Cosmic-ray-induced filamentation instability in collisionless shocks

TL;DR

This study uses large-scale hybrid simulations to explore how accelerated ions induce filamentation and magnetic field amplification in collisionless shocks, potentially explaining observed X-ray structures in supernova remnants.

Contribution

It demonstrates the self-consistent formation of magnetic cavities and filaments caused by cosmic-ray streaming in non-relativistic shocks, revealing new mechanisms of magnetic field amplification.

Findings

Magnetic cavities and filaments are formed by streaming cosmic rays.

Magnetic field amplification reaches factors of 50-100.

Filamentary structures may explain X-ray variability in supernova remnants.

Abstract

We used unprecedentedly large 2D and 3D hybrid (kinetic ions - fluid electrons) simulations of non-relativistic collisionless strong shocks in order to investigate the effects of self-consistently accelerated ions on the overall shock dynamics. The current driven by suprathermal particles streaming ahead of the shock excites modes transverse to the background magnetic field. The Lorentz force induced by these self-amplified fields tends to excavate tubular, underdense, magnetic-field-depleted cavities that are advected with the fluid and perturb the shock surface, triggering downstream turbulent motions. These motions further amplify the magnetic field, up to factors of 50-100 in knot-like structures. Once downstream, the cavities tend to be filled by hot plasma plumes that compress and stretch the magnetic fields in elongated filaments; this effect is particularly evident if the shock propagates parallel to the background field. Highly-magnetized knots and filaments may provide explanations for the rapid X-ray variability observed in RX J1713.7-3946 and for the regular pattern of X-ray bright stripes detected in Tycho's supernova remnant.