On magnetic field amplification and particle acceleration near non-relativistic astrophysical shocks: Particles in MHD Cells simulations

TL;DR

This paper introduces a hybrid simulation approach combining MHD and particle-in-cell techniques to study magnetic field amplification and particle acceleration near non-relativistic astrophysical shocks, revealing new acceleration mechanisms especially in oblique magnetic fields.

Contribution

The study develops a novel hybrid simulation method that captures shock-particle interactions on larger scales, demonstrating magnetic field amplification and particle acceleration in oblique shocks beyond previous models.

Findings

Magnetic field amplification occurs in both parallel and oblique shocks.

Particle acceleration is facilitated by shock front corrugation and upstream entry.

Oblique shocks show acceleration and amplification on longer timescales.

Abstract

We present simulations of magnetized astrophysical shocks taking into account the interplay between the thermal plasma of the shock and supra-thermal particles. Such interaction is depicted by combining a grid-based magneto-hydrodynamics description of the thermal fluid with particle in cell techniques devoted to the dynamics of supra-thermal particles. This approach, which incorporates the use of adaptive mesh refinement features, is potentially a key to simulate astrophysical systems on spatial scales that are beyond the reach of pure particle-in-cell simulations. We consider in this study non-relativistic shocks with various Alfvenic Mach numbers and magnetic field obliquity. We recover all the features of both magnetic field amplification and particle acceleration from previous studies when the magnetic field is parallel to the normal to the shock. In contrast with previous particle-in-cell-hybrid simulations, we find that particle acceleration and magnetic field amplification also occur when the magnetic field is oblique to the normal to the shock but on larger timescales than in the parallel case. We show that in our simulations, the supra-thermal particles are experiencing acceleration thanks to a pre-heating process of the particle similar to a shock drift acceleration leading to the corrugation of the shock front. Such oscillations of the shock front and the magnetic field locally help the particles to enter the upstream region and to initiate a non-resonant streaming instability and finally to induce diffuse particle acceleration.