Аннотация:Freddi (Fast Rise Exponential Decay: accretion Disk model
Implementation) solves 1-D evolution equations of the Shakura-Sunyaev
accretion disk. It simulates fast rise exponential decay (FRED) light
curves of low mass X-ray binaries (LMXBs). The basic equation of the
viscous evolution relates the surface density and viscous stresses and
is of diffusion type; evolution of the accretion rate can be found on
solving the equation. The distribution of viscous stresses defines the
emission from the source. The standard model for the accretion disk is
implied; the inner boundary of the disk is at the ISCO or can be
explicitely set. The boundary conditions in the disk are the zero stress
at the inner boundary and the zero accretion rate at the outer boundary.
The conditions are suitable during the outbursts in X-ray binary
transients with black holes. In a binary system, the accretion disk is
radially confined. In Freddi, the outer radius of the disk can be set
explicitely or calculated as the position of the tidal truncation
radius.