Polar-cap accelerator and radio emission from pulsars

TL;DR

This paper investigates the physics of polar caps in pulsars with arbitrary current ratios, revealing conditions for activity, discharge processes, and a new mechanism for pulsar radio emission involving Alfven waves and electromagnetic radiation.

Contribution

It extends pulsar polar cap models to arbitrary current ratios, identifying conditions for activity and proposing a novel wave-based radio emission mechanism.

Findings

No significant activity for 0<α<1

High voltage and discharge occur for α>1 or α<0

Proposes Alfven wave conversion as a pulsar radio emission mechanism

Abstract

Electric currents j flow along the open magnetic field lines from the polar caps of neutron stars. Activity of a polar cap depends on the ratio \alpha=j/c\rho_GJ, where \rho_GJ is the corotation charge density. The customary assumption \alpha\approx 1 is not supported by recent simulations of pulsar magnetospheres and we study polar caps with arbitrary \alpha. We argue that no significant activity is generated on field lines with 0<\alpha<1. Charges are extracted from the star and flow along such field lines with low energies. By contrast, if \alpha>1 or \alpha<0, a high voltage is generated, leading to unsteady e^+- discharge on a scale-height smaller than the size of the polar cap. The discharge can power observed pulsars. Voltage fluctuations in the discharge imply unsteady twisting of the open flux tube and generation of Alfven waves. These waves are ducted along the tube and converted to electromagnetic waves, providing a new mechanism for pulsar radiation.