Intrinsic and Cosmological Signatures in Gamma-Ray Burst Time Pro les: Time Dilation

The time pro les 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. We have used a pulse decomposition procedure 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 obtain amplitude, rise and decay timescales, a pulse shape parameter, and the uences of individual pulses in all of the bursts. We investigate the correlations between brightness measures (amplitude and uence) and timescale measures (pulse width and separation) which may result from cosmological time dilation of bursts, or from intrinsic properties of burst sources or from selection e ects. The e ects of selection biases are evaluated through simulations. The correlations between these parameters among pulses within individual bursts give a measure of the intrinsic e ects while the correlations among bursts could result both from intrinsic and cosmological e ects. We nd that timescales tend to be shorter in bursts with higher peak uxes, as expected from cosmological time dilation e ects, but also nd that there are non-cosmological e ects contributing to this inverse correlation. We nd that timescales tend to be longer in bursts with higher total uences, contrary to what is expected from cosmological e ects. We also nd that peak uxes and total uences of bursts are uncorrelated, indicating that they cannot both be good distance indicators for bursts. Submitted to Astrophysical Journal Work supported by Department of Energy contract DE{AC03{76SF00515. Intrinsic and Cosmological Signatures in Gamma-Ray Burst Time Pro les: Time Dilation Andrew Lee and Elliott D. Bloom Stanford Linear Accelerator Center, Stanford University, Stanford, California 94309 Vah e Petrosian Center for Space Science and Astrophysics, Varian 302c, Stanford University, Stanford, CA 94305-4060 1