Temporal properties of short GRBs

We analyze a sample of bright short bursts from the BATSE 4B-catalog and find that many short bursts are highly variable (δtmin/T ≪ 1, where δtmin is the shortest pulse duration and T is the burst duration). This indicates that it is unlikely that short bursts are produced by external shocks. We also analyze the available (first 1-2 seconds) high resolution (TTE) data of some of the long bursts. We find that variability on a 10ms time-scale is common in long bursts. This result shows that some long bursts are even more variable than it was thought before (δtmin/T ≈ 10 −4 − 10).