Diffusive shock acceleration at oblique high Mach number shocks

TL;DR

This study investigates the potential for diffusive shock acceleration at oblique high Mach number shocks using PIC and PIC-MHD simulations, revealing that high Mach numbers favor the initiation of cosmic ray acceleration.

Contribution

It demonstrates that diffusive shock acceleration is more likely to occur at high Mach number oblique shocks, highlighting the importance of the Alfvenic Mach number in this process.

Findings

DSA is more feasible at high Mach number shocks.

Reflected particles can generate upstream turbulence.

The process depends strongly on the Alfvenic Mach number.

Abstract

The current paradigm of cosmic ray (CR) origin states that the most part of galactic CRs is produced by supernova remnants. The interaction of supernova ejecta with the interstellar medium after supernova's explosions results in shocks responsible for CR acceleration via diffusive shock acceleration (DSA). We use particle-in-cell (PIC) simulations and a combined PIC-magnetohydrodynamic (PIC-MHD) technique to investigate whether DSA can occur in oblique high Mach number shocks. Using the PIC method, we follow the formation of the shock and determine the fraction of the particles that gets involved in DSA. Then, with this result, we use PIC-MHD simulations to model the large-scale structure of the plasma and the magnetic field surrounding the shock and find out whether or not the reflected particles can generate the upstream turbulence and trigger DSA. We find that the feasibility of this process in oblique shocks depends strongly on the Alfvenic Mach number, and the DSA process is more likely triggered at high Mach number shocks.