Quiescent times in Gamma-Ray-Bursts: evidence of a dormant inner engine
Abstract
The time structure of Gamma Ray Bursts (GRBs) is usually complex and it often displays several short pulses separated by time intervals lasting from fractions of second to several ten of seconds. A previous statistical analysis has shown that there are three time-scales in the GRB light curves: the shortest one is the variability scale determining the pulses' durations and the intervals between pulses; the largest one describes the total duration of the burst and finally, an intermediate time scale is associated with long periods within the bursts having no activity, the so called quiescent times. Here we show, through a statistical analysis, that if a quiescent time longer than a few ten of seconds is present in the light curve then the pre-quiescence and the post-quiescence emissions have similar variability scales, but the post-quiescence emission is longer and only marginally softer than the pre-quiescence emission. The similarities between the first and the second emission periods strongly suggest that both emissions are produced by the same mechanism and that long quiescent times are generated by a turning off of the inner engine rather than by stochastic modulation of a continuous wind.Keywords
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