X-ray flares from dense shells formed in gamma-ray burst explosions

TL;DR

This paper proposes a model where dense shells in gamma-ray burst ejecta interact with reverse shocks, naturally explaining the observed features of X-ray flares during early afterglow.

Contribution

It introduces a novel explanation for X-ray flares involving reverse shock interactions with dense shells in the ejecta, accounting for their timing and shape.

Findings

The model reproduces the fast rise and steep decline of X-ray flares.

It explains the characteristic peak duration ratio  t / t= (0.1-0.3).

Provides a natural mechanism for observed flare features.

Abstract

Bright X-ray flares are routinely detected by the Swift satellite during the early afterglow of gamma-ray bursts, when the explosion ejecta drives a blast wave into the external medium. We suggest that the flares are produced as the reverse shock propagates into the tail of the ejecta. The ejecta is expected to contain a few dense shells formed at an earlier stage of the explosion. We show an example of how such dense shells form and describe how the reverse shock interacts with them. A new reflected shock is generated in this interaction, which produces a short-lived X-ray flare. The model provides a natural explanation for the main observed features of the X-ray flares --- the fast rise, the steep power-law decline, and the characteristic peak duration \Delta t /t= (0.1-0.3).