Discovery of the first anti-glitch event in the rotation-powered pulsar PSR B0540-69

TL;DR

This paper reports the first detection of an anti-glitch in a rotation-powered pulsar, PSR B0540-69, characterized by a sudden spin-down without accompanying radiative or burst activity, suggesting an internal origin.

Contribution

It presents the first observation of an anti-glitch in a rotation-powered pulsar, expanding understanding of neutron star rotational irregularities beyond magnetars and accreting pulsars.

Findings

Detected a permanent spin frequency decrease of approximately 1.04e-7 Hz.

No associated burst activity or pulse profile change observed.

Supports a possible internal superfluid mechanism for anti-glitches.

Abstract

Using data from the Neutron star Interior Composition ExploreR (NICER) observatory, we identified a permanent spin frequency decrease of $\Delta\nu=-(1.04\pm0.07)\times 10^{-7}\,\mathrm{Hz}$ around MJD 60132 in the rotation-powered pulsar PSR B0540-69, which exhibits a periodic signal at a frequency of $\nu\sim 19.6\,\mathrm{Hz}$. This points to an anti-glitch event, a sudden decrease of the pulsar's rotational frequency without any major alteration in the pulse profile or any significant increase of the pulsed flux. Additionally, no burst activity was observed in association with the anti-glitch. To date, observations of the few known anti-glitches have been made in magnetars or accreting pulsars. This is the first anti-glitch detected in a rotation-powered pulsar. Given its radiatively quiet nature, this anti-glitch is possibly of internal origin. Therefore, we tentatively frame this event within a proposed mechanism for anti-glitches where the partial `evaporation' of the superfluid component leads to an increase of the normal component's moment of inertia and a decrease of the superfluid one.