Force-Free Electrodynamics of Pulsars

TL;DR

This paper demonstrates that Force-Free Electrodynamics (FFE) effectively models pulsar magnetospheres but requires additional current-generation models to determine unique solutions, with implications for pulsar spin-down and braking indices.

Contribution

It shows FFE's applicability to pulsar magnetospheres and highlights the need for models of current generation to select physical solutions.

Findings

FFE describes pulsar magnetospheres even with significant radiation and particle wind.

Multiple stationary FFE solutions exist with different current configurations.

Calculated Poynting power ranges for aligned rotator magnetospheres.

Abstract

We show that FFE (Force-Free Electrodynamics) describes pulsar magnetospheres -- even when radiation and particle wind power are comparable to the spin-down power. At the same time, we show that FFE is insufficient for calculating pulsar magnetospheres. This is because FFE admits a large family of stationary solutions with different currents flowing in the closed line region. To choose the actual solution one needs a model of current generation which goes beyond pure FFE. We calculate several FFE magnetospheres for the aligned rotator. The Poynting power of these solutions fills the range $c^{-3}\mu ^2\Omega^4~< ~L~ <~ 0.67 c^{-3}\mu ^2\Omega^4(c/\Omega R_s)^2$, for angular velocity $\Omega$ and magnetic field which is a pure dipole $\mu$ on the surface of the star of radius $R_s$. Anomalous braking indices of young pulsars might be explained by currents flowing in the closed-line region.