Flares in X-ray transients

I discuss the outburst phenomena in binary X-ray transients, emphasizing the phenomena of the secondary hare, or reflare, based on implicit, time-dependent, irradiated, accretion disk instability models. I examine the role of irradiation, generated from the central compact region and corona, or disk atmosphere, to the disk structure and outburst evolution in black hole X-ray transients. The cause of the primary rise in X-ray nova outburst is plausibly due to the disk instability associated with the ionization of hydrogen and helium, similar to the rise observed in dwarf nova outbursts. The reflare results principally from the so-called "stagnation" phenomena, coupled with the time-dependent effects of indirect irradiation reflected by the corona above the disk. The direct radiation from the central region around the compact object also plays an important role to the reflare. The time-dependent effect of the screening, or shadowing, of the direct if radiation on the disk is included in the modeling. The direct irradiation, unlike in the reflare, makes the disk dimmer in the X-ray quiet state due to shadowing and more depletion of the disk mass. The reflares observed in X-ray transients are short-lived and, furthermore, more pronounced in the radio and optical than in X-rays, suggesting that the phenomena plausibly is local and temporal, associated with the degree of ionization in the outer portion of the disk as modeled here.