Black-Hole X-Ray Transients: The Effect of Irradiation on Time-Dependent Accretion Disk Structure

Some effects of irradiation on time-dependent accretion-disk models for blackhole X-ray novae are presented. Two types of irradiation are considered: directirradiation from the inner hot disk and indirect irradiation as might bereflected by a corona or chromosphere above the disk. The shadowing effect ofthe time-dependent evolution of the disk height and consequent blocking of theouter disk by the inner and middle portions of the disk from the directirradiation is included. The direct irradiation of the disk by inner layerswhere the soft X-ray flux is generated is found to have only a small effect onthe outer disk because of shadowing. Mild indirect irradiation that flattens,but otherwise does not affect the light curve substantially, still hasinteresting non-linear effects on the structure of the disk as heating andcooling waves propagate. The irradiated disks do not always make simpletransitions between the hot and cold states, but can linger at intermediatetemperatures or even return temporarily to the hot state, depending on theirradiation and the activity in adjacent portions of the disk.Comment: 12 pages, 8 figure