The Energy-Dependence of GRB Minimum Variability Timescales

Understand

We constrain the minimum variability timescales for 938 GRBs observed by the Fermi/GBM instrument prior to July 11, 2012.

• The tightest constraints on progenitor radii derived from these timescales are obtained from light curves in the hardest energy channel.
• In the softer bands -- or from measurements of the same GRBs in the hard X-rays from Swift -- we show that variability timescales tend to be a factor 2--3 longer.
• Applying a survival analysis to account for detections and upper limits, we find median minimum timescale in the rest frame for long-duration and short-duration GRBs of 45 ms and 10 ms, respectively.