Time-scales in long gamma-ray bursts

We analyse a sample of bright long bursts and find that the pulse durations have a lognormal distribution while the intervals between pulses have an excess of long intervals (relative to lognormal distribution). This excess can be explained by the existence of quiescent times , long periods with no signal above the background level. The lognormal distribution of the intervals (excluding the quiescent times ) is similar to the distribution of the pulse widths. This result suggests that the quiescent times are made by a different mechanism than the rest of the intervals. It also suggests that the intervals (excluding the quiescent times ) and the pulse width are connected to the same parameters of the source. We find that there is a correlation between a pulse width and the duration of the interval preceding it. There is a weaker, but still a significant, correlation between a pulse width and the interval following it. The significance of the correlation drops substantially when the intervals considered are not adjacent to the pulse.     

Temporal properties of short gamma-ray bursts

We analyse a sample of bright short bursts from the BATSE 4B-catalog and find that many short bursts are highly variable  ( δt _min/ T ≪1  , where δt _min 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 analyse the available (first  1–2 s)  high-resolution Time Tagged Events (TTE) data of some of the long bursts. We find that variability on a 10-ms time-scale is common in long bursts. This result shows that some long bursts are even more variable than it was thought before  ( δt _min/ T ≈10^-4–10^-3)  .