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The soft state of the black hole transient source MAXI J1820+070: emission from the edge of the plunge region?

Fabian, A. C. and Buisson, D. J. and Kosec, P. and Reynolds, C. S. and Wilkins, D. R. and Tomsick, J. A. and Walton, D. J. and Gandhi, P. and Altamirano, D. and Arzoumanian, Z. and Cackett, E. M. and Dyda, S. and García, J. A. and Gendreau, K. C. and Grefenstette, B. W. and Homan, J. and Kara, E. and Ludlam, R. M. and Miller, J. M. and Steiner, J. F. (2020) The soft state of the black hole transient source MAXI J1820+070: emission from the edge of the plunge region? Monthly Notices of the Royal Astronomical Society, 493 (4). pp. 5389-5396. ISSN 0035-8711.

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The Galactic black hole X-ray binary MAXI J1820+070 had a bright outburst in 2018 when it became the second brightest X-ray source in the sky. It was too bright for X-ray CCD instruments such as XMM–Newton and Chandra, but was well observed by photon-counting instruments such as Neutron star Inner Composition Explorer (NICER) and Nuclear Spectroscopic Telescope Array(NuSTAR). We report here on the discovery of an excess-emission component during the soft state. It is best modelled with a blackbody spectrum in addition to the regular disc emission, modelled as either diskbb or kerrbb. Its temperature varies from about 0.9 to 1.1 keV, which is about 30–80 per cent higher than the inner disc temperature of diskbb. Its flux varies between 4 and 12 per cent of the disc flux. Simulations of magnetized accretion discs have predicted the possibility of excess emission associated with a non-zero torque at the innermost stable circular orbit (ISCO) about the black hole, which, from other NuSTAR studies, lies at about 5 gravitational radii or about 60 km (for a black hole, mass is 8M⊙). In this case, the emitting region at the ISCO has a width varying between 1.3 and 4.6 km and would encompass the start of the plunge region where matter begins to fall freely into the black hole.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Fabian, A. C.0000-0002-9378-4072
Wilkins, D. R.0000-0002-4794-5998
Tomsick, J. A.0000-0001-5506-9855
Walton, D. J.0000-0001-5819-3552
Gandhi, P.0000-0003-3105-2615
Altamirano, D.0000-0002-3422-0074
Cackett, E. M.0000-0002-8294-9281
García, J. A.0000-0003-3828-2448
Grefenstette, B. W.0000-0002-1984-2932
Homan, J.0000-0001-8371-2713
Kara, E.0000-0003-0172-0854
Ludlam, R. M.0000-0002-8961-939X
Steiner, J. F.0000-0002-5872-6061
Additional Information:© 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2020 February 21. Received 2020 February 19; in original form 2019 November 5. Published: 27 February 2020. ACF and SD acknowledge support from European Research Council Advanced Grant FEEDBACK, and DRW is supported by NASA through Einstein Postdoctoral Fellowship grant number PF6-170160, awarded by the Chandra X-ray Center, operated by the Smithsonian Astrophysical Observatory for NASA under contract NAS8-03060.340442. CSR thanks the UK Science and Technology Facilities Council (STFC) for support under the New Applicant grant ST/R000867/1, and the European Research Council (ERC) for support under the European Union’s Horizon 2020 research and innovation programme (grant 834203).
Funding AgencyGrant Number
European Research Council (ERC)FEEDBACK
NASA Einstein FellowshipPF6-170160
Science and Technology Facilities Council (STFC)ST/R000867/1
European Research Council (ERC)834203
Subject Keywords:accretion, accretion discs –X-rays: binaries – black hole physics
Issue or Number:4
Record Number:CaltechAUTHORS:20200415-075915052
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Official Citation:A C Fabian, D J Buisson, P Kosec, C S Reynolds, D R Wilkins, J A Tomsick, D J Walton, P Gandhi, D Altamirano, Z Arzoumanian, E M Cackett, S Dyda, J A Garcia, K C Gendreau, B W Grefenstette, J Homan, E Kara, R M Ludlam, J M Miller, J F Steiner, The soft state of the black hole transient source MAXI J1820+070: emission from the edge of the plunge region?, Monthly Notices of the Royal Astronomical Society, Volume 493, Issue 4, April 2020, Pages 5389–5396,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:102545
Deposited By: Tony Diaz
Deposited On:15 Apr 2020 16:32
Last Modified:15 Apr 2020 16:32

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