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Spectral Evolution of the Ultraluminous X-Ray Sources M82 X-1 and X-2

Brightman, Murray and Walton, Dominic J. and Xu, Yanjun and Earnshaw, Hannah P. and Harrison, Fiona A. and Stern, Daniel and Barret, Didier (2020) Spectral Evolution of the Ultraluminous X-Ray Sources M82 X-1 and X-2. Astrophysical Journal, 889 (1). Art. No. 71. ISSN 1538-4357. doi:10.3847/1538-4357/ab629a.

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M82 hosts two well-known ultraluminous X-ray sources (ULXs). X-1, an intermediate-mass black hole (IMBH) candidate, and X-2, an ultraluminous X-ray pulsar. Here, we present a broadband X-ray spectral analysis of both sources based on 10 simultaneous observations made with Chandra and NuSTAR. Chandra provides the high spatial resolution to resolve the crowded field in the 0.5–8 keV band, and NuSTAR provides the sensitive hard X-ray spectral data, extending the bandpass of our study above 10 keV. These observations, taken in 2015–2016, cover a period of flaring from X-1, allowing us to study the spectral evolution of this source with luminosity. During four of these observations, X-2 was found to be at a low flux level, allowing an unambiguous view of the emission from X-1. We find that the broadband X-ray emission from X-1 is consistent with that seen in other ULXs observed in detail with NuSTAR, with a spectrum that includes a broadened disk-like component and a high-energy tail. We find that the luminosity of the disk scales with inner disk temperature as L ∝ T^(−3/2), contrary to expectations of a standard accretion disk and previous results. These findings rule out a thermal state for sub-Eddington accretion, and therefore do not support M82 X-1 as an IMBH candidate. We also find evidence that the neutral column density of the material in the line of sight increases with L_X, perhaps due to an increased mass outflow with accretion rate. For X-2, we do not find any significant spectral evolution, but we find the spectral parameters of the phase-averaged broadband emission are consistent with the pulsed emission at the highest X-ray luminosities.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Brightman, Murray0000-0002-8147-2602
Walton, Dominic J.0000-0001-5819-3552
Xu, Yanjun0000-0003-2443-3698
Earnshaw, Hannah P.0000-0001-5857-5622
Harrison, Fiona A.0000-0003-2992-8024
Stern, Daniel0000-0003-2686-9241
Barret, Didier0000-0002-0393-9190
Additional Information:© 2020 The Author(s). Published by IOP Publishing Ltd on behalf of the American Astronomical Society. Received 2019 September 18; revised 2019 December 5; accepted 2019 December 15; published 2020 January 27. This research has made use of data obtained with NuSTAR, 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). Support for this work was provided by the National Aeronautics and Space Administration through Chandra Award Number GO6-17080X issued by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the National Aeronautics Space Administration under contract NAS8-03060. This research has made use of software provided by the Chandra X-ray Center (CXC) in the application package ciao. We also acknowledge the use of public data from the Swift data archive. D.J.W. acknowledges support from an STFC Ernest Rutherford Fellowship. Facilities: Chandra (ACIS) - , NuSTAR - , Swift (XRT). -
Group:NuSTAR, Space Radiation Laboratory, Astronomy Department
Funding AgencyGrant Number
Science and Technology Facilities Council (STFC)UNSPECIFIED
Subject Keywords:Astrophysical black holes; Intermediate-mass black holes; Stellar mass black holes; X-ray point sources; X-ray sources; Pulsars; Neutron stars
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Astrophysical black holes (98); Intermediate-mass black holes (816); Stellar mass black holes (1611); X-ray point sources (1270); X-ray sources (1822); Pulsars (1306); Neutron stars (1108)
Record Number:CaltechAUTHORS:20200127-074253356
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Official Citation:Murray Brightman et al 2020 ApJ 889 71
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:100924
Deposited By: Tony Diaz
Deposited On:28 Jan 2020 18:53
Last Modified:16 Nov 2021 17:57

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