Adjustment of the electric current in pulsar magnetospheres and origin of subpulse modulation

TL;DR

This paper presents a model explaining pulsar subpulse modulation through electric current adjustments in the magnetosphere, leading to narrow plasma streams that account for observed emission patterns.

Contribution

It introduces a novel model linking current mismatch and reverse plasma flows to the formation of circulating plasma streams in pulsar magnetospheres.

Findings

Streams have a radius about 10% of the polar cap, matching observed subbeam structures.

The model explains the carousel and nested cone beam features of pulsar emission.

Electric drift is minimal due to small potential drops in narrow gaps.

Abstract

The subpulse modulation of pulsar radio emission goes to prove that the plasma flow in the open field line tube breaks into isolated narrow streams. I propose a model which attributes formation of streams to the process of the electric current adjustment in the magnetosphere. A mismatch between the magnetospheric current distribution and the current injected by the polar cap accelerator gives rise to reverse plasma flows in the magnetosphere. The reverse flow shields the electric field in the polar gap and thus shuts up the plasma production process. I assume that a circulating system of streams is formed such that the upward streams are produced in narrow gaps separated by downward streams. The electric drift is small in this model because the potential drop in narrow gaps is small. The gaps have to drift because by the time a downward stream reaches the star surface and shields the electric field, the corresponding gap has to shift. The transverse size of the streams is determined by the condition that the potential drop in the gaps is sufficient for the pair production. This yields the radius of the stream roughly 10% of the polar cap radius, which makes it possible to fit in the observed morphological features such as the "carousel" with 10-20 subbeams and the system of the core - two nested cone beams.