On the Intrinsic and Cosmological Signatures in Gamma‐Ray Burst Time Profiles: Time Dilation

The time profiles of many gamma-ray bursts consist of distinct pulses, whichoffers the possibility of characterizing the temporal structure of these burstsusing a relatively small set of pulse shape parameters. We have used a pulsedecomposition procedure to analyze the Time-to-Spill (TTS) data for all burstsobserved by BATSE up through trigger number 2000, in all energy channels forwhich TTS data is available. We obtain amplitude, rise and decay timescales, apulse shape parameter, and the fluences of individual pulses in all of thebursts. We investigate the correlations between brightness measures (amplitudeand fluence) and timescale measures (pulse width and separation) which mayresult from cosmological time dilation of bursts, or from intrinsic propertiesof burst sources or from selection effects. The effects of selection biases areevaluated through simulations. The correlations between these parameters amongpulses within individual bursts give a measure of the intrinsic effects whilethe correlations among bursts could result both from intrinsic and cosmologicaleffects. We find that timescales tend to be shorter in bursts with higher peakfluxes, as expected from cosmological time dilation effects, but also find thatthere are non-cosmological effects contributing to this inverse correlation. Wefind that timescales tend to be longer in bursts with higher total fluences,contrary to what is expected from cosmological effects. We also find that peakfluxes and total fluences of bursts are uncorrelated, indicating that theycannot both be good distance indicators for bursts.