Kinetic Simulations of Instabilities and Particle Acceleration in Cylindrical Magnetized Relativistic Jets

TL;DR

This study uses 3D kinetic simulations to explore how instabilities develop and lead to particle acceleration in cylindrical relativistic jets with magnetic fields, revealing the roles of different forces and modes.

Contribution

It extends previous models by analyzing a range of initial jet structures and identifying the limited role of parallel electric fields in particle acceleration.

Findings

Kink mode develops in the jet core with growth rates matching MHD predictions.

Electric fields parallel to magnetic fields play a minor role in acceleration.

Pressure-driven modes are significant in regions with sufficient gas pressure.

Abstract

Relativistic magnetized jets, such as those from AGN, GRBs and XRBs, are susceptible to current- and pressure-driven MHD instabilities that can lead to particle acceleration and non-thermal radiation. Here we investigate the development of these instabilities through 3D kinetic simulations of cylindrically symmetric equilibria involving toroidal magnetic fields with electron-positron pair plasma. Generalizing recent treatments by Alves et al. (2018) and Davelaar et al. (2020), we consider a range of initial structures in which the force due to toroidal magnetic field is balanced by a combination of forces due to axial magnetic field and gas pressure. We argue that the particle energy limit identified by Alves et al. (2018) is due to the finite duration of the fast magnetic dissipation phase. We find a rather minor role of electric fields parallel to the local magnetic fields in particle acceleration. In all investigated cases a kink mode arises in the central core region with a growth timescale consistent with the predictions of linearized MHD models. In the case of a gas-pressure-balanced (Z-pinch) profile, we identify a weak local pinch mode well outside the jet core. We argue that pressure-driven modes are important for relativistic jets, in regions where sufficient gas pressure is produced by other dissipation mechanisms.