Simulation of relativistic shocks and associated radiation

TL;DR

This paper presents a new 3-D relativistic electromagnetic particle simulation code to study particle acceleration and radiation in relativistic shocks, revealing electromagnetic field generation and emission spectra consistent with turbulent magnetic fields.

Contribution

Development of a novel 3-D REMP code enabling long-term simulations of relativistic shocks and particle acceleration, including radiation calculations in unmagnetized plasmas.

Findings

Ambient electrons are accelerated and density increases threefold in pair plasmas.

Strong electromagnetic fields are generated behind the bow shock.

Simulated emission spectra match those from turbulent magnetic fields.

Abstract

Using our new 3-D relativistic electromagnetic particle (REMP) code parallelized with MPI, we investigated long-term particle acceleration associated with a relativistic electron-positron jet propagating in an unmagnetized ambient electron-positron plasma. We have also performed simulations with electron-ion jets. The simulations were performed using a much longer simulation system than our previous simulations in order to investigate the full nonlinear stage of the Weibel instability for electron-positron jets and its particle acceleration mechanism. Cold jet electrons are thermalized and ambient electrons are accelerated in the resulting shocks for both cases. Acceleration of ambient electrons leads to a maximum ambient electron density three times larger than the original value for pair plasmas. Behind the bow shock in the jet shock strong electromagnetic fields are generated. These fields may lead to time dependent afterglow emission. We calculated radiation from electrons propagating in a uniform parallel magnetic field to verify the technique. We also used the new technique to calculate emission from electrons based on simulations with a small system with two different cases for Lorentz factors (15 and 100). We obtained spectra which are consistent with those generated from electrons propagating in turbulent magnetic fields with red noise. This turbulent magnetic field is similar to the magnetic field generated at an early nonlinear stage of the Weibel instability.