ON THE OUTBURST LIGHT CURVES OF SOFT-X-RAY TRANSIENTS AS RESPONSE OF THE ACCRETION DISK TO MASS DEPOSITION

We note that the solution of accretion disk dynamics for an initial de lta-function mass distribution gives a light curve that fits both the rise and the decay pattern of the outburst light curves of black-hole Soft X-ray transients (BSXTs) until the onset of the first mini outbur st quite well. The Green's function solution of Lynden-Bell & Pringle (1974) is employed for two different time-independent viscosity laws t o calculate the expected count rates of X-ray photons in the Ginga ene rgy bands as a function of time. For both models basic characteristics of the outburst light curves of two typical sources GS 2000+25 and GS /GRS 1124-68 are reproduced together with plausible values of the thin disk parameter alpha and the recurrence times. This agreement with th e outburst light curves and the source properties during quiescence su pport the idea of mass accumulation and the sporadic release of accumu lated mass at the outer disk.