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Maxi J1820+070 with Nustar I. An increase in variability frequency but a stable reflection spectrum: Coronal properties and implications for the inner disc in black hole binaries

Maxi J1820+070 with Nustar I. An increase in variability frequency but a stable reflection spectrum: Coronal properties and implications for the inner disc in black hole binaries
Maxi J1820+070 with Nustar I. An increase in variability frequency but a stable reflection spectrum: Coronal properties and implications for the inner disc in black hole binaries
MAXI J1820+070 (optical counterpart ASASSN-18ey) is a black hole candidate discovered through its recent very bright outburst. The low extinction column and long duration at high flux allow detailed measurements of the accretion process to be made. In this work, we compare the evolution of X-ray spectral and timing properties through the initial hard state of the outburst. We show that the inner accretion disc, as measured by relativistic reflection, remains steady throughout this period of the outburst. Nevertheless, subtle spectral variability is observed, which is well explained by a change in coronal geometry. However, characteristic features of the temporal variability – low-frequency roll-over and quasi-periodic oscillation frequency – increase drastically in frequency, as the outburst proceeds. This suggests that the variability time-scales are governed by coronal conditions rather than solely by the inner disc radius. We also find a strong correlation between X-ray luminosity and coronal temperature. This can be explained by electron pair production with a changing effective radius and a non-thermal electron fraction of ∼20 per cent.
0035-8711
1350-1362
Buisson, D.J.K.
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Fabian, A.C.
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Barret, D.
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Fürst, F.
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Gandhi, P.
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García, J.A.
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Kara, E.
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Madsen, K.K.
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Miller, J.M.
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Parker, M.L.
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Shaw, A.W.
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Tomsick, J.A.
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Walton, D.J.
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Buisson, D.J.K.
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Fabian, A.C.
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Barret, D.
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Fürst, F.
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Gandhi, P.
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García, J.A.
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Kara, E.
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Madsen, K.K.
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Miller, J.M.
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Parker, M.L.
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Shaw, A.W.
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Tomsick, J.A.
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Walton, D.J.
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Buisson, D.J.K., Fabian, A.C., Barret, D., Fürst, F., Gandhi, P., García, J.A., Kara, E., Madsen, K.K., Miller, J.M., Parker, M.L., Shaw, A.W., Tomsick, J.A. and Walton, D.J. (2019) Maxi J1820+070 with Nustar I. An increase in variability frequency but a stable reflection spectrum: Coronal properties and implications for the inner disc in black hole binaries. Monthly Notices of the Royal Astronomical Society, 490 (1), 1350-1362. (doi:10.1093/mnras/stz2681). (In Press)

Record type: Article

Abstract

MAXI J1820+070 (optical counterpart ASASSN-18ey) is a black hole candidate discovered through its recent very bright outburst. The low extinction column and long duration at high flux allow detailed measurements of the accretion process to be made. In this work, we compare the evolution of X-ray spectral and timing properties through the initial hard state of the outburst. We show that the inner accretion disc, as measured by relativistic reflection, remains steady throughout this period of the outburst. Nevertheless, subtle spectral variability is observed, which is well explained by a change in coronal geometry. However, characteristic features of the temporal variability – low-frequency roll-over and quasi-periodic oscillation frequency – increase drastically in frequency, as the outburst proceeds. This suggests that the variability time-scales are governed by coronal conditions rather than solely by the inner disc radius. We also find a strong correlation between X-ray luminosity and coronal temperature. This can be explained by electron pair production with a changing effective radius and a non-thermal electron fraction of ∼20 per cent.

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Maxi J1820-070 with Nustar I. An increase in variability frequency but a stable reflection spectrum-Coronal properties and implications for the inner disc in black hole binaries - Accepted Manuscript
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Accepted/In Press date: 20 September 2019
Additional Information: arXiv is AM

Identifiers

Local EPrints ID: 436454
URI: http://eprints.soton.ac.uk/id/eprint/436454
ISSN: 0035-8711
PURE UUID: f5f03c23-8c52-471d-a1d0-e606b4c1f7c1
ORCID for P. Gandhi: ORCID iD orcid.org/0000-0003-3105-2615

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Date deposited: 11 Dec 2019 17:30
Last modified: 07 Oct 2020 02:06

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Contributors

Author: D.J.K. Buisson
Author: A.C. Fabian
Author: D. Barret
Author: F. Fürst
Author: P. Gandhi ORCID iD
Author: J.A. García
Author: E. Kara
Author: K.K. Madsen
Author: J.M. Miller
Author: M.L. Parker
Author: A.W. Shaw
Author: J.A. Tomsick
Author: D.J. Walton

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