On Bactrian glitch-size distributions

TL;DR

This paper investigates the distribution of pulsar glitch sizes, especially bimodality, using Bayesian analysis and simulations of vortex dynamics under different neutron star models, revealing how various perturbations influence glitch statistics.

Contribution

It introduces a Bayesian approach to analyze glitch size distribution and demonstrates how specific neutron star models can produce bimodal glitch distributions.

Findings

Bimodality in glitch size distribution for PSR J0537-6910.

Annular variation in pinning causes bimodality.

Sectorial triggers weakly induce bimodality.

Abstract

A glitch is a rare and sudden increase in the otherwise steadily decreasing rotation rate of a pulsar. Its cause is widely attributed to the transfer of angular momentum to the crust of the star from the array of superfluid vortices enclosed within. The magnitude of such an increase defines the size of the glitch. The distribution of glitch sizes in individual pulsars, the power-law being the most argued for, is shrouded in uncertainty due to the small sample size. From a Bayesian perspective, we revisit the data for PSR J0537-6910, the pulsar with the most glitches, and find a bimodality in the distribution, reminiscent of the Bactrian camel. To understand this bimodality, we use a superfluid vortex simulator and study three independent neutron star paradigms: (i) Annular variation in pinning strength to account for the predicted differences between the crust and the core; (ii) Sectorial triggers to mimic local disturbances; and (iii) Stress-waves to model global disturbances. We find that annular variation in pinning introduces a bimodality in the glitch-size distribution and that sectorial triggers do so weakly. Stress-waves do not lead to any such features for the range of parameters tested. This provides us with new insights into the effects of various perturbations on the vortex dynamics and the glitch statistics of neutron stars.