Evaporation of Accretion Disks around Black Holes: The Disk-Corona Transition and the Connection to the Advection-dominated Accretion Flow

Abstract

We apply the disk-corona evaporation model (Meyer & Meyer-Hofmeister) originally derived for dwarf novae to black hole systems. This model describes the transition of a thin cool outer disk to a hot coronal flow. The mass accretion rate determines the location of this transition. For a number of well studied black hole binaries we take the mass flow rates derived from a fit of the ADAF model to the observed spectra (for a review see Narayan, Mahadevan, & Quataert) and determine where the transition of accretion via a cool disk to a coronal flow/ADAF would be located for these rates. We compare with the observed location of the inner disk edge, as estimated from the maximum velocity of the $\rm H_\alpha$ emission line. We find that the transition caused by evaporation agrees with this in stellar disks. We also show that the ADAF and the ``thin outer disk + corona'' are compatible in terms of the physics in the transition region.