A mini-supernova model for optical afterglows of gamma-ray bursts

An energy deposition of ～10⁵⁰ erg into the exterior 10^?3 M⊙ layers of a red giant is calculated to produce an optical phenomenon similar to afterglows of gamma-ray bursts (GRB) recently observed. This mechanism 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 Paczyński, this model does not require huge kinetic energy in the expanding shell to explain optical afterglows of GRB.