Particle Acceleration in Relativistic Plasma Turbulence

TL;DR

This study uses particle-in-cell simulations to demonstrate that relativistic plasma turbulence naturally produces power-law energy spectra of particles, with characteristics influenced by magnetization and turbulence strength, relevant for astrophysical high-energy sources.

Contribution

It reveals that relativistic turbulence inherently generates nonthermal power-law particle spectra, with spectral slopes and cutoffs independent of system size and dimensionality.

Findings

Power-law spectra are a generic outcome of relativistic turbulence.

Spectral slope becomes system-size independent at large scales.

High-energy cutoff increases linearly with system size.

Abstract

Due to its ubiquitous presence, turbulence is often invoked to explain the origin of nonthermal particles in astrophysical sources of high-energy emission. With particle-in-cell simulations, we study decaying turbulence in magnetically-dominated (or equivalently, "relativistic") pair plasmas. We find that the generation of a power-law particle energy spectrum is a generic by-product of relativistic turbulence. The power-law slope is harder for higher magnetizations and stronger turbulence levels. In large systems, the slope attains an asymptotic, system-size-independent value, while the high-energy spectral cutoff increases linearly with system size; both the slope and the cutoff do not depend on the dimensionality of our domain. By following a large sample of particles, we show that particle injection happens at reconnecting current sheets; the injected particles are then further accelerated by stochastic interactions with turbulent fluctuations. Our results have important implications for the origin of non-thermal particles in high-energy astrophysical sources.