Magnetic fields in cosmic particle acceleration sources

TL;DR

This paper reviews magnetic phenomena in astrophysical particle accelerators, focusing on magnetic field amplification processes driven by cosmic rays in shock environments, and their impact on particle energies and observable emissions.

Contribution

It discusses novel cosmic-ray-driven magnetic field amplification mechanisms and their effects on shock physics and cosmic magnetic field evolution.

Findings

CR-driven magnetic field amplification influences maximum particle energies.

Magnetic fluctuations cause observable synchrotron structures.

CR instabilities generate mesoscale magnetic fields in shock precursors.

Abstract

We review here some magnetic phenomena in astrophysical particle accelerators associated with collisionless shocks in supernova remnants, radio galaxies and clusters of galaxies. A specific feature is that the accelerated particles can play an important role in magnetic field evolution in the objects. We discuss a number of CR-driven, magnetic field amplification processes that are likely to operate when diffusive shock acceleration (DSA) becomes efficient and nonlinear. The turbulent magnetic fields produced by these processes determine the maximum energies of accelerated particles and result in specific features in the observed photon radiation of the sources. Equally important, magnetic field amplification by the CR currents and pressure anisotropies may affect the shocked gas temperatures and compression, both in the shock precursor and in the downstream flow, if the shock is an efficient CR accelerator. Strong fluctuations of the magnetic field on scales above the radiation formation length in the shock vicinity result in intermittent structures observable in synchrotron emission images. Resonant and non-resonant CR streaming instabilities in the shock precursor can generate mesoscale magnetic fields with scale-sizes comparable to supernova remnants and even superbubbles. This opens the possibility that magnetic fields in the earliest galaxies were produced by the first generation Population III supernova remnants and by clustered supernovae in star forming regions.