Structure of a strong supernova shock wave and rapid electron acceleration confined in its transition region

TL;DR

This paper reports a new rapid electron acceleration process within supernova shock transition regions, revealing complex plasma structures and mechanisms that produce high-energy electrons up to 10 MeV.

Contribution

The study uncovers a novel electron energization mechanism in supernova shocks through numerical simulations, highlighting the role of large-amplitude field structures and hot electrons in acceleration.

Findings

Large-amplitude field structures like wave packets and magnetic humps are generated.

Electrons are accelerated directly via multiple nonlinear scatterings.

Maximum electron energy estimated to reach ~10 MeV within the shock transition region.

Abstract

A new rapid energization process within a supernova shock transition region (STR) is reported by utilizing numerical simulation. Although the scale of a STR as a main dissipation region is only several hundreds of thousands km, several interesting structures are found relating to generation of a root of the energetic particles. The nonlinear evolution of plasma instabilities lead to a dynamical change in the ion phase space distribution which associates with change of the field properties. As a result, different types of large-amplitude field structures appear. One is the leading wave packet and another is a series of magnetic solitary humps. Each field structure has a microscopic scale (~ the ion inertia length). Through the multiple nonlinear scattering between these large-amplitude field structures, electrons are accelerated directly. Within a STR, quick thermalization realizes energy equipartition between the ion and electron, hot electrons play an important role in keeping these large-amplitude field structures on the ion-acoustic mode. The hot electron shows non-Maxwellian distribution and could be the seed of further non-thermal population. The "shock system", where fresh incoming and reflected ions are supplied constantly, play an essential role in our result. With a perpendicular shock geometry, the maximum energy of the electron is estimated by equating a width of the STR to a length of the Larmor radius of the energetic electron. Under some realistic condition of M_A = 170 and \omega_{pe}/\Omega_{ce} = 120, maximum energy is estimated to ~ 10 MeV at an instant only within the STR.