Abstract

Within the framework of the internal-external shocks model for $\gamma$-ray bursts (GRBs) we study the various mechanisms that can give rise to  quiescent times in the observed $\gamma$-ray light-curves.
In particular, we look for the signatures that can provide us with evidence as to whether
or not the central engine goes dormant for a period of time comparable to the
duration of the gaps.
We show that the properties of the $\gamma$-ray, X-ray and, in particular, optical afterglow determine whether the quiescent episodes are due  to a modulated relativistic wind or a switching-off central engine.
In particular, we suggest that detailed observations of the prompt  afterglow emission from the reverse shock will strongly constrain the possible mechanisms for the production of quiescent times in gamma ray bursts.