Crab flares due to turbulent dissipation of the pulsar striped wind

TL;DR

This paper explains the gamma-ray flares from the Crab Nebula as caused by turbulence in the pulsar's electromagnetic wind, which accelerates particles and produces observable synchrotron emission modulated by upstream plasma dynamics.

Contribution

It introduces a turbulence-based model for Crab flares, linking upstream wind instability to particle acceleration and flare emission, supported by force-free electrodynamics simulations.

Findings

Turbulence in the pulsar wind triggers gamma-ray flares.

Simulations show the wind becomes fully turbulent before the termination shock.

Flares occur when the high-energy cutoff surpasses nebular emission around 0.1-1 GeV.

Abstract

We interpret $\gamma$-ray flares from the Crab Nebula as the signature of turbulence in the pulsar's electromagnetic outflow. Turbulence is triggered upstream by dynamical instability of the wind's oscillating magnetic field, and accelerates non-thermal particles. On impacting the wind termination shock, those particles emit a distinct synchrotron component $F_{\nu,\rm flare}$, which is constantly modulated by intermittency of the upstream plasma flow. Flares are observed when the high-energy cutoff of $F_{\nu,\rm flare}$ emerges above the fast-declining nebular emission around 0.1 - 1 GeV. Simulations carried out in the force-free electrodynamics approximation predict the striped wind to become fully turbulent well ahead of the wind termination shock, provided its terminal Lorentz factor is $\lesssim 10^4$.