Counterpart-Induced Millisecond-Scale Truncation Mechanism of Fast Radio Bursts

TL;DR

This paper proposes a universal physical mechanism involving electron-positron pair cascades that can truncate fast radio bursts to millisecond durations, independent of their origin.

Contribution

It introduces a new physical process explaining FRB millisecond durations, linking gamma-ray counterparts to pair cascades that limit burst length regardless of production origin.

Findings

Pair cascades can truncate FRBs to millisecond durations.

The mechanism is independent of FRB production processes.

Establishes upper bounds on FRB durations based on physical processes.

Abstract

The observed millisecond-scale duration is an essential yet mysterious feature of fast radio bursts (FRBs). In this Letter, we link the observed soft gamma-ray counterpart of FRB 200428 to electron-positron pair cascades driven by Compton scattering and the Breit-Wheeler process. We demonstrate that such pair cascades can truncate FRBs to durations down to millisecond-scale, thereby establishing millisecond-scale upper bounds on their durations. The physical processes involved in the truncation mechanism occur during the propagation of FRBs after their production. Consequently, this mechanism is independent of the specific production mechanism or origin of the FRBs, suggesting that it could potentially operate in all FRBs. Our results lift the constraint on FRB production mechanisms that they must inherently generate bursts lasting only milliseconds.