Analysis of Crab X-Ray Polarization Using Deeper Imaging X-Ray Polarimetry Explorer Observations

Abstract

<p>We present Crab X-ray polarization measurements using Imaging X-Ray Polarimetry Explorer (IXPE) data<br>with a total exposure of 300 ks, three times more than the initial 2022 discovery paper. Polarization is detected<br>in three times more pulsar phase bins, revealing an S-shaped +40° polarization angle sweep in the main pulse<br>and >1σ departures from the OPTIMA optical polarization in both pulses, suggesting different radiation<br>mechanisms or sites for the polarized emission at the two wavebands. Our polarization map of the inner nebula<br>reveals a toroidal magnetic field, as seen in prior IXPE analyses. Along the southern jet, the magnetic field<br>orientation relative to the jet axis changes from perpendicular to parallel and the polarization degree decreases<br>by ∼6%. These observations may be explained by kink instabilities along the jet or a collision with a dense, jetdeflecting medium at the tip. Using spectropolarimetric analysis, we find asymmetric polarization in the four<br>quadrants of the inner nebula, as expected for a toroidal field geometry, and a spatial correlation between<br>polarization degree and photon index.<br></p>