SIMBAD references

We perform a statistical analysis of the temporal structure of long gamma-ray bursts (GRBs). We consider a sample of bursts in which a long quiescent time is present. By comparing the prequiescent with the postquiescent emission we show that they display similar temporal structures, hardness ratios, and emitted powers, but, on average, the postquiescent emission is roughly twice as long as the prequiescent emission. We then analyze a sample of long and bright GRBs (long and faint GRBs are not included) and find that the average duration of the quiescent times is comparable to the average duration of the emission periods. This leads us to suggest an interpretation of quiescent times as due to dormancy periods of the inner engine. The interpretation of quiescent times as instead caused by stochastic modulations of a continuous wind is less plausible due to the larger energy requirements that it imposes on the inner engine. Interestingly, before and after a dormancy period the inner engine produces similar emissions.