A STRETCHED EXPONENTIAL LAW FOR THE AVERAGE TIME HISTORY OF GAMMA-RAY BURSTS AND THEIR TIME DILATIONS

摘要

Individual gamma-ray bursts (GRBs) have very diverse time behavior—from a single pulse to a long complex sequence of chaotic pulses of different timescales. I studied time profiles of GRBs using data from the Compton Gamma Ray Observatory's Burst and Transient Source Experiment (BATSE) and found that the postpeak slope of the average peak-aligned time profile of GRBs obeys a unique and simple analytical law, I ～ exp [-(t/t_0)~(1/3)], where t is the time measured from the peak of the event and t_0 is a constant ranging from 0.3 s for strong bursts to ～1 s for weak bursts. The average peak-aligned time profile follows this law with good accuracy in the whole time range available for analysis (from fractions of a second to ～120 s after the peak). Such a law (a stretched exponential) appears in processes associated with fractals (e.g., turbulence). The same analysis for solar flares gives a different shape for the average time profile. The dependence of t_0 on the brightness of GRBs is presented. The time dilation of the dimmest GRBs relative to the brightest GRBs is at least a factor ～2 and possibly ～3. The statistics (600 GRBs), however, still does not allow us to rule out an intrinsic anticorrelation between intensity and duration of GRBs as a possible explanation of the effect. Probably, it is possible to confirm (or disprove) the cosmological origin of GRBs using the total existing statistics of strong bursts.