Acceleration of Solar Energetic Particles by the shock of Interplanetary Coronal Mass Ejection

TL;DR

This study uses advanced simulations to explore how different types of interplanetary shocks accelerate solar energetic particles, revealing the roles of diffusive shock acceleration and shock drift acceleration depending on shock orientation.

Contribution

The paper introduces MHD-PIC simulations to analyze particle acceleration mechanisms in ICME shocks with varying magnetic orientations and Mach numbers.

Findings

Parallel shocks primarily accelerate particles via DSA.

Quasi-perpendicular shocks mainly use SDA for acceleration.

Higher Mach number shocks accelerate particles more efficiently.

Abstract

Interplanetary Coronal Mass Ejection (ICME) shocks are known to accelerate particles and contribute significantly to Solar Energetic Particle (SEP) events. We have performed Magnetohydrodynamic-Particle in Cell (MHD-PIC) simulations of ICME shocks to understand the acceleration mechanism. These shocks vary in Alfv\'enic Mach numbers as well as in magnetic field orientations (parallel \& quasi-perpendicular). We find that Diffusive Shock Acceleration (DSA) plays a significant role in accelerating particles in a parallel ICME shock. In contrast, Shock Drift Acceleration (SDA) plays a pivotal role in a quasi-perpendicular shock. High-Mach shocks are seen to accelerate particles more efficiently. Our simulations suggest that background turbulence and local particle velocity distribution around the shock can indirectly hint at the acceleration mechanism. Our results also point towards a few possible \textit{in situ} observations that could validate our understanding of the topic.