System-size Convergence of Nonthermal Particle Acceleration in Relativistic Plasma Turbulence

Author
Abstract
<p>We apply collisionless particle-in-cell simulations of relativistic pair plasmas to explore whether driven turbulence is a viable high-energy astrophysical particle accelerator. We characterize nonthermal particle distributions for varying system sizes up to\&nbsp;L/2πρ<sub>e0</sub>\&nbsp;=\&nbsp;163, where\&nbsp;L/2π\&nbsp;is the driving scale and\&nbsp;ρ<sub>e0</sub>\&nbsp;is the initial characteristic Larmor radius. We show that turbulent particle acceleration produces power-law energy distributions that, when compared at a fixed number of large-scale dynamical times, slowly steepen with increasing system size. We demonstrate, however, that convergence is obtained by comparing the distributions at different times that increase with system size (approximately logarithmically). We suggest that the system-size dependence arises from the time required for particles to reach the highest accessible energies via Fermi acceleration. The converged power-law index of the energy distribution,\&nbsp;α\&nbsp;≈\&nbsp;3.0 for magnetization\&nbsp;σ\&nbsp;=\&nbsp;3/8, makes turbulence a possible explanation for nonthermal spectra observed in systems such as the Crab Nebula.</p>
Year of Publication
2018
Journal
The Astrophysical Journal
Volume
867
Date Published
2018-10
URL
http://iopscience.iop.org/article/10.3847/2041-8213/aae88c/meta
DOI
10.3847/2041-8213/aae88c
JILA PI
Journal Article