Microphysical Plasma Relations from Special-relativistic Turbulence

TL;DR

This study uses 2D kinetic PIC simulations to systematically explore how microphysical plasma properties like electron energy distribution, nonthermal particle efficiency, and temperature ratio depend on macroscopic parameters in relativistic turbulence, aiding astrophysical modeling.

Contribution

It provides comprehensive fitting functions linking microphysical plasma properties with macroscopic parameters in relativistic turbulence, improving modeling of astrophysical plasmas near black holes.

Findings

Electron energy distribution index varies with plasma parameters.

Nonthermal particle production efficiency depends on turbulence conditions.

Electron-to-proton temperature ratio is systematically characterized.

Abstract

The microphysical, kinetic properties of astrophysical plasmas near accreting compact objects are still poorly understood. For instance, in modern general-relativistic magnetohydrodynamic simulations, the relation between the temperature of electrons $T_{e}$ and protons $T_{p}$ is prescribed in terms of simplified phenomenological models where the electron temperature is related to the proton temperature in terms of the ratio between the gas and magnetic pressures, or $\beta$ parameter. We here present a very comprehensive campaign of {two-dimensional} kinetic Particle-In-Cell (PIC) simulations of special-relativistic turbulence to investigate systematically the microphysical properties of the plasma in the trans-relativistic regime. Using a realistic mass ratio between electrons and protons, we analyze how the index of the electron energy distributions $\kappa$, the efficiency of nonthermal particle production $\mathcal{E}$, and the temperature ratio $\mathcal{T}:=T_{e}/T_{p}$, vary over a wide range of values of $\beta$ and $\sigma$. For each of these quantities, we provide two-dimensional fitting functions that describe their behaviour in the relevant space of parameters, thus connecting the microphysical properties of the plasma, $\kappa$, $\mathcal{E}$, and $\mathcal{T}$, with the macrophysical ones $\beta$ and $\sigma$. In this way, our results can find application in wide range of astrophysical scenarios, including the accretion and the jet emission onto supermassive black holes, such as M87* and Sgr A*.