The change from accretion via a thin disk to a coronal flow: dependence on the viscosity of the hot gas

Abstract

We study the transition from the geometrically thin disk to the hot coronal flow for accretion onto black holes. The efficiency of evaporation determines the truncation of the geometrically thin disk as a function of the black hole mass and the mass flow rate in the outer disk. The physics of the evaporation was already described in detail in earlier work (Meyer et al. 2000b). We show now that the value of the viscosity parameter for the coronal gas has a strong influence on the evaporation efficiency. For smaller values of the viscosity evaporation is less efficient. For a given mass flow rate from outside the geometrically thin disk then extends farther inward. Spectral transitions between soft and hard states are then expected for different mass flow rates in the outer disk. The physics is the same for the cases of stellar and supermassive black holes systems.

6 pages, 1 figure, accepted for publication in A&A

References in corpus (4)

• A Magnetohydrodynamic Nonradiative Accretion Flow in Three Dimensions
• X-Ray spectra from protons illuminating a neutron star
• Truncation of geometrically thin disks around massive black holes in galactic nuclei
• Black hole X-ray transients: mass accumulation in the disk - constraints for the viscosity

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• The Spectral Features of Disk and Corona with Mass Evaporation in the Low/Hard State
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• Accreting corona model of the X-ray variability in soft state X-ray binaries and active galactic nuclei
• Analytical Model of Disk Evaporation and State Transitions in Accreting Black Holes
• On the Change of the Inner Boundary of an Optically Thick Accretion Disk around White Dwarfs Using the Dwarf Nova SS Cyg as an Example
• A cool disk in the Galactic Center?