Convective Instability of a Relativistic Ejecta Decelerated by a Surrounding Medium: An Origin of Magnetic Fields in GRBs?

TL;DR

This study performs a linear stability analysis of relativistic ejecta deceleration, revealing convective instabilities that could influence early gamma-ray burst afterglows and generate magnetic fields in the surrounding medium.

Contribution

It identifies convective Rayleigh-Taylor instability in relativistic ejecta deceleration, suggesting a mechanism for magnetic field generation in GRBs.

Findings

Convective Rayleigh-Taylor instability occurs in the system.

Instability growth is fastest at the contact interface.

Oscillations may influence early afterglow emission and magnetic field origin.

Abstract

Global linear stability analysis of a self-similar solution describing a relativistic shell decelerated by an ambient medium is performed. The system is shown to be subject to the convective Rayleigh-Taylor instability, with a rapid growth of eigenmodes having angular scale much smaller than the causality scale. The growth rate appears to be largest at the interface separating the shocked ejecta and shocked ambient gas. The disturbances produced at the contact interface propagate in the shocked media and cause nonlinear oscillations of the forward and reverse shock fronts. It is speculated that such oscillations may affect the emission from the shocked ejecta in the early afterglow phase of GRBs, and may be the origin of the magnetic field in the shocked circum-burst medium.