Properties of time profiles of gamma -ray bursts using pulse decomposition analysis.

摘要

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. I have developed an interactive pulse-fitting program written in IDL using the phenomenological pulse model of Norris, et al., a maximum-likelihood fitting routine, and a semi-automatic routine to determine initial guesses for the fitting routine from time profiles smoothed by a wavelet de-noising algorithm. I 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.;I 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. I carry out simulations to determine the biases that our procedures may introduce. Among the results are that pulses tend to have shorter rise times than decay times, and tend to be narrower and peak earlier at higher energies. I also examine correlations between brightness measures and timescale measures which may result from cosmological time dilation of bursts, or from intrinsic properties of burst sources or from selection effects. The correlations between these parameters among pulses within individual bursts give a measure of the intrinsic effects while the correlations among bursts could result both from intrinsic and cosmological effects. I find that timescales tend to be shorter in bursts with higher peak fluxes, but tend to be longer in bursts with higher total fluences. I also find that peak fluxes and total fluences of bursts are uncorrelated, indicating that they cannot both be good distance indicators for bursts.