Particle acceleration and pitch-angle evolution in relativistic turbulence

TL;DR

This paper investigates how relativistic turbulence influences the pitch angle distributions of energetic electrons, which are vital for interpreting synchrotron radiation spectra in astrophysical objects, using detailed numerical simulations.

Contribution

It provides a detailed case study of pitch angle distributions during turbulent acceleration, addressing numerical challenges and confirming phenomenological models.

Findings

Numerical noise significantly affects pitch angle scattering.

Techniques are demonstrated to overcome numerical challenges in small pitch angle evolution.

Results align with existing phenomenological models.

Abstract

Synchrotron radiation detected from relativistic astrophysical objects such as pulsar-wind nebulae and {jets from active galactic nuclei} depends on the magnetic fields and the distribution functions of energetic electrons in these systems. Relativistic magnetically dominated turbulence has been recognized as an efficient mechanism for structure formation and non-thermal particle acceleration in these environments. Recent numerical simulations of relativistic turbulence have provided insights into the energy distribution functions of accelerated electrons. Much less is currently understood about their {pitch angle distributions}, which are crucial for accurately interpreting the spectra of synchrotron radiation. {We perform a detailed case study of} the pitch angle distributions formed during the process of turbulent acceleration {for $B_0/\delta B_0 = 10$ and $\tilde{\sigma}_0 \sim 40$, where $B_0$ is the uniform component of the magnetic field, $\delta B_0$ is the fluctuating component, and $\tilde{\sigma}_0$ is the plasma magnetization based on the magnetic fluctuations. We find that even minimal numerical noise can cause substantial pitch angle scattering, but we demonstrate techniques for overcoming the numerical challenges associated with the evolution of very small pitch angles. Our numerical results are consistent with the phenomenological model found in \cite[][]{vega2024b,vega2025}.}