Electron acceleration in non-relativistic quasi-perpendicular collisionless shocks

TL;DR

This study uses PIC simulations to analyze how electrons are accelerated in non-relativistic quasi-perpendicular shocks, revealing mechanisms like shock drift acceleration and wave interactions that produce power-law spectra.

Contribution

It demonstrates that high Mach number quasi-perpendicular shocks can efficiently accelerate electrons to nonthermal energies, highlighting the role of magnetic mirroring and wave-driven processes.

Findings

Electrons form power-law spectra consistent with DSA predictions.

Reflected electrons undergo multiple shock drift acceleration cycles.

Proton pre-acceleration occurs due to current-driven upstream waves.

Abstract

We study diffusive shock acceleration (DSA) of electrons in non-relativistic quasi-perpendicular shocks using self-consistent one-dimensional particle-in-cell (PIC) simulations. By exploring the parameter space of sonic and Alfv\'{e}nic Mach numbers we find that high Mach number quasi-perpendicular shocks can efficiently accelerate electrons to power-law downstream spectra with slopes consistent with DSA prediction. Electrons are reflected by magnetic mirroring at the shock and drive non-resonant waves in the upstream. Reflected electrons are trapped between the shock front and upstream waves and undergo multiple cycles of shock drift acceleration before the injection into DSA. Strong current-driven waves also temporarily change the shock obliquity and cause mild proton pre-acceleration even in quasi-perpendicular shocks, which otherwise do not accelerate protons. These results can be used to understand nonthermal emission in supernova remnants and intracluster medium in galaxy clusters.