescription
Middleton, Matthew J.0000-0002-8183-2970
Walton, Dominic J.0000-0001-5819-3552
Fabian, Andrew0000-0002-9378-4072
Roberts, Timothy P.0000-0001-8252-6337
Pinto, Ciro0000-0003-2532-7379
Additional Information:© 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2015 September 21. Received 2015 September 21; in original form 2015 June 4. First published online October 17, 2015. The authors thank the anonymous referee for their suggestions and Simon Vaughan for helpful discussion. MJM appreciates support from ERC grant 340442, DJW is supported by ORAU under the NASA Postdoctoral programme at the NASA Jet Propulsion Laboratory. TPR was funded as part of the STFC consolidated grant ST/L00075X/1. This work is based on observations obtained with XMM–Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.
Funding AgencyGrant Number
European Research Council (ERC)340442
NASA Postdoctoral ProgramUNSPECIFIED
Science and Technology Facilities Council (STFC)ST/L00075X/1
Subject Keywords:accretion, accretion discs –X-rays: binaries
Issue or Number:3
Record Number:CaltechAUTHORS:20160205-131858163
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Official Citation:Matthew J. Middleton, Dominic J. Walton, Andrew Fabian, Timothy P. Roberts, Lucy Heil, Ciro Pinto, Gemma Anderson, and Andrew Sutton Diagnosing the accretion flow in ultraluminous X-ray sources using soft X-ray atomic features MNRAS (December 11, 2015) Vol. 454 3134-3142 doi:10.1093/mnras/stv2214 First published online October 17, 2015
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:64280
Deposited By: George Porter
Deposited On:08 Feb 2016 17:49
Last Modified:09 Mar 2020 13:19

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