Pulsar magnetic alignment and the pulsewidth-age relation

TL;DR

This study analyzes pulsewidth data from 872 pulsars to investigate their magnetic alignment and the pulsewidth-age relation, providing evidence for alignment over about 1 million years and challenging previous models.

Contribution

It offers new evidence for pulsar magnetic alignment occurring faster than previously thought, with a larger variability, and refines models of pulsar evolution based on a larger young pulsar sample.

Findings

Strong evidence for magnetic alignment over ~1 Myr

Alignment time-scale shorter than previous estimates

Best-fit models suggest pulsars are born with random inclination angles

Abstract

Using pulsewidth data for 872 isolated radio pulsars we test the hypothesis that pulsars evolve through a progressive narrowing of the emission cone combined with progressive alignment of the spin and magnetic axes. The new data provide strong evidence for the alignment over a time-scale of about 1 Myr with a log standard deviation of around 0.8 across the observed population. This time-scale is shorter than the time-scale of about 10 Myr found by previous authors, but the log standard deviation is larger. The results are inconsistent with models based on magnetic field decay alone or monotonic counter-alignment to orthogonal rotation. The best fits are obtained for a braking index parameter n_gamma approximately equal to 2.3, consistent the mean of the six measured values, but based on a much larger sample of young pulsars. The least-squares fitted models are used to predict the mean inclination angle between the spin and magnetic axes as a function of log characteristic age. Comparing these predictions to existing estimates it is found that the model in which pulsars are born with a random angle of inclination gives the best fit to the data. Plots of the mean beaming fraction as a function of characteristic age are presented using the best-fitting model parameters.