  We note that the solution of accretion disk dynamics for an initial
delta-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 outburst quite well. The
Green's function solution of Lynden-Bell & Pringle (1974) is employed for two
differenttime-independent viscosity laws to calculate the expected count rates
of X-ray photons in the Ginga energy 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 the outburst light curves and the source properties during
quiescence support the idea of mass accumulation and the sporadic release of
accumulated mass at the outer disk.
