Theory of Stochastic Shock Drift Acceleration for Electrons in the Shock Transition Region

Abstract

We propose a novel electron acceleration mechanism, which we call stochastic shock drift acceleration (SSDA), that extends the standard shock drift acceleration (SDA) for low-energy electrons at a quasi-perpendicular shock to include the effect of stochastic pitch-angle scattering. We demonstrate that the steady-state energy spectrum of electrons accelerated within the shock transition region becomes a power-law in the limit of strong scattering. The spectral index is independent of the pitch-angle scattering coefficient. On the other hand, the maximum energy attainable through the mechanism scales linearly with the pitch-angle scattering coefficient. These results have been confirmed by Monte Carlo simulations that include finite pitch-angle anisotropy. We find that the theory can reasonably well explain in-situ observations of quasi-perpendicular Earth's bow shock. Theoretical scaling law suggests that the maximum energy increases in proportion to the square of the shock speed, indicating that the thermal electrons may be accelerated up to mildly relativistic energies by the SSDA at quasi-perpendicular supernova remnant shocks. Therefore, the mechanism provides a plausible solution to the long-standing electron injection problem.

15 pages, 6 figures, Accepted for the publication in ApJ

References in corpus (4)

• Electron Shock Surfing Acceleration in Multidimensions: Two-dimensional Particle-In-Cell Simulation of Collisionless Perpendicular Shock
• Electron Surfing and Drift Accelerations in a Weibel-dominated High-Mach-number Shock
• A critical Mach number for electron injection in collisionless shocks
• An in situ comparison of electron acceleration at collisionless shocks under differing upstream magnetic field orientations

Cited by in corpus (21)

• Observational Evidence for Stochastic Shock Drift Acceleration of Electrons at the Earth's Bow Shock
• Magnetic field amplification by the Weibel instability at planetary and astrophysical high-Mach-number shocks
• Theory of Electron Injection at Oblique Shock of Finite Thickness
• Electron Acceleration at Rippled Low-Mach-number Shocks in High-beta Collisionless Cosmic Plasmas
• Shock-accelerated electrons during the fast expansion of a coronal mass ejection
• Non-linear diffusive shock acceleration: A recipe for injection of electrons
• Cosmic Ray Acceleration and Nonthermal Radiation at Accretion Shocks in the Outer Regions of Galaxy Clusters
• Pre-acceleration in the Electron Foreshock I: Electron Acoustic Waves
• Electron acceleration at supernova remnants
• Electron Preacceleration at Weak Quasi-perpendicular Intracluster Shocks: Effects of Preexisting Nonthermal Electrons
• A data-driven physics-based transport model of solar energetic particles accelerated by coronal mass ejection shocks propagating through the solar coronal and heliospheric magnetic fields
• Pre-acceleration in the Electron Foreshock II: Oblique Whistler Waves
• Stochastic re-acceleration and magnetic-field damping in Tycho's supernova remnant
• Mach Number Dependence of Ion-scale Kinetic Instability at Collisionless Perpendicular Shock: Condition for Weibel-dominated Shock
• In-situ Measurement of the Energy Fraction in Supra-thermal and Energetic Particles at ACE, Wind, and PSP Interplanetary Shocks
• Electron shock drift acceleration at a low-Mach-number, low-plasma-beta quasi-perpendicular shock
• Electron Heating in 2D Particle-in-Cell Simulations of Quasi-Perpendicular Low-Beta Shocks
• SLAMS-Propelled Electron Acceleration at High-Mach Number Astrophysical Shocks
• Current sheets, plasmoids and flux ropes in the heliosphere. Part II: Theoretical aspects
• The mechanism of efficient electron acceleration at parallel non-relativistic shocks
• Transport of electrons in tangled magnetic fields