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The corona contracts in a black-hole transient

The corona contracts in a black-hole transient
The corona contracts in a black-hole transient

The geometry of the accretion flow around stellar-mass black holes can change on timescales of days to months1–3. When a black hole emerges from quiescence (that is, it ‘turns on’ after accreting material from its companion) it has a very hard (high-energy) X-ray spectrum produced by a hot corona4,5 positioned above its accretion disk, and then transitions to a soft (lower-energy) spectrum dominated by emission from the geometrically thin accretion disk, which extends to the innermost stable circular orbit6,7. Much debate persists over how this transition occurs and whether it is driven largely by a reduction in the truncation radius of the disk8,9 or by a reduction in the spatial extent of the corona10,11. Observations of X-ray reverberation lags in supermassive black-hole systems12,13 suggest that the corona is compact and that the disk extends nearly to the central black hole14,15. Observations of stellar-mass black holes, however, reveal equivalent (mass-scaled) reverberation lags that are much larger16, leading to the suggestion that the accretion disk in the hard-X-ray state of stellar-mass black holes is truncated at a few hundreds of gravitational radii from the black hole17,18. Here we report X-ray observations of the black-hole transient MAXI J1820+07019,20. We find that the reverberation time lags between the continuum-emitting corona and the irradiated accretion disk are 6 to 20 times shorter than previously seen. The timescale of the reverberation lags shortens by an order of magnitude over a period of weeks, whereas the shape of the broadened iron K emission line remains remarkably constant. This suggests a reduction in the spatial extent of the corona, rather than a change in the inner edge of the accretion disk.

0028-0836
198-201
Kara, E.
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Steiner, J. F.
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Fabian, A. C.
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Cackett, E. M.
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Uttley, P.
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Remillard, R. A.
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Gendreau, K. C.
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Arzoumanian, Z.
33fc0b56-fcec-49b3-a548-4f600078372e
Altamirano, D.
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Eikenberry, S.
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Enoto, T.
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Homan, J.
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Neilsen, J.
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Stevens, A. L.
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Kara, E.
8c7fd4e8-c791-4d10-b576-63676b056715
Steiner, J. F.
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Fabian, A. C.
b9bef0bc-2ecd-49dc-ab2b-954cabea88ba
Cackett, E. M.
d14dd97a-9acb-4cf2-b9a7-17f9791fdee0
Uttley, P.
db770bd7-d97e-43f5-99d4-a585bccd352a
Remillard, R. A.
87600a84-66cb-400a-97d2-f61e7a7206c3
Gendreau, K. C.
cad26609-b22d-4c1d-ada3-4af51e2cd780
Arzoumanian, Z.
33fc0b56-fcec-49b3-a548-4f600078372e
Altamirano, D.
d5ccdb09-0b71-4303-9538-05b467be075b
Eikenberry, S.
1e439ded-8c26-4664-809a-e817020237c3
Enoto, T.
c5c94b63-52c8-4fd2-bd9e-260a84fff52c
Homan, J.
549baf32-2442-4247-824e-21bb018b05f5
Neilsen, J.
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Stevens, A. L.
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Kara, E., Steiner, J. F., Fabian, A. C., Cackett, E. M., Uttley, P., Remillard, R. A., Gendreau, K. C., Arzoumanian, Z., Altamirano, D., Eikenberry, S., Enoto, T., Homan, J., Neilsen, J. and Stevens, A. L. (2019) The corona contracts in a black-hole transient. Nature, 565 (7738), 198-201. (doi:10.1038/s41586-018-0803-x).

Record type: Letter

Abstract

The geometry of the accretion flow around stellar-mass black holes can change on timescales of days to months1–3. When a black hole emerges from quiescence (that is, it ‘turns on’ after accreting material from its companion) it has a very hard (high-energy) X-ray spectrum produced by a hot corona4,5 positioned above its accretion disk, and then transitions to a soft (lower-energy) spectrum dominated by emission from the geometrically thin accretion disk, which extends to the innermost stable circular orbit6,7. Much debate persists over how this transition occurs and whether it is driven largely by a reduction in the truncation radius of the disk8,9 or by a reduction in the spatial extent of the corona10,11. Observations of X-ray reverberation lags in supermassive black-hole systems12,13 suggest that the corona is compact and that the disk extends nearly to the central black hole14,15. Observations of stellar-mass black holes, however, reveal equivalent (mass-scaled) reverberation lags that are much larger16, leading to the suggestion that the accretion disk in the hard-X-ray state of stellar-mass black holes is truncated at a few hundreds of gravitational radii from the black hole17,18. Here we report X-ray observations of the black-hole transient MAXI J1820+07019,20. We find that the reverberation time lags between the continuum-emitting corona and the irradiated accretion disk are 6 to 20 times shorter than previously seen. The timescale of the reverberation lags shortens by an order of magnitude over a period of weeks, whereas the shape of the broadened iron K emission line remains remarkably constant. This suggests a reduction in the spatial extent of the corona, rather than a change in the inner edge of the accretion disk.

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The corona contracts in a new black hole transient - Accepted Manuscript
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Accepted/In Press date: 17 October 2018
e-pub ahead of print date: 9 January 2019
Published date: 10 January 2019

Identifiers

Local EPrints ID: 427946
URI: https://eprints.soton.ac.uk/id/eprint/427946
ISSN: 0028-0836
PURE UUID: 827e4b0b-9841-4a3c-a773-8c4885d24945
ORCID for D. Altamirano: ORCID iD orcid.org/0000-0002-3422-0074

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Date deposited: 05 Feb 2019 17:30
Last modified: 14 Mar 2019 01:33

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Contributors

Author: E. Kara
Author: J. F. Steiner
Author: A. C. Fabian
Author: E. M. Cackett
Author: P. Uttley
Author: R. A. Remillard
Author: K. C. Gendreau
Author: Z. Arzoumanian
Author: D. Altamirano ORCID iD
Author: S. Eikenberry
Author: T. Enoto
Author: J. Homan
Author: J. Neilsen
Author: A. L. Stevens

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