  Analytical investigation of time-dependent accretion in disks is carried out.
We consider a time-dependent disk in a binary system at outburst which has a
fixed tidally-truncated outer radius. The standard Shakura-Sunyaev model of the
disk is considered. The vertical structure of the disk is accurately described
in two regimes of opacity: Thomson and free-free. Fully analytical solutions
are obtained, characterized by power-law variations of accretion rate with
time. The solutions supply asymptotic description of disk evolution in flaring
sources in the periods after outbursts while the disk is fully ionized. The
X-ray flux of multicolor (black-body) alpha-disk is obtained as varying
quasi-exponentially. Application to X-ray novae is briefly discussed concerning
the observed faster-than-power decays of X-ray light curves. The case of
time-dependent advective disk when the exponential variations of accretion rate
can occur is discussed.
