Evidence of mini-jet emission in a large emission zone from a magnetically-dominated gamma-ray burst jet

TL;DR

This study analyzes the prompt emission of the exceptionally bright GRB230307A, revealing evidence for mini-jet activity within a large, magnetically-dominated emission zone, consistent with magnetic reconnection models.

Contribution

It provides observational evidence supporting the mini-jet emission scenario in a large GRB jet, linking rapid variability to magnetic reconnection processes.

Findings

Prompt emission consists of many individual mini-jets.

Energy-dependent pulse profiles suggest a common emission site.

Results support magnetic reconnection as the emission mechanism.

Abstract

The second brightest GRB in history, GRB230307A, provides an ideal laboratory to study the mechanism of GRB prompt emission thanks to its extraordinarily high photon statistics and its single episode activity. Here we demonstrate that the rapidly variable components of its prompt emission compose an overall broad single pulse-like profile. Although these individual rapid components are aligned in time across all energy bands, this overall profile conspires to show a well-defined energy-dependent behavior which is typically seen in single GRB pulses. Such a feature demonstrates that the prompt emission of this burst is from many individual emitting units that are casually linked in a emission site at a large distance from the central engine. Such a scenario is in natural consistency with the internal-collision-induced magnetic reconnection and turbulence framework, which invokes many mini-jets due to local magnetic reconnection that constantly appear and disappear in a global magnetically-dominated jet.