Non-relativistic perpendicular shocks modeling young supernova remnants: nonstationary dynamics and particle acceleration at forward and reverse shocks

TL;DR

This study uses advanced 2D3V particle-in-cell simulations to explore non-relativistic perpendicular shocks in young supernova remnants, revealing nonstationary dynamics, shock rippling, and limited electron acceleration.

Contribution

It introduces an improved simulation setup for modeling shocks with realistic 3D effects and analyzes microphysical processes affecting particle acceleration in supernova remnants.

Findings

Shock rippling occurs on scales set by ion gyro-motions.

A stable suprathermal ion tail is observed, but electrons are not efficiently accelerated.

No turbulent reconnection was detected in the simulations.

Abstract

For parameters that are applicable to the conditions at young supernova remnants, we present results of 2D3V particle-in-cell simulations of a non-relativistic plasma shock with a large-scale perpendicular magnetic field inclined at 45-deg angle to the simulation plane to approximate 3D physics. We developed an improved clean setup that uses the collision of two plasma slabs with different density and velocity, leading to the development of two distinctive shocks and a contact discontinuity. The shock formation is mediated by Weibel-type filamentation instabilities that generate magnetic turbulence. Cyclic reformation is observed in both shocks with similar period, for which we note global variations on account of shock rippling and local variations arising from turbulent current filaments. The shock rippling occurs on spatial and temporal scales given by gyro-motions of shock-reflected ions. The drift motion of electrons and ions is not a gradient drift, but commensurates with E x B drift. We observe a stable suprathermal tail in the ion spectra, but no electron acceleration because the amplitude of Buneman modes in the shock foot is insufficient for trapping relativistic electrons. We see no evidence of turbulent reconnection. A comparison with other 2D simulation results suggests that the plasma beta and the ion-to-electron mass ratio are not decisive for efficient electron acceleration, but pre-acceleration efficacy might be reduced with respect to the 2D results once three-dimensional effects are fully accounted for. Other microphysical factors may also be at play to limit the amplitude of Buneman waves or prevent return of electrons to the foot region.