Gamma-ray bursts: temporal scales and the bulk lorentz factor

Abstract

For a sample of Swift and Fermi gamma-ray bursts, we show that the minimum variability timescale and the spectral lag of the prompt emission is related to the bulk Lorentz factor in a complex manner. For small Gamma's, the variability timescale exhibits a shallow (plateau) region. For large Gamma's, the variability timescale declines steeply as a function of Gamma (delta T proportional to Gamma(-4.05 +/- 0.64)). Evidence is also presented for an intriguing correlation between the peak times, t(p), of the afterglow emission and the prompt emission variability timescale.