Microphysical Plasma Relations from Special-relativistic Turbulence

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 the β parameter. We here present a very comprehensive campaign of two-dimensional kinetic particle-in-cell simulations of special-relativistic turbulence to investigate systematically the microphysical properties of the plasma in the transrelativistic regime. Using a realistic mass ratio between electrons and protons, we analyze how the index of the electron energy distributions κ , 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 β and σ . For each of these quantities, we provide two-dimensional fitting functions that describe their behavior in the relevant space of parameters, thus connecting the microphysical properties of the plasma, κ , ${ \mathcal E }$ , and ${ \mathcal T }$ , with the macrophysical ones β and σ . In this way, our results can find application in a wide range of astrophysical scenarios, including the accretion and the jet emission onto supermassive black holes, such as M87* and Sgr A*.

Keywords

• Plasma astrophysics