New solution to viscous evolution of accretion disks in binary systems

The analytical investigation of time-dependent accretion in disks is carrie d out. We consider a time-dependent disk in a binary system at outburst whi ch has a fixed tidally-truncated outer radius. The standard model (Shakura- Sunyaev) of the di sk is considered. The vertical structure of the disk is accurately described in two regimes of opacity: Thomson and free-free. The fully analytical solutions are obtained, characterized by power-law variati ons of accretion rate with time. The solutions supply asymptotic descriptio n of the disk evolution in flaring sources in the periods after outbursts w hile the disk is fully ionized. The X-ray flux of multicolor (black-body) a lpha-disk is obtained as varying quasi-exponentially. The application to X- ray novae is briefly discussed concerning the observed faster-than-power de cays of X-ray light curves. The case of time-dependent advective disk when the exponential variations of accretion rate can occur is discussed.