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 $\delta t_{min}/T \ll 1$ (where $\delta t_{min}$ 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 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 quiescent times) is similar and correlated with the distribution of the pulses width, in agreement with the predictions of the internal shock model.