Three-dimensional kinetic simulations of relativistic magnetostatic equilibria

TL;DR

This study uses 3D kinetic simulations to explore how relativistic magnetized pair plasmas relax through magnetic reconnection, producing non-thermal particles and rapid energy release relevant to astrophysical phenomena like blazar flares.

Contribution

It introduces a detailed kinetic simulation of ABC magnetic equilibria, revealing new mechanisms of magnetic dissipation and particle acceleration under radiative losses.

Findings

Magnetic relaxation involves localized collapses and mergers of current layers.

Power-law particle energy distributions up to index -2.3 are produced.

A significant fraction of magnetic energy is converted into radiation.

Abstract

We present the results of three-dimensional kinetic particle-in-cell (PIC) simulations of isotropic periodic relativistically magnetized pair-plasma equilibria known as the ABC fields. We performed several simulations for initial wavenumbers k_ini = 2 or k_ini = 4, different efficiencies of radiative cooling (including radiation reaction from synchrotron and inverse Compton processes), and different mean magnetization values. These equilibria evolve by means of ideal coalescence instability, the saturation of which generates ab initio localized kinetically-thin current layers -- sites of magnetic reconnection and non-thermal particle acceleration -- eventually relaxing to a state of lower magnetic energy at conserved total magnetic helicity. We demonstrate that magnetic relaxation involves in addition localized collapses of magnetic minima and bulk mergers of current layer pairs, which represents a novel scenario of spontaneous magnetic dissipation with application to the rapid gamma-ray flares of blazars and of the Crab Nebula. Particle acceleration under strong radiative losses leads to formation of power-law indices N(gamma) ~ gamma^(-p) up to p ~= -2.3 at mean hot magnetization values of <sigma_hot> ~ 6. Individual energetic particles can be accelerated within one light-crossing time by electric fields that are largely perpendicular to the local magnetic fields. The energetic particles are highly anisotropic due to the kinetic beaming effect, implying complex patterns of rapid variability. A significant fraction of the initial total energy can be radiated away in the overall process of magnetoluminescence.