IXPE view of the Crab pulsar following the 17 July and 6 August 2025 glitches

TL;DR

This study used IXPE X-ray polarimetry to investigate potential changes in the Crab pulsar's polarization properties following two small glitches in 2025, finding no significant variations and constraining the maximum change in magnetic obliquity.

Contribution

First detailed phase-resolved X-ray polarimetric analysis of the Crab pulsar before and after small glitches, providing constraints on magnetospheric changes.

Findings

No significant change in polarization detected post-glitch

Maximum change in magnetic obliquity constrained to ±4°

Optical and X-ray lag remained consistent before and after glitches

Abstract

The Crab pulsar experienced two relatively small glitches separated by only 20 days in September and October 2025. IXPE observed the source twice, with delay times since the glitch epoch ranging between 35 and 75 days, depending on the observation. We carried out a multi-method analysis to investigate whether there is evidence for significant changes in the polarization properties of the pulsar, underlying possible variations in the pulsar magnetosphere itself following the glitches. Specifically, we performed: (1) phase-averaged polarimetry of the Crab pulsar before and after the glitches, following an approach similar to that adopted in 2019 by PolarLight, a non-imaging CubeSat-class photoelectric polarimeter which observed a change in the X-ray polarization within 100 days after a stronger glitch in July 2019; (2) a comparison, before and after the glitch, of phase-resolved X-ray polarimetry with IXPE, not possible with PolarLight. Furthermore, we investigated, by means of phase-resolved optical (OPTIMA) polarimetry, whether a significant change in the X-to-optical lag was present in the data before and after the glitch. We find no evidence of a change in the polarization for the pulsar emission before and after the glitch, We use the upper limits obtained to estimate the maximum change in magnetic obliquity allowed by the data, using the standard rotating vector model and assuming that the glitch is due to a neutron-star quake. We constrain this maximum change to be no greater than $\pm4^{o}$ at the 95\% confidence level.