Аннотация:We review the properties of analytical solutions to the basic equation of time-dependent accretion. A new analytical solution describing a time-dependent disk in a binary system at outburst which has a fixed tidally-truncated outer radius is applied to 1975 X-ray Nova burst of A0620-00. The X-ray flux of multicolor (black body) alpha-disk decays quasi-exponentially with time. Modeling of the light curves of A0620-00 before and after the second maximum is presented.