Light Curves of GRB Optical Flashes

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