  The time evolution of a Gamma-ray burst (GRB) is associated with the
evolution of a supernova remnant (SNR). The time evolution of the flux of a GRB
is modeled introducing a law for the density of the medium in the advancing
layer. The adopted radiative model for the GRB in the various e.m. frequencies
is synchrotron emission. The X-ray ring which appears a few hours after a GRB
is simulated.
