Preferential Positron Acceleration in Relativistic Magnetized Electron-Positron-Ion Shocks

TL;DR

This paper demonstrates that in relativistic magnetized shocks, positrons are preferentially accelerated via wakefield interactions, with implications for understanding high-energy positron excesses in astrophysical phenomena.

Contribution

It introduces a new mechanism for selective positron acceleration in relativistic shocks using particle-in-cell simulations and theoretical analysis.

Findings

Positrons are preferentially accelerated in magnetized relativistic shocks.

Wakefield interactions are key to the selective acceleration process.

The mechanism explains high-energy positron excesses in pulsar winds.

Abstract

Relativistic shocks are considered efficient accelerators of charged particles and play crucial roles in high-energy astrophysical phenomena, such as gamma-ray bursts and pulsar winds. This study focuses on positron accelerations in magnetized relativistic shocks in electron-positron-ion plasma. Employing one-dimensional ab initio particle-in-cell simulations, we found a preferential positron acceleration through an interaction with the wakefield associated with a precursor wave in the upstream region. Test particle simulations revealed that the selective acceleration occurs for sufficiently large amplitudes of the wakefield. The mechanism can be understood as the relativistic $\boldsymbol{E}\times\boldsymbol{B}$ acceleration formulated in the upstream frame. A theoretical analysis of the positron acceleration in astrophysical contexts is presented, supporting ultra-relativistic shocks in pulsar winds as a primary source for the high-energy positron excess.