Quiescent times in gamma-ray bursts: II. Dormant periods in the central   engine?
  Within the framework of the internal-external shocks model for gamma-ray bursts, 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 prompt gamma-ray and X-ray emission can in principle determine whether the quiescent episodes are due to a modulated relativistic wind or a switching off of the central engine. 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. 
Enrico Ramirez-Ruiz, Andrea Merloni, Martin J. Rees (IoA, Cambridge)