Electron Heating, Magnetic Field Amplification, and Cosmic Ray Precursor Length at Supernova Remnant Shocks

Abstract

We investigate the observability, by direct and indirect means, of a shock precursor arising from magnetic field amplification by cosmic rays. We estimate the depth of such a precursor under conditions of nonresonant amplification, which can provide magnetic field strengths comparable to those inferred for supernova remnants. Magnetic field generation occurs as the streaming cosmic rays induce a plasma return current, and may be quenched either by nonresonant or resonant channels. In the case of nonresonant saturation, the cosmic rays become magnetized and amplification saturates at higher magnetic fields. The precursor can extend out to $10^{17}-10^{18}$ cm and is potentially detectable. If resonant saturation occurs, the cosmic rays are scattered by turbulence and the precursor length will likely be much smaller. The dependence of precursor length on shock velocity has implications for electron heating. In the case of resonant saturation, this dependence is similar to that in the more familiar resonantly generated shock precursor, which when expressed in terms of the cosmic ray diffusion coefficient $\varkappa$ and shock velocity $v_s$ is $\varkappa /v_s$. In the nonresonantly saturated case, the precursor length declines less quickly with increasing $v_s$. Where precursor length proportional to $1/v_s$ gives constant electron heating, this increased precursor length could be expected to lead to higher electron temperatures for nonresonant amplification. This should be expected at faster supernova remnant shocks than studied by previous works. Existing results and new data analysis of SN 1006 and Cas A suggest some observational support for this idea.

34 pages, accepted by ApJ

References in corpus (9)

• A Physical Relationship Between Electron-Proton Temperature Equilibration and Mach Number in Fast Collisionless Shocks
• First detection of VHE gamma-rays from SN 1006 by H.E.S.S
• Characterizing the non-thermal emission of Cas A
• Spatial Structure and Collisionless Electron Heating in Balmer-dominated Shocks
• The gas density around SN 1006
• The First X-Ray Proper-Motion Measurements of the Forward Shock in the Northeastern Limb of SN 1006
• The Heating of Thermal Electrons in Fast Collisionless Shocks: The Integral Role of Cosmic Rays
• A high resolution UV absorption spectrum of supernova ejecta in SN1006
• Mach Number Dependence of Electron Heating in High Mach Number Quasiperpendicular Shocks

Cited by in corpus (5)

• On the electron-ion temperature ratio established by collisionless shocks
• Carbon, Helium and Proton Kinetic Temperatures in a Cygnus Loop Shock Wave
• Wave Propagation at Oblique Shocks: How Did Tycho Get Its Stripes?
• Polarized Balmer Line Emission from Supernova Remnant Shock Waves Efficiently Accelerating Cosmic Rays
• Electron Energization in Quasi-Parallel Shocks: Test-Particle-Electrons in a Proton Driven Turbulence