Electron Acceleration in the Crab Nebula

TL;DR

This paper investigates how electrons and positrons are accelerated at the Crab Nebula's termination shock, showing that charge separation and turbulence influence their energy spectra and emission, with implications for cosmic-ray composition.

Contribution

It demonstrates that drift motion and turbulence at the shock lead to charge-specific acceleration, reproducing observed X-ray spectra and suggesting charge asymmetry in pulsar wind nebulae.

Findings

Electrons and positrons are accelerated via first-order Fermi process near the shock.

Energy spectra follow a power-law distribution.

Reproduces Crab Nebula's X-ray flux and photon index with turbulence considerations.

Abstract

We study electron and positron acceleration at the termination shock of a striped pulsar wind. Drift motion along the shock surface keeps either electrons or positrons -but not both, close to the equatorial plane of the pulsar, where they are accelerated by the first-order Fermi process. Their energy spectrum is a power law, and both the X-ray flux and photon index of the Crab Nebula, as measured by NuSTAR, can be reproduced for sufficiently large downstream turbulence levels. The implication that one sign of charge is preferentially accelerated in pulsar wind nebulae is potentially important for the interpretation of the positron fraction in cosmic-rays.