Short Gamma-Ray Bursts Are Different

Abstract

We analyze BATSE time-tagged event (TTE) data for short gamma-ray bursts (T90 duration < 2.6 s), studying spectral lag vs. peak flux and duration, as well as the number of distinct pulse structures per burst. Performing the cross-correlation between two energy bands, we measure an average lag ∼ 20–40 x shorter than for long bursts, and a lag distribution close to symmetric about zero – unlike long bursts. Using a “Bayesian Block” method to identify significantly distinct pulse peaks, we find an order of magnitude fewer pulses than found in studies of long bursts. The disparity in lag magnitude is discontinuous across the ∼ 2-s valley between long and short bursts. Thus, short bursts do not appear to be representable as a continuation of long bursts’ temporal characteristics.