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 bla ck hole X-ray novae are presented. Two types of irradiation are considered: direct irradiation from the inner hot disk and indirect irradiation as mig ht be reflected by a corona or chromosphere above the disk. The shadowing e ffect of the time-dependent evolution of the disk height and consequent blo cking of the outer disk by the inner and middle portions of the disk from t he direct irradiation is included. The direct irradiation of the disk by in ner layers where the soft X-ray flux is generated is found to have only a s mall effect on the outer disk because of shadowing. Mild indirect irradiati on that flattens, but otherwise does not affect the light curve substantial ly, still has interesting non-linear effects on the structure of the disk a s heating and cooling waves propagate. The irradiated disks do not always m ake simple transitions between the hot and cold states, but can linger at i ntermediate temperatures or even return temporarily to the hot state, depen ding on the irradiation and the activity in adjacent portions of the disk.