Time-delays between the soft and hard X-ray bands in GRS 1915 + 105

Abstract

The hard X-ray light curves exhibit delays of ∼1 s with respect to the soft X-ray light curves when the microquasar GRS 1915 + 105 is in the state of frequent, regular outbursts (states ρ and κ of Belloni et al.). Such outbursts are supposed to be driven by the radiation-pressure instability of the inner disc parts. The hard X-ray delays are then caused by the time needed for the corona to adjust to the changing conditions in the underlying disc. We support this claim by the computation of the time-evolution of the disc, including a non-stationary evaporation of the disc and mass exchange with the corona.