Analytical Model of Disk Evaporation and State Transitions in Accreting Black Holes
Abstract

State transitions in black hole X-ray binaries are likely caused by gas evaporation from a thin accretion disk into a hot corona. We present a height-integrated version of this process, which is suitable for analytical and numerical studies. With radiusrscaled to Schwarzschild units and coronal mass accretion rate$ṁc$to Eddington units, the results of the model are independent of black hole mass. State transitions should thus be similar in X-ray binaries and an active galactic nucleus. The corona solution consists of two power-law segments separated at a break radiusrb∼ 103(α/0.3)−2, whereαis the viscosity parameter. Gas evaporates from the disk to the corona forr>rb, and condenses back forr<rb. Atrb,$ṁc$reaches its maximum,$ṁc,max≈0.02(α/0.3)3$. If atrrbthe thin disk accretes with$ṁd, then the disk evaporates fully before reachingrb, giving the hard state. Otherwise, the disk survives at all radii, giving the thermal state. While the basic model considers only bremsstrahlung cooling and viscous heating, we also discuss a more realistic model that includes Compton cooling and direct coronal heating by energy transport from the disk. Solutions are again independent of black hole mass, andrbremains more »

Authors:
;
Award ID(s):
Publication Date:
NSF-PAR ID:
10367979
Journal Name:
The Astrophysical Journal
Volume:
932
Issue:
2
Page Range or eLocation-ID:
Article No. 97
ISSN:
0004-637X
Publisher:
DOI PREFIX: 10.3847
National Science Foundation
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