The existence of inner cool disks in the low hard state of accreting black holes

We present our recent study on the condensation of matter from a Corona to a Cool, optically thick inner disk for black hole X-ray transient systems in the low hard state. A simple model for the exchange of energy and mass between the Corona and disk promoted by thermal conduction is introduced. It is found that a weak, condensation-fed inner disk can be present in the low hard state of black hole transients for a range of luminosities which depend on the magnitude of the Corona viscosity. For alpha similar to 0.1 - 0.4, an inner disk can exist for luminosities in the range of 0.001-0.02 Eddington luminosity. The model is applied to the black hole candidate sources OX 339-4 in the low hard state for which evidence is provided pointing to the possible existence of a cool inner disk (Miller et al. 2006a). It is found that Compton cooling processes are important in the condensation, leading to the maintenance of cool inner disks in GX 339-4 in its low hard state.