Kavli Affiliate: Roger Romani
| Summary:
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 $Δφapprox 0.5$, 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.
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