SPECTRAL HARDNESS DECAY WITH RESPECT TO FLUENCE IN BATSE GAMMA-RAY BURSTS

摘要

We have analyzed the evolution of the spectral hardness parameter Epk (the maximum of the vFv spectrum) as a function of fluence in gamma-ray bursts. We fit 41 pulses within 26 bursts with the trend reported by Liang di Kargatis, which found that Epk decays exponentially with respect to photon fluence . We also fit these pulses with a slight modification of this trend, where Epk decays lineariy with energy fluence. In both cases, we found the set of 41 pulses to be consistent with the trend. For the latter trend, which we believe to be more physical, the distribution of the decay constant Qo is roughly lognor- mal, where the mean of log-10 Qo is 1.75 ± 0.07 and the FWHM of log_10, Qo is l.0 ± 0.l. Regarding an earlier reported invariance in Qo among different pulses in a single burst, we found probabilities of 0.49- 0,84 (depending on the test used) that such invariance would occur by coincidence, most likely because of the narrow distribution of Qo values among pulses.