Spectral Hardness Decay with Respect to Fluence in BATSE Gamma‐Ray Bursts

We have analyzed the evolution of the spectral hardness parameter Epk as afunction of fluence in gamma-ray bursts. We fit 41 pulses within 26 bursts withthe trend reported by Liang & Kargatis (1996) which found that Epk decaysexponentially with respect to photon fluence. We also fit these pulses with aslight modification of this trend, where Epk decays linearly with energyfluence. In both cases, we found the set of 41 pulses to be consistent with thetrend. For the latter trend, which we believe to be more physical, thedistribution of the decay constant is roughly log-normal, with a mean of 1.75+/- 0.07 and a FWHM of 1.0 +/- 0.1. Regarding an earlier reported invariance inthe decay constant among different pulses in a single burst, we foundprobabilities of 0.49 to 0.84 (depending on the test used) that such invariancewould occur by coincidence, most likely due to the narrow distribution of decayconstant values among pulses.Comment: 17 pages, 7 figure pages, 2 table pages, submitted to The Astrophysical Journa