Vertical structure of the accreting two-temperature corona and the transition to an ADAF

Abstract

We investigate the model of the disc/corona accretion flow around the black hole. The model, parameterized by the total (i.e. disk plus corona) accretion rate, $\dot m$, mass of the black hole, $M$ and the viscosity parameter, $α$, uniquely determines the fraction of energy released in the corona as a function of radius and, in particular, the transition radius to the single-phase ADAF flow. Self-consistent solutions with the mass exchange between phases display radial dependence of the parameters. This model reproduces all characteristic luminosity states of accretion black hole without any additional ad hoc assumptions. In particular. the mechanism of the disk evaporation leads to a new, almost horizontal branch on the accretion flow's stability curve (i.e. the dependence of accretion rate on surface density) at the critical accretion rate.