Current closure in the pulsar magnetosphere

TL;DR

This paper proposes a minimal assumption model for pulsar magnetospheres, explaining current closure and charge source distribution, and linking pair production to energy dissipation and high-energy emission.

Contribution

It introduces a simplified, force-free model of the pulsar magnetosphere that accounts for charge supply via pair production at the polar cap rim.

Findings

Charges from the polar cap rim sustain the current sheet.

Maximum potential drop is inversely proportional to pair multiplicity.

Electromagnetic energy dissipation relates to pulsar spindown energy loss.

Abstract

Current closure in the pulsar magnetosphere holds the key to its structure. We must determine not only the global electric circuit, but also the source of its electric charge carriers. We address this issue with the minimum number of assumptions: a) The magnetosphere is everywhere ideal and force-free, except above the polar cap and in some finite part of the current sheet; and b) pairs are produced above the polar cap with multiplicity kappa. We show that a thin region of width delta ~ r_pc/2 kappa << r_pc along the rim of the polar cap provides all the charges that are needed in the equatorial and separatrix electric current sheet. These charges are transferred to the current sheet in a narrow dissipation zone just outside the magnetospheric Y-point. The maximum accelerating potential in this region is equal to the potential drop in the thin polar cap rim, which is approximately equal to 1/kappa times the potential drop from the center to the edge of the polar cap. The dissipated electromagnetic energy is approximately equal to 0.5/kappa times the total pulsar spindown energy loss. Our framework allows to calculate the high energy emission in terms of the pair multiplicity.