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

Figures (7)

• Figure 1: ( a) Histogram of Crab pulsar glitch sizes, shown as fractional frequency steps $\Delta\nu/\nu$ (log-scaled x–axis). Vertical markers indicate the glitches on 2019-07-23, 2025-07-17, and 2025-08-06. Historical events are compiled from the ATNF Pulsar Glitch Database for PSR B0531+21/J0534+2200 Manchester2005, the 2019 event parameters are from Shaw2019, and the two 2025 glitches are from Shaw2025Shaw2025b. ( b) Histogram of inter-glitch waiting times for the Crab pulsar glitches. The x–axis is logarithmic and bins are thin to show the multi–decadal spread in intervals. Vertical markers label the waiting time immediately preceding three highlighted events: 2019-07-23 ($\Delta t = 216.87\,\mathrm{d}$), 2025-07-17 ($\Delta t = 2186.38\,\mathrm{d}$), and 2025-08-06 ($\Delta t = 19.95\,\mathrm{d}$).
• Figure 2: Global polarization properties of the Crab pulsar and nebula (integrating all emission in a region within 2.5 arcmin of the PSR), in terms of normalized Stokes parameters for the electric field vector polarization angle (EVPA). The PF is expressed as percentage. Values have been obtained with the PCUBE algorithm of ixpeobssim.
• Figure 3: Space resolved and phase integrated polarization properties of the Crab nebula and pulsar in the 2-8 keV band: left panel Q/I, central panel U/I and right panel PF. Data have been smoother with a Gaussian kernel (5 arcsec width), and limited to pixels having intensity above 0.5% of the maximum. Maps have been obtained with the PMAPCUBE algorithm of ixpeobssim. See for comparison Bucciantini2023.
• Figure 4: Pre- and Post-Glitch Crab Pulsar Polarization obtained with Simultaneous Fitting. The method fits for the phase-varying pulsar and spatially-varying nebula polarization simultaneously using a known fixed flux model. Only ${>}\,2.8\sigma$ measurements are shown. No measurements at this significance level were found outside the Main Pulse (left) and Interpulse (right). Merged (orange) and individual Sep/Oct (green/red) post-glitch data are shown and are ${<}\,3\sigma$ from pre-glitch polarization at the same phase bin. Pre-glitch polarization were measured in Wong2024.
• Figure 5: Sep/Oct (left/right) Post-Glitch Crab Nebula Polarization Maps obtained with Simultaneous Fitting. Matched colorbars range from PF = 8% -- 51%. Black vectors indicate magnetic field direction ($={\rm PA}+90^\circ$). Magenta Chandra contours are overlaid for reference. $5\sigma$ significance cut and 10,000-count flux cut have been applied.