On the Angular Momentum Extraction from the Rotation Powered Pulsars

TL;DR

This paper investigates how angular momentum is extracted from rotation-powered pulsars, focusing on energy deposition within the light cylinder and its effects on magnetospheric currents and emission phases.

Contribution

It introduces new insights into the role of magnetospheric currents and energy flux beyond the light cylinder in angular momentum loss mechanisms.

Findings

Outer magnetosphere compensates for insufficient angular momentum loss.

Enhanced energy flux beyond the light cylinder varies with phase.

Magnetospheric currents inside the star efficiently transfer angular momentum.

Abstract

The rotation powered pulsar loses angular momentum at a rate of the rotation power divided by the angular velocity $\Omega_*$. This means that the length of the lever arm of the angular momentum extracted by the photons, relativistic particles and wind must be on average $c/\Omega_*$, which is known as the light cylinder radius. Therefore, any deposition of the rotation power within the light cylinder causes insufficient loss of angular momentum. In this paper, we investigate two cases of this type of energy release: polar cap acceleration and Ohmic heating in the magnetospheric current inside the star. As for the first case, the outer magnetosphere beyond the light cylinder is found to compensate the insufficient loss of the angular momentum. We argue that the energy flux coming from the sub-rotating magnetic field lines must be larger than the solid-angle average value, and as a result, an enhanced energy flux emanating beyond the light cylinder is observed in different phases in the light curve from those of emission inside the light cylinder. As for the second case, the stellar surface rotates more slowly than the stellar interior. We find that the way the magnetospheric current closes inside the star is linked to how the angular momentum is transferred inside the star. We obtain numerical solutions which show that the magnetospheric current inside the star spreads over the polar cap magnetic flux embedded in the star in such a way that electromotive force is gained efficiently.