The population of pulsars with interpulses and the implications for beam evolution

TL;DR

This paper investigates pulsar interpulses and beam evolution, suggesting that magnetic axes tend to align over time, which impacts models of pulsar populations and challenges standard spin-down formulas.

Contribution

It demonstrates that pulsar beam evolution involves alignment over 70 million years, providing a new perspective on pulsar population estimates and magnetic axis behavior.

Findings

Alignment timescale of 70 million years consistent with independent methods

Random magnetic axis distribution incompatible with observed interpulse fractions

Standard spin-down formula's validity is questionable

Abstract

The observed fraction of pulsars with interpulses, their period distribution and the observed pulse width versus pulse period correlation is shown to be inconsistent with a model in which the angle alpha between the magnetic axis and the rotation axis is random. This conclusion appears to be unavoidable, even when non-circular beams are considered. Allowing the magnetic axis to align from a random distribution at birth with a timescale of 70 Myrs years can, however, explain those observations well. The timescale derived is consistent with that obtained via independent methods. The probability that a pulsar beam intersects the line of sight is a function of the angle alpha and therefore beam evolution has important consequences for evolutionary models and for estimations of the total number of neutron stars. The validity of the standard formula for the spin-down rate, which is independent of alpha appears to be questionable.