Prompt and early afterglow emission in GRBs

We compare the dynamics of the internal and reverse shocks in the standard scenario of GRBs. We show that the two series of shocks are very similar and should a priori contribute in the same energy range. If internal shocks (IS) are responsible for the gamma-ray emission and the reverse shock (RS) for the early optical signal, the postshock physical conditions must somehow differ between the two cases. We briefly discuss different possibilities for this to occur.