X-ray Polarimetry of X-ray Pulsars

• Main Authors: Poutanen, Juri, Tsygankov, Sergey S, Forsblom, Sofia V
• Format: Journal Article
• Language: English
• Published: 08-08-2024
• Subjects: Physics - High Energy Astrophysical Phenomena; Physics - Solar and Stellar Astrophysics
• DOI: 10.48550/arxiv.2408.04431

Galaxies, 12 (2024) 46 Radiation from X-ray pulsars (XRPs) was expected to be strongly linearly
polarized owing to a large difference in their ordinary and extraordinary mode
opacities. The launch of IXPE allowed us to check this prediction. IXPE
observed a dozen X-ray pulsars, discovering pulse-phase dependent variation of
the polarization degree (PD) and polarization angle (PA). Although the PD
showed rather erratic profiles resembling flux pulse dependence, the PA in most
cases showed smooth variations consistent with the rotating vector model (RVM),
which can be interpreted as a combined effect of vacuum birefringence and
dipole magnetic field structure at a polarization-limiting (adiabatic) radius.
Application of the RVM allowed us to determine XRP geometry and to confirm the
free precession of the NS in Her X-1. Deviations from RVM in two bright
transients led to the discovery of an unpulsed polarized emission likely
produced by scattering off the accretion disk wind.