Heating and Acceleration of Intracluster Medium Electrons by Turbulence

TL;DR

This paper examines whether turbulence can accelerate electrons in galaxy cluster media to produce observed X-ray emissions, finding that rapid acceleration heats the plasma and is likely short-lived.

Contribution

It provides a detailed Fokker-Planck analysis of electron acceleration and lifetime issues, highlighting the challenges of sustaining nonthermal electrons in the intracluster medium.

Findings

Nonthermal electron lifetimes are problematic under Coulomb collisions.

Rapid acceleration leads to significant plasma heating.

Nonthermal components only develop with fast acceleration rates.

Abstract

In this paper we investigate the feasibility of bremsstrahlung radiation from `nonthermal' electrons as a source of hard X-rays from the intracluster medium of clusters of galaxies. With an exact treatment of the Coulomb collisions in a Fokker-Planck analysis of the electron distribution we find that the severe difficulties with lifetimes of `nonthermal' particles found earlier by Petrosian (2001) using a cold target model remain problematic. We then address possible acceleration of background electrons into a nonthermal tail. We assume a simplified but generic acceleration rate and determine the expected evolution of an initially Maxwellian distribution of electrons. We find that strong nonthermal components arise only for rapid rate of acceleration which also heats up the entire plasma. These results confirm the conclusion that if the observed `nonthermal' excesses are due to some process accelerating the background thermal electrons this process must be short lived.