Electron acceleration at pulsar wind termination shocks

Abstract

We study the acceleration of electrons and positrons at an electromagnetically modified, ultra-relativistic shock in the context of pulsar wind nebulae (PWNe). We simulate the outflow produced by an obliquely rotating pulsar in proximity of its termination shock with a two-fluid code which uses a magnetic shear wave to mimic the properties of the wind. We integrate electron trajectories in the test-particle limit in the resulting background electromagnetic fields to analyse the injection mechanism. We find that the shock-precursor structure energizes and reflects a sizeable fraction of particles, which becomes available for further acceleration. We investigate the subsequent first-order Fermi process sustained by small-scale magnetic fluctuations with a Monte Carlo code. We find that the acceleration proceeds in two distinct regimes: when the gyro-radius $r_{\text{g}}$ exceeds the wavelength of the shear $\lambda$, the process is remarkably similar to first-order Fermi acceleration at relativistic, parallel shocks. This regime corresponds to a low density wind which allows the propagation of superluminal waves. When $r_{\text{g}}<\lambda$, which corresponds to the scenario of driven reconnection, the spectrum is softer.

11 pages, 7 figures, 1 table, accepted for publication in the Astrophysical Journal

References in corpus (6)

• Pair production in counter-propagating laser beams
• Pulsar Wind Nebulae as Cosmic Pevatrons: A Current Sheet's Tale
• Relativistic magnetic reconnection in pair plasmas and its astrophysical applications
• Constraints on particle acceleration sites in the Crab Nebula from relativistic MHD simulations
• Very high energy emission as a probe of relativistic magnetic reconnection in pulsar winds
• Particle acceleration in superluminal strong waves

Cited by in corpus (1)

• Interaction of the electro-magnetic precursor from a relativistic shock with the upstream flow. I. Synchrotron absorption of strong electromagnetic waves