Polarization as a tool to uncover properties of highly-magnetized accreting neutron stars

Observations of highly-magnetized accreting neutron stars, known as X-ray pulsars (XRPs), carried out by the Imaging X-ray Polarimetry Explorer (IXPE) have provided completely new insight into these fascinating objects, thanks to the indispensable information embedded in their X-ray polarization. X-ray polarimetry allows us to measure the polarization angle (PA) and degree (PD) as a function of pulse phase for XRPs, where essentially the PA gives us information on the geometry of the pulsar and the PD tells us something about the underlying beam pattern. Additionally, the radiation from XRPs was expected to be highly polarized, with estimates for a PD of up to 80% for favorable orientations.

I will discuss the theoretical expectations for the polarization properties of XRPs before the launch of IXPE, subsequently giving an overview of the results of IXPE’s observations of X-ray pulsars so far. I will present a summary of the results of the entire sample, as well as provide highlights of individual XRPs that have provided particularly intriguing results. I will discuss the implications of these results, as well as possible explanations for the unexpectedly low PDs.