Highly magnetized region in pulsar wind nebulae and origin of the Crab gamma-ray flares

TL;DR

This paper proposes that the Crab nebula's gamma-ray flares originate from magnetic dissipation in a highly magnetized polar region, where kink instability accelerates particles producing observed synchrotron emission.

Contribution

It introduces a model where magnetic dissipation occurs in the polar flow of the nebula, explaining the origin of gamma-ray flares through kink instability and relativistic magnetic loops.

Findings

Magnetic dissipation occurs at the base of the jet in the polar region.

Kink instability triggers magnetic energy release in the flow.

Particle acceleration leads to gamma-ray emission in the hundreds MeV band.

Abstract

The recently discovered gamma-ray flares from the Crab nebula are generally attributed to the magnetic energy release in a highly magnetized region within the nebula. I argue that such a region naturally arises in the polar region of the inner nebula. In pulsar winds, efficient dissipation of the Poynting flux into the plasma energy occur only in the equatorial belt where the energy is predominantly transferred by alternating fields. At high latitudes, the pulsar wind remains highly magnetized therefore the termination shock in the polar region is weak and the postshock flow remains relativistic. I study the structure of this flow and show that the flow at first expands and decelerates and then it converges and accelerates. In the converging part of the flow, the kink instability triggers the magnetic dissipation. The energy release zone occurs at the base of the observed jet. A specific turbulence of relativistically shrinking magnetic loops efficiently accelerates particles so that the synchrotron emission in the hundreds MeV band, both persistent and flaring, comes from this site.