Properties of Gamma-Ray Burst Time Proles Using Pulse Decomposition Analysis

The time proles of many gamma-ray bursts consist of distinct pulses, which of-fers the possibility of characterizing the temporal structure of these bursts using a relatively small set of pulse shape parameters. This pulse decomposition anal-ysis 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-tting program using the phenomenological pulse model of Norris, et al. and a maximum-likelihood tting 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. We present statistical information on the attributes of pulses comprising these bursts, including relations between pulse characteristics in dierent 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 nd that pulses tend to have shorter rise times than decay times, and tend to be narrower and peak earlier at higher energies. We also nd 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 tends to decrease with time within bursts