Test particles in relativistic resistive magnetohydrodynamics

TL;DR

This paper introduces a novel method for evolving charged test particles in resistive relativistic magnetohydrodynamics simulations, analyzing their acceleration and energy distribution in magnetic reconnection scenarios relevant to black hole environments.

Contribution

It is the first to analyze charged test particle evolution within resistive relativistic MHD simulations, providing insights into particle acceleration mechanisms in reconnection layers.

Findings

Electrons accelerate to non-thermal energies in current sheets.

Two acceleration regimes identified: exponential during island coalescence and nonlinear with high variability.

Particle energy distributions depend on Lundquist number, magnetization, and plasma-$eta$.

Abstract

The Black Hole Accretion Code (BHAC) has recently been extended with the ability to evolve charged test particles according to the Lorentz force within resistive relativistic magnetohydrodynamics simulations. We apply this method to evolve particles in a reconnecting current sheet that forms due to the coalescence of two magnetic flux tubes in 2D Minkowski spacetime. This is the first analysis of charged test particle evolution in resistive relativistic magnetohydrodynamics simulations. The energy distributions of an ensemble of 100.000 electrons are analyzed, as well as the acceleration of particles in the plasmoids that form in the reconnection layer. The effect of the Lundquist number, magnetization, and plasma-$\beta$ on the particle energy distribution is explored for a range of astrophysically relevant parameters. We find that electrons accelerate to non-thermal energies in the thin current sheets in all cases. We find two separate acceleration regimes: An exponential increase of the Lorentz factor during the island coalescence where the acceleration depends linearly on the resistivity and a nonlinear phase with high variability. These results are relevant for determining energy distributions and acceleration sites obtaining radiation maps in large-scale magnetohydrodynamics simulations of black hole accretion disks and jets.