Turbulent amplification of magnetic field driven by dynamo effect at rippled shocks

TL;DR

This paper analytically investigates how rippled shocks in magnetohydrodynamics amplify magnetic fields through the dynamo effect, providing explicit growth rates and saturation conditions relevant to supernova remnants.

Contribution

It presents the first analytical derivation of magnetic field amplification and saturation at rippled shocks, extending previous numerical studies.

Findings

Magnetic field can be amplified up to milligauss levels.

Analytic expressions for growth rate and saturation are derived.

Results explain short-term X-ray variability in supernova remnants.

Abstract

We derive analytically the vorticity generated downstream of a two-dimensional rippled hydromagnetic shock neglecting fluid viscosity and resistivity. The growth of the turbulent component of the downstream magnetic field is driven by the vortical eddies motion. We determine an analytic time-evolution of the magnetic field amplification at shocks, so far described only numerically, until saturation occurs due to seed-field reaction to field lines whirling. The explicit expression of the amplification growth rate and of the non-linear field back-reaction in terms of the parameters of shock and interstellar density fluctuations is derived from MHD jump conditions at rippled shocks. A magnetic field saturation up to the order of milligauss and a short-time variability in the $X$-ray observations of supernova remnants can be obtained by using reasonable parameters for the interstellar turbulence.