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A broadband X-ray spectral study of the intermediate-mass black hole candidate M82 X-1 with NuSTAR, Chandra and Swift

Brightman, Murray and Harrison, Fiona A. and Barret, Didier and Davis, Shane W. and Fürst, Felix and Madsen, Kristin K. and Middleton, Matthew and Miller, Jon M. and Stern, Daniel and Tao, Lian and Walton, Dominic J. (2016) A broadband X-ray spectral study of the intermediate-mass black hole candidate M82 X-1 with NuSTAR, Chandra and Swift. Astrophysical Journal, 829 (1). Art. No. 28. ISSN 0004-637X. http://resolver.caltech.edu/CaltechAUTHORS:20160928-115009615

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Abstract

M82 X-1 is one of the brightest ultraluminous X-ray sources (ULXs) known, which, assuming Eddington-limited accretion and other considerations, makes it one of the best intermediate-mass black-hole (IMBH) candidates. However, the ULX may still be explained by super-Eddington accretion onto a stellar remnant black hole. We present simultaneous NuSTAR, Chandra, and Swift/XRT observations during the peak of a flaring episode with the aim of modeling the emission of M82 X-1 and yielding insights into its nature. We find that thin accretion disk models all require accretion rates at or above the Eddington limit in order to reproduce the spectral shape, given a range of black-hole masses and spins. Since at these high Eddington ratios the thin-disk model breaks down due to radial advection in the disk, we discard the results of the thin-disk models as unphysical. We find that the temperature profile as a function of disk radius (T(r) ∝ r^(-p)) is significantly flatter (p = 0.55_(-0.04)^(+0.07)) than expected for a standard thin disk (p = 0.75). A flatter profile is instead characteristic of a slim disk, which is highly suggestive of super-Eddington accretion. Furthermore, radiation hydrodynamical simulations of super-Eddington accretion have shown that the predicted spectra of these systems are very similar to what we observe for M82 X-1. We therefore conclude that M82 X-1 is a super-Eddington accretor. Our mass estimates inferred from the inner disk radius imply a stellar remnant black hole (M_(BH) = 26_(-6)^(+9 M_⊙) when assuming zero spin and face-on inclination, or an IMBH for maximal spin and a highly inclined disk.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.3847/0004-637X/829/1/28DOIArticle
http://iopscience.iop.org/article/10.3847/0004-637X/829/1/28/metaPublisherArticle
https://arxiv.org/abs/1607.03903arXivDiscussion Paper
ORCID:
AuthorORCID
Harrison, Fiona A.0000-0003-2992-8024
Madsen, Kristin K.0000-0003-1252-4891
Stern, Daniel0000-0003-2686-9241
Walton, Dominic J.0000-0001-5819-3552
Additional Information:© 2016 American Astronomical Society. Received 2016 June 2; revised 2016 July 11; accepted 2016 July 13; published 2016 September 20. This work made use of Director's Discretionary Time on Chandra, for which we thank Belinda Wilkes for approving and the Chandra X-ray Center for implementing. We also use Director's Discretionary Time on NuSTAR, for which we thank Fiona Harrison for approving and the NuSTAR SOC for co-ordinating with Chandra. The NuSTAR mission is a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by NASA. We thank the NuSTAR Operations, Software and Calibration teams for support with the execution and analysis of these observations. This research has made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA). A.Z. acknowledges funding from the European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013)/ERC Grant Agreement n. 617001. Facilities: Chandra (ACIS) - , NuSTAR - , Swift (XRT).
Group:NuSTAR, Space Radiation Laboratory
Funders:
Funding AgencyGrant Number
European Research Council (ERC)617001
Subject Keywords:black hole physics; X-rays: binaries; X-rays: individual (M82 X-1)
Record Number:CaltechAUTHORS:20160928-115009615
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20160928-115009615
Official Citation:Murray Brightman et al 2016 ApJ 829 28
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:70639
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:28 Sep 2016 22:24
Last Modified:30 Nov 2017 16:54

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