Pulsar Pair Cascades in a Distorted Magnetic Dipole Field

TL;DR

This paper explores how distortions in a neutron star's magnetic dipole field can enhance pair production in pulsars, potentially explaining observed pulsar behaviors and their contribution to cosmic rays.

Contribution

It introduces a simple model for a distorted dipole magnetic field that significantly affects pair cascade multiplicity and the pulsar death line, expanding understanding of pulsar emission mechanisms.

Findings

Distorted magnetic fields increase pair multiplicity.

The pulsar death line shifts downward, allowing more pulsars to produce pairs.

Implications for pulsar population and cosmic ray positrons.

Abstract

We investigate the effect of a distorted neutron star dipole magnetic field on pulsar pair cascade multiplicity and pair death lines. Using a simple model for a distorted dipole field that produces an offset polar cap, we derive the accelerating electric field above the polar cap in space charge limited flow. We find that even a modest azimuthally asymmetric distortion can significantly increase the accelerating electric field on one side of the polar cap and, combined with a smaller field line radius of curvature, leads to larger pair multiplicity. The death line for producing pairs by curvature radiation moves downward in the P-Pdot diagram, allowing high pair multiplicities in a larger percentage of the radio pulsar population. These results could have important implications for the radio pulsar population, high energy pulsed emission and the pulsar contribution to cosmic ray positrons.