GRB minimum variability timescale

We compare these correlations with predictions from recent numerical simulations for a relativistic structured - possibly wobbling - jet and assess the value of temporal variability studies as probes of prompt-emission dissipation physics. We used the peak detection algorithm mepsa to identify the shortest pulse within a GRB time history and preliminarily calibrated mepsa to estimate the full width half maximum (FWHM) duration.

We then applied this framework to two sets of GRBs: Swift GRBs (from 2005 to July 2022) and Insight Hard Modulation X-ray Telescope (Insight-HXMT) GRBs (from June 2017 to July 2021, including the exceptional 221009A). We then selected 401 GRBs with measured redshift to test for correlations. Results.

We confirm that on average short GRBs have significantly shorter MVT than long GRBs. The MVT distribution of short GRBs with extended emission such as 060614 and 211211A is compatible only with that of short GRBs. This is important because it provides a new clue on the progenitor's nature.

The MVT for long GRBs with measured redshift anti-correlates with peak luminosity; our analysis includes careful evaluation of selection effects. We confirm the anti-correlation with the Lorentz factor and find a correlation with the jet opening angle as estimated from the afterglow light curve, along with an inverse correlation with the number of pulses. The MVT can identify the emerging putative new class of long GRBs that are suggested to be produced by compact binary mergers.

For otherwise typical long GRBs, the different correlations between MVT and peak luminosity, Lorentz factor, jet opening angle, and number of pulses can be explained within the context of structured, possibly wobbling, weakly magnetised relativistic jets.