Properties of gamma-ray burst time profiles using pulse decomposition analysis

The time profiles of many gamma-ray bursts consist of distinct pulses, which offers the possibility of characterizing the temporal structure of these bursts using a. relatively small set of pulse shape parameters. This pulse decomposition analysis has previously been performed on a small sample of bright, long bursts using binned data from BATSE, which comes in several data types, and on a sample of short bursts using the BATSE time-tagged event (TTE) data type. We have developed an interactive pulse-fitting program using the phenomenological pulse model of Norris et al. and a maximum-likelihood fitting routine. We have used this program to analyze the time-to-spill (TTS) data for all bursts observed by BATSE up through trigger number 2000, in all energy channels for which TTS data is available. This represents a total of 211 distinct bursts analyzed in one or more energy channels. We present statistical information on the attributes of pulses comprising these bursts, including relations between pulse characteristics in different energy channels and the evolution of pulse characteristics through the course of a burst. We carry out simulations to determine the biases that our procedures may introduce. We find that pulses tend to have shorter rise times than decay times, and tend to be narrower and peak earlier at higher energies. We also find that pulse brightness, pulse width, and pulse hardness ratios do not evolve monotonically within bursts, but that the ratios of pulse rise times to decay times tend to decrease with time within bursts.