THE AVERAGE INTENSITY AND SPECTRAL EVOLUTION OF BATSE COSMIC GAMMA-RAY BURSTS

Statistical studies of BATSE gamma-ray bursts are presented: we averag e the time profiles, aligning the events at their highest peaks. Using the time histories in different energy channels, we summarize the gen eral features of the average intensity and spectral evolution of gamma -ray bursts (GRBs) and compare the average evolution of bright and dim events. While no differences are found between the average intensity histories, the average hardness ratio histories demonstrate a hardness /brightness correlation. The observed lack of differences between the intensity histories of bright and dim bursts is incompatible with cosm ological time dilation effects predicted by simple cosmological models . The combined results of no intensity history difference but a hardne ss history difference between bright and dim bursts places constraints on galactic models for the origin of GRBs.