The corona contracts in a black-hole transient

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

doi:10.1038/s41586-018-0803-x

The corona contracts in a black-hole transient

Nature. 2019 Jan;565(7738):198-201. doi: 10.1038/s41586-018-0803-x. Epub 2019 Jan 9.

Authors

E Kara^{1

2

3

4}, J F Steiner⁵, A C Fabian⁶, E M Cackett⁷, P Uttley⁸, R A Remillard⁵, K C Gendreau⁹, Z Arzoumanian⁹, D Altamirano¹⁰, S Eikenberry^{11

12}, T Enoto¹³, J Homan^{14

15}, J Neilsen¹⁶, A L Stevens¹⁷

Affiliations

¹ University of Maryland, College Park, MD, USA. ekara@astro.umd.edu.
² NASA Goddard Space Flight Center, Greenbelt, MD, USA. ekara@astro.umd.edu.
³ Joint Space Science Institute, University of Maryland, College Park, MD, USA. ekara@astro.umd.edu.
⁴ MIT Kavli Institute for Astrophysics and Space Research, Cambridge, MA, USA. ekara@astro.umd.edu.
⁵ MIT Kavli Institute for Astrophysics and Space Research, Cambridge, MA, USA.
⁶ Institute of Astronomy, Cambridge, UK.
⁷ Wayne State University, Department of Physics and Astronomy, Detroit, MI, USA.
⁸ Anton Pannekoek Institute for Astronomy, University of Amsterdam, Amsterdam, The Netherlands.
⁹ NASA Goddard Space Flight Center, Greenbelt, MD, USA.
¹⁰ School of Physics and Astronomy, University of Southampton, Southampton, UK.
¹¹ Department of Astronomy, University of Florida, Gainesville, FL, USA.
¹² Department of Physics, University of Florida, Gainesville, FL, USA.
¹³ Hakubi Center for Advanced Research and Department of Astronomy, Kyoto University, Kyoto, Japan.
¹⁴ Eureka Scientific, Oakland, CA, USA.
¹⁵ SRON, Netherlands Institute for Space Research, Utrecht, The Netherlands.
¹⁶ Villanova University, Department of Physics, Villanova, PA, USA.
¹⁷ Department of Physics and Astronomy, Michigan State University, East Lansing, MI, USA.

PMID: 30626944
DOI: 10.1038/s41586-018-0803-x

Abstract

The geometry of the accretion flow around stellar-mass black holes can change on timescales of days to months^1-3. 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 corona^4,5 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 orbit^6,7. Much debate persists over how this transition occurs and whether it is driven largely by a reduction in the truncation radius of the disk^8,9 or by a reduction in the spatial extent of the corona^10,11. Observations of X-ray reverberation lags in supermassive black-hole systems^12,13 suggest that the corona is compact and that the disk extends nearly to the central black hole^14,15. 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 hole^17,18. Here we report X-ray observations of the black-hole transient MAXI J1820+070^19,20. 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.

Publication types

Research Support, U.S. Gov't, Non-P.H.S.