Collisionless shocks in partly ionized plasma with cosmic rays: microphysics of non-thermal components

TL;DR

This review explores the microphysics of collisionless shocks in partly ionized plasma with cosmic rays, focusing on particle acceleration, magnetic field changes, and observable emission features in astrophysical contexts like supernova remnants.

Contribution

It provides a comprehensive overview of the observational and theoretical understanding of non-thermal components in astrophysical collisionless shocks, emphasizing shock precursors and emission diagnostics.

Findings

Models predict observable emission features revealing shock precursor physics.

Cosmic ray acceleration significantly modifies shock structure and emission spectra.

Recent gamma-ray observations support the role of shocks in cosmic ray production.

Abstract

In this review we discuss some observational aspects and theoretical models of astrophysical collisionless shocks in partly ionized plasma with the presence of non-thermal components. A specific feature of fast strong collisionless shocks is their ability to accelerate energetic particles that can modify the shock upstream flow and form the shock precursors. We discuss the effects of energetic particle acceleration and associated magnetic field amplification and decay in the extended shock precursors on the line and continuum multi-wavelength emission spectra of the shocks. Both Balmer-type and radiative astrophysical shocks are discussed in connection to supernova remnants interacting with partially neutral clouds. Quantitative models described in the review predict a number of observable line-like emission features that can be used to reveal the physical state of the matter in the shock precursors and the character of nonthermal processes in the shocks. Implications of recent progress of gamma-ray observations of supernova remnants in molecular clouds are highlighted.