Properties and observability of glitches and anti-glitches in accreting pulsars

TL;DR

This paper models the properties and observability of glitches and anti-glitches in accreting pulsars, predicting their occurrence rates, magnitudes, and identifying the best candidate for detection with current and future X-ray observatories.

Contribution

It provides the first detailed theoretical predictions of glitches and anti-glitches in accreting pulsars using starquake and superfluid vortex transfer models.

Findings

Glitches caused by starquakes in accreting pulsars are very rare and unlikely to be detected.

Angular momentum transfer can cause more frequent glitches and anti-glitches in accreting pulsars.

GX 1+4 is identified as the best candidate for glitch detection with current and future X-ray instruments.

Abstract

Several glitches have been observed in young, isolated radio pulsars, while a clear detection in accretion-powered X-ray pulsars is still lacking. We use the Pizzochero snowplow model for pulsar glitches as well as starquake models to determine for the first time the expected properties of glitches in accreting pulsars and their observability. Since some accreting pulsars show accretion-induced long-term spin-up, we also investigate the possibility that anti-glitches occur in these stars. We find that glitches caused by quakes in a slow accreting neutron star are very rare and their detection extremely unlikely. On the contrary, glitches and anti-glitches caused by a transfer of angular momentum between the superfluid neutron vortices and the non-superfluid component may take place in accreting pulsars more often. We calculate the maximum jump in angular velocity of an anti-glitch and we find that it is expected to be about 1E-5 - 1E-4 rad/s. We also note that since accreting pulsars usually have rotational angular velocities lower than those of isolated glitching pulsars, both glitches and anti-glitches are expected to have long rise and recovery timescales compared to isolated glitching pulsars, with glitches and anti-glitches appearing as a simple step in angular velocity. Among accreting pulsars, we find that GX 1+4 is the best candidate for the detection of glitches with currently operating X-ray instruments and future missions such as the proposed Large Observatory for X-ray Timing (LOFT).