Revealing an unexpectedly low electron injection threshold via reinforced shock acceleration

TL;DR

This paper presents a reinforced shock acceleration model that explains how collisionless shocks can efficiently accelerate electrons to relativistic energies, enhancing understanding of cosmic ray origins.

Contribution

It introduces a new multiscale model incorporating transient structures and wave-particle interactions, revealing a lower electron injection threshold than previously thought.

Findings

Electron injection threshold is in the suprathermal range.

Typical shocks can accelerate electrons to relativistic energies.

The model aligns with satellite measurements and theoretical predictions.

Abstract

Collisionless shock waves, found in supernova remnants, interstellar, stellar, and planetary environments, and laboratories, are one of nature's most powerful particle accelerators. This study combines in situ satellite measurements with recent theoretical developments to establish a reinforced shock acceleration model for relativistic electrons. Our model incorporates transient structures, wave-particle interactions, and variable stellar wind conditions, operating collectively in a multiscale set of processes. We show that the electron injection threshold is on the order of suprathermal range, obtainable through multiple different phenomena abundant in various plasma environments. Our analysis demonstrates that a typical shock can consistently accelerate electrons into very high (relativistic) energy ranges, refining our comprehension of shock acceleration while providing insight on the origin of electron cosmic rays.