Particle transport and heating in the microturbulent precursor of relativistic shocks

TL;DR

This paper explores how microturbulence affects particle transport and heating in relativistic shocks, with implications for particle acceleration and gamma-ray burst emissions.

Contribution

It provides a detailed analysis of particle transport and electron preheating in microturbulent precursors of relativistic shocks, focusing on filamentation and oblique two-stream instabilities.

Findings

Transport of suprathermal particles influences acceleration efficiency.

Electrons experience significant preheating due to microturbulent electric fields.

Maximal synchrotron photon energy estimated at a few GeV.

Abstract

Collisionless relativistic shocks have been the focus of intense theoretical and numerical investigations in recent years. The acceleration of particles, the generation of electromagnetic microturbulence and the building up of a shock front are three interrelated essential ingredients of a relativistic collisionless shock wave. In this paper we investigate two issues of importance in this context: (1) the transport of suprathermal particles in the excited microturbulence upstream of the shock and its consequences regarding particle acceleration; (2) the preheating of incoming background electrons as they cross the shock precursor and experience relativistic oscillations in the microturbulent electric fields. We place emphasis on the importance of the motion of the electromagnetic disturbances relatively to the background plasma and to the shock front. This investigation is carried out for the two major instabilities involved in the precursor of relativistic shocks, the filamentation instability and the oblique two stream instability. Finally, we use our results to discuss the maximal acceleration at the external shock of a gamma-ray burst; we find in particular a maximal synchrotron photon energy of the order of a few GeV.