PIC simulations of nonrelativistic high-Mach-number oblique shocks propagating in a turbulent medium

TL;DR

This study uses 2D3V PIC simulations to investigate how pre-existing turbulence affects electron acceleration and wave instabilities at non-relativistic oblique shocks in astrophysical environments.

Contribution

First 2D3V PIC simulations examining the impact of upstream turbulence on electron foreshock dynamics and instabilities at non-relativistic oblique shocks.

Findings

Pre-existing turbulence enhances magnetic fluctuations and nonlinear structures.

Turbulence leads to a shorter, hotter electron foreshock.

More numerous and higher-energy non-thermal electrons are produced with turbulence.

Abstract

Collisionless shocks are common in astrophysical systems and stand as sites of particle acceleration. While particles at perpendicular shocks may not return to the upstream region, at oblique shocks a fraction of energetic electrons manage to escape the shock and travel upstream. An extended region known as the electron foreshock is formed, where these reflected particles drive various instabilities that may promote electron acceleration. Here we present the first 2D3V particle-in-cell (PIC) simulations of electron-ion non-relativistic oblique shocks that explore the interaction of the foreshock with pre-existing compressive turbulence with relative amplitude of 15% based on interstellar medium estimates. We find that pre-existing turbulence influences the emergence and behavior of the whistler-wave instability, as it enhances the amplitudes of the magnetic-field fluctuations and leads to larger nonlinear structures. This impacts the dynamics of the reflected electrons, resulting in a shorter and hotter electron foreshock. At the end of our simulations, with pre-existing upstream turbulence we observe non-thermal electrons that are more numerous, reach higher energies, and carry a larger portion of the total energy.