Electron acceleration at supernova remnants

TL;DR

This paper reviews recent kinetic simulation studies of supernova remnant shocks, focusing on electron pre-acceleration and heating mechanisms crucial for cosmic ray acceleration.

Contribution

It provides new insights into electron injection processes at SNR shocks through detailed PIC simulations considering various shock parameters.

Findings

Electron heating depends on shock obliquity and Mach number.

Pre-acceleration mechanisms are identified as key to electron injection.

Simulation results inform models of cosmic ray origin.

Abstract

Supernova remnants (SNRs) are believed to produce the majority of galactic cosmic rays (CRs). SNRs harbor non-relativistic collisionless shocks responsible for acceleration of CRs via diffusive shock acceleration (DSA), in which particles gain their energies via repeated interactions with the shock front. As the DSA theory involves pre-existing mildly energetic particles, a means of pre-acceleration is required, especially for electrons. Electron injection remains one of the most troublesome and still unresolved issues and our physical understanding of it is essential to fully comprehend the physics of SNRs. To study any electron-scale phenomena responsible for pre-acceleration, we require a method capable of resolving these small kinetic scales and Particle-in-cell (PIC) simulations fulfill this criterion. Here I report on the latest achievements made by utilising kinetic simulations of non-relativistic high Mach number shocks. I discuss how the physics of SNR shocks depend on the shock parameters (e.g., the shock obliquity, Mach numbers, the ion-to-electron mass ratio) as well as processes responsible for the electron heating and acceleration.