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The corona contracts in a black-hole transient
E Kara1,2,3,4, J F Steiner5, A C Fabian6
1University of Maryland, College Park, MD, USA. ekara@astro.umd.edu.
Nature
|January 11, 2019
Summary
Stellar-mass black hole accretion disks show shorter X-ray reverberation lags, indicating a shrinking corona. This challenges previous models suggesting disk truncation as the primary driver of spectral changes.
Area of Science:
- * Astrophysics
- * High-energy astrophysics
- * Black hole accretion physics
Background:
- * Accretion flow geometry around stellar-mass black holes changes on monthly timescales.
- * Spectral transitions from hard (hot corona) to soft (thin disk) states are debated.
- * X-ray reverberation lags in supermassive black holes suggest compact coronas and near-black hole disks.
Purpose of the Study:
- * To investigate the geometry of accretion flows in stellar-mass black holes.
- * To determine the drivers of spectral transitions in black hole accretion states.
- * To resolve the debate on disk truncation versus corona shrinkage.
Main Methods:
- * X-ray observations of the black-hole transient MAXI J1820+070.
- * Analysis of reverberation time lags between the corona and accretion disk.
- * Monitoring of the broadened iron K emission line profile.
Main Results:
- * Reverberation time lags were 6 to 20 times shorter than previously observed.
- * Lag timescales decreased by an order of magnitude over weeks.
- * The iron K emission line shape remained constant during the observation period.
Conclusions:
- * Findings suggest a reduction in the spatial extent of the corona.
- * This contradicts models emphasizing changes in the accretion disk's inner edge.
- * The study provides new insights into black hole accretion dynamics.
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