Connection between Pulse Asymmetry and Spectral Softening in Gamma-Ray Bursts

Details Connection between Pulse Asymmetry and Spectral Softening in Gamma-Ray Bursts Connection between Pulse Asymmetry and Spectral Softening in Gamma-Ray Bursts

Dec 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994aas...185.1507n&link_type=abstract

American Astronomical Society, 185th AAS Meeting, #15.07; Bulletin of the American Astronomical Society, Vol. 26, p.1333

Astronomy and Astrophysics

Astronomy

2

Scientific paper

For the purpose of studying the relationship between pulse shape and spectral evolution, we analyzed the time profiles of 45 long (> 1.5 s), bright (> 18000 counts s(-1) ) gamma-ray bursts detected by the Burst And Transient Source Experiment (BATSE) on the Compton Observatory. The data used are recorded with 64-ms resolution, in 4 energy bands ( ~ 25--50, 50--100, 100--300, > 300 keV). Pulses in the time profiles were fitted using a pulse model with rise and decay time constants and a peakedness parameter. On average (with a wide variation), 10 pulses are required to represent a burst profile. Considering only the subset of fitted pulses which do not overlap substantially ( ~ 20% of total), we find that most pulse shapes range from symmetric to fast-rise, slow-decay -- with only a small fraction rising more slowly than they decay. Corresponding to this one-sided range in rise-to-decay ratio is a one-sided range in shift of pulse centroid with energy: the lower the rise-to-decay ratio, the farther the centroid at low energy tends to be shifted to later times relative to the centroid at high energy. Most ``separable" pulses in long bursts have widths in the range 200--600 ms (FWHM); pulse centroids shift ~ 0--300 ms from high (> 300 keV) to low energy (25--50 keV), mostly as a result of pulse narrowing rather than peak shifting, while rise-to-decay ratios decrease from near unity to ~ 0.2.

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