New results on the temporal structure of GRBs

Abstract

We analyze the temporal structure of long ((T_{90}>2sec)) and short ((T_{90}<2sec)) BATSE bursts. We find that: (i) In many short bursts (δt_{min}/T\ll 1) (where (δt_{min}) is the shortest pulse). This indicates that short bursts arise, like long ones, in internal shocks. (ii) In long bursts there is an excess of long intervals between pulses (relative to a lognormal distribution). This excess can be explained by the existence of \emph{quiescent times}, long periods with no signal above the background that arise, most likely, from periods with no source activity. The lognormal distribution of the intervals (excluding the \emph{quiescent times}) is similar and correlated with the distribution of the pulses width, in agreement with the predictions of the internal shock model.