Josephine Wong, Jack T. Dinsmore, Roger W. Romani, Stefano Silvestri, Shumeng Zhang, Ruolan Jin, Matteo Bachetti, C. Y. Ng, Niccolo Di Lalla, Wei Deng, Fei Xie, Patrick Slane, Niccolo Bucciantini, Philip Kaaret, Tsunefumi Mizuno, Maura Pilia, Yi-Jung Yang, Silvia Zane, Martin C. Weisskopf

We present the first X-ray polarization measurements of the PSR/PWN complex within SNR Kes 75. Two $\rm {\sim}\,500\,ks$ IXPE observations were conducted in October/November 2024 and April 2025. The second observation yields a significant phase-average 2-8 keV polarization degree $\rm PD = 9.9\% \pm 2.5\%$ at $\rm PA=36.8^\circ \pm 7.3^\circ$, implying a toroidal field aligned with the PWN symmetry axis. The first epoch, however, has only a polarization upper limit. During this epoch, an additional pulsed component is visible at $Δφ\approx 0.5$, detected at ${\sim}\,3.7σ$. An unbinned phase-resolved analysis reveals a high-PD rotating vector model PA sweep at the ${\sim}\,99.5\%$ confidence level, with angles fixed at those inferred from the PWN morphology; this can explain the loss of phase-average polarization. Additional observations are needed to pin down the nature of the anomalous pulse.