A mini-supernova model for optical afterglows of GRB

An energy deposition of \sim 10^{50} ergs into the exterior 10^{-3} M_\sun layers of a red giant is calculated to produce an optical phenomenon similar to afterglows of gamma-ray bursts (GRB) recently observed. This model can be realized if a GRB is generated by some mechanism in a close binary system. In contrast to a ``hypernova'' scenario for GRB recently proposed by Paczy\'nski (1997), this model does not require a huge kinetic energy of the expanding shell to explain optical afterglows of GRB.