Origin of intense electron heating in relativistic blast waves

TL;DR

This paper presents a theoretical model explaining intense electron heating in relativistic collisionless shocks, supported by PIC simulations, which is crucial for understanding gamma-ray burst afterglow emissions.

Contribution

It introduces a novel Joule-like heating mechanism driven by pitch-angle scattering and charge-separation fields, validated through large-scale PIC simulations.

Findings

The electric field across the shock precursor is confirmed by PIC simulations.

The proposed model accounts for the majority of electron heating observed.

Simulation results align with the theoretical predictions.

Abstract

The modeling of gamma-ray burst afterglow emission bears witness to strong electron heating in the precursor of Weibel-mediated, relativistic collisionless shock waves propagating in unmagnetized electron-ion plasmas. In this Letter, we propose a theoretical model, which describes electron heating via a Joule-like process caused by pitch-angle scattering in the decelerating, self-induced microturbulence and the coherent charge-separation field induced by the difference in inertia between electrons and ions. The emergence of this electric field across the precursor of electron-ion shocks is confirmed by large-scale particle-in-cell (PIC) simulations. Integrating the model using a Monte Carlo-Poisson method, we compare the main observables to the PIC simulations to conclude that the above mechanism can indeed account for the bulk of electron heating.