The standard model of GRB afterglows assumes that relativistically expanding material is decelerating due to interaction with the surrounding medium. The afterglows are well described by the synchrotron radiation from a forward shock, while the strong optical flash associated with GRB 990123 can be attributed to the emission from a reverse shock. We give a detailed study on the reverse shock emission. The full light curves are calculated for a long and a short GRB cases. We discuss the lack of

more »

... he prompt optical detections by ROTSE for GRB 981121 and GRB 981223.