The Heating of Thermal Electrons in Fast Collisionless Shocks: The Integral Role of Cosmic Rays

Abstract

Understanding the heating of electrons to quasi-thermal energies at collisionless shocks has broad implications for plasma astrophysics. It directly impacts the interpretation of X-ray spectra from shocks, is important for understanding how energy is partitioned between the thermal and cosmic ray populations, and provides insight into the structure of the shock itself. In Ghavamian, Laming & Rakowski (2007) we presented observational evidence for an inverse square relation between the electron-to-proton temperature ratio and the shock speed at the outer blast waves of supernova remnants in partially neutral interstellar gas. There we outlined how lower hybrid waves generated in the cosmic ray precursor could produce such a relationship by heating the electrons to a common temperature independent of both shock speed and the strength of the ambient magnetic field. Here we explore the mechanism of lower hybrid wave heating of electrons in more detail. Specifically we examine the growth rate of the lower hybrid waves for both the kinetic (resonant) and reactive cases. We find that only the kinetic case exhibits a growing mode. At low Alfvén Mach numbers (~15) the growth of lower hybrid waves can be faster than the magnetic field amplification by modified Alfvén waves.

Accepted to ApJ, 25 pages single column, 3 figures

References in corpus (11)

• A Physical Relationship Between Electron-Proton Temperature Equilibration and Mach Number in Fast Collisionless Shocks
• Production of Magnetic Turbulence by Cosmic Rays Drifting Upstream of Supernova Remnant Shocks
• Modeling Bell's Non-resonant Cosmic Ray Instability
• The transport of cosmic rays in self-excited magnetic turbulence
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• A cosmic ray current driven instability in partially ionised media
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• Absence of Electron Surfing Acceleration in a Two-Dimensional Simulation
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Cited by in corpus (12)

• On the electron-ion temperature ratio established by collisionless shocks
• Collisionless shock heating of heavy ions in SN 1987A
• Modeling Bright Gamma-ray and Radio Emission at Fast Cloud Shocks
• On cosmic-ray production efficiency at supernova remnant shocks propagating into realistic diffuse interstellar medium
• Aspect angle for interstellar magnetic field in SN 1006
• High-energy gamma-ray study of the dynamically young SNR G150.3+4.5
• Carbon, Helium and Proton Kinetic Temperatures in a Cygnus Loop Shock Wave
• Electron Heating, Magnetic Field Amplification, and Cosmic Ray Precursor Length at Supernova Remnant Shocks
• X-ray Line Diagnostics of Ion Temperature at Cosmic-Ray Accelerating Collisionless Shocks
• Polarized Balmer Line Emission from Supernova Remnant Shock Waves Efficiently Accelerating Cosmic Rays
• Critical Mach Numbers for Magnetohydrodynamic Shocks with Accelerated Particles and Waves
• Electron Energization in Quasi-Parallel Shocks: Test-Particle-Electrons in a Proton Driven Turbulence