Bumps in the optical afterglow of GRB 030329: refreshed shocks and evidence for internal shocks in GRBs?

The afterglow of GRB 030329 presents a high variability, made of approximately constant duration bumps, which we explain by a series of late energy injections from slow shells (refreshed shocks). We model the GRB 030329 afterglow assuming that the central source first emits rapid material (Gamma similar to 100) immediately followed by slower one (Gamma similar to 10), which can catch up with the rapid material when it has been decelerated by the external medium. We fit the afterglow lightcurve, and extract from this fit some evidence that internal shocks must have occurred previously in the ejecta.