The study of Gamma-ray bursts
(GRBs) has undergone a revolution since the
the first fading sources (afterglows) at X-ray , optical and radio wavelengths were discovered, making
them the most powerful photon-emitters known in the Universe. Although much attention has been devoted to the late afterglow emission since then, the prompt Gamma-ray emission still has to be understood. Many issues remain unsolved, regarding the nature of the central engine, the different scenarios giving rise to this prompt emission, and the radiation mechanisms.
Gamma-ray bursts are so complicated and diverse in the time domain that, at first sight, their behaviour
obeys no simple rule: many bursts have a highly variable temporal profile with a variability time scale that is significantly shorter than the overall duration, while in a minority of them there is only one peak, with no
Results: quiescent times in Gamma-ray bursts
Long GRBs often show multiple episodes of emission, separated by background
intervals of variable duration or quiescent times. In other words,
the emission seems to turn off to a very low level and then turn
This observed property can provide an interesting clue to the nature of Gamma-ray bursts. At present, it
is unclear if these separated emission episodes are consequence of the same physical process (e.g. internal or external shocks), and if the time separation is due to some intrinsic property of the central source or
of its environment. We have investigated this issue in a recent paper (Ramirez-Ruiz & Merloni 2000), and we are currently involved in the preparation of an accompanying paper (Ramirez-Ruiz, Merloni & Rees 2000), in which we will present the implications of quiescent times for different scenarios for the origin of Gamma-ray bursts.