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Session 48 - Gamma Rays & X-ray Instrumentation.
Display session, Thursday, January 08
Exhibit Hall,
Previously, time-dilation studies have been performed in which gamma-ray burst (GRB) time profiles were analyzed for average wavelet amplitude integrated over time, or in which widths of average profiles in peak registration were measured (e.g., Norris et al. 1994, ApJ, 424, 540). Here we investigate average wavelet amplitude as a function of position and timescale, using the 'Mexican Hat' as the orthonormal basis function. The sample consists of more than 825 long GRBs (duration > 2 s) recorded by the Burst and Transient Source Experiment (BATSE). In order to nullify brightness bias, signal-to-noise levels and intensities were equalized for all bursts in the sample. In the time dimension, profiles were peak-aligned, and ranked according to intensity into six brightness groups. We find that the average, peak-aligned wavelet transforms of dim bursts evince greater activity on longer timescales at all times than do bright bursts. We quantify the degree of self-similarity of this time-dilation effect by stretching and redshifting profiles of bright bursts by a factor of two and comparing their average wavelet transforms with those of dimmer burst groups.
