Kinetic simulation of nonrelativistic perpendicular shocks of young supernova remnants. IV. Electron heating

TL;DR

This study uses large-scale Particle-In-Cell simulations to investigate electron heating mechanisms in high Mach number nonrelativistic shocks, revealing the dominant role of shock potential and magnetic instabilities in elevating electron temperatures.

Contribution

It provides a detailed simulation-based analysis of electron heating processes in supernova remnant shocks, highlighting the importance of shock potential and magnetic turbulence.

Findings

Electrons are heated mainly by shock potential.

Magnetic Weibel instability tangles field lines, aiding electron heating.

Predicted ion-electron temperature ratios match observations.

Abstract

High Mach number collisionless shocks are found in planetary systems and supernova remnants (SNRs). Electrons are heated at these shocks to the temperature well above the Rankine-Hugoniot prediction. However processes responsible for electron heating are still not well understood. We use a set of large-scale Particle-In-Cell simulations of non-relativistic shocks in high Mach number regime to clarify the electron heating processes. The physics of these shocks is defined by ion reflection at the shock ramp. Further interaction of the reflected ions and the upstream plasma excites electrostatic Buneman and two-stream ion-ion Weibel instabilities. Electrons are heated via shock surfing acceleration, the shock potential, magnetic reconnection, stochastic Fermi scattering and the shock compression. The main contributor is the shock potential. Magnetic field lines are tangled due to the Weibel instability, which allows the parallel electron heating by the shock potential. The constrained model of the electron heating predicts the ion-to-electron temperature ratio within observed values at SNR shocks and in Saturn's bow shock.