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Session 10 - Gamma-ray Bursts and Soft Gamma-ray Repeaters.
Display session, Monday, January 15
North Banquet Hall, Convention Center

[10.01] Search for Time Dilation in Short Gamma-Ray Bursts

J. P. Norris (NASA/GSFC), J. D. Scargle (NASA/ARC), J. T. Bonnell (USRA,GSFC), R. J. Nemiroff (George Mason,GSFC)

We perform a search for time dilation in short (T_90 < 2 s) gamma-ray bursts using the pulse-width and auto-correlation statistics. Both measures avoid the problem of accurate estimation of burst onset and cessation in the presence of relatively large statistical fluctuations in dim bursts. We fit pulses using time-tagged event data (2 \mus resolution). The pulse-fitting algorithm is entirely automatic, employs a Poisson cost function, links information between energy channels, and utilizes the data at original resolution. The latter feature is important since pulses in short bursts can be factors of \sim 10--100 shorter than pulses in long bursts. Peak intensities, also determined in the pulse-fitting process, are converted to peak fluxes using 4-channel detector response matrices. The peak fluxes are used to rank burst brightness. Brightness selection effects are addressed by rendering signal-to-noise levels equal to that of the dimmest bursts in the sample and then exploring the thresholds at which bright and dim bursts drop from the sample. Time-dilation statistics are then generated for surviving bursts grouped by peak flux. We report latest results derived for a sample of \sim 200 short bursts detected by BATSE on the Compton Gamma Ray Observatory.

Program listing for Monday