Filamentation of the electromagnetic precursor in relativistic quasi-perpendicular electron-positron shocks

TL;DR

This paper investigates how electromagnetic precursor filamentation in relativistic electron-positron shocks can lead to magnetic reconnection and particle acceleration, providing insights into phenomena like pulsar wind nebulae termination shocks.

Contribution

It introduces a novel scenario explaining non-thermal particle acceleration via filamentation instability and magnetic field restructuring in relativistic shocks.

Findings

Filamentation breaks the precursor into radiation filaments of a few plasma skin depths.

Velocity gradients in filaments generate a magnetic field component parallel to the shock normal.

Magnetic reconnection could be triggered upstream, aiding particle acceleration.

Abstract

We present a scenario that could explain non-thermal particle acceleration in relativistic quasi-perpendicular electron-positron shocks, such as the termination shock of pulsar wind nebulae. The shock produces a strong electromagnetic precursor that propagates into the upstream plasma, which is initially threaded by a uniform background magnetic field. We show that the filamentation instability breaks the precursor into radiation filaments parallel to the shock normal. The transverse scale of the filaments is of the order of a few plasma skin depths. In the shock frame, the bulk Lorentz factor of the upstream plasma is significantly reduced inside the radiation filaments. Then, the instability produces a relativistic shear flow with strong velocity gradients on kinetic scales. The velocity gradients distort the background magnetic field lines, and generate a magnetic field component parallel to the shock normal that reverses across each radiation filament, a configuration that could trigger magnetic reconnection in the upstream plasma. These effects may accelerate particles before the plasma enters the shock.