Discovery of energy-dependent phase variations in the polarization angle of Cen X-3

TL;DR

This study uncovers complex, energy-dependent polarization angle variations in Cen X-3, driven by phase-dependent scattering in the disk wind, using detailed polarimetric and spectroscopic analysis across multiple X-ray observatories.

Contribution

It introduces a two-component polarization model explaining phase-dependent energy variations, advancing understanding of scattering effects in X-ray pulsars.

Findings

Phase-dependent polarization angle variations are significant.

A two-component model explains complex polarization behavior.

Wind properties modulate with pulse phase, affecting polarization.

Abstract

We present a detailed polarimetric analysis of Cen X-3 using \ixpe observations during its high state, revealing complex energy-dependent polarization behavior. While phase-averaged polarization shows marginal energy dependence, phase-resolved analysis reveals that the energy dependence of the polarization angle (PA) is strongly phase-dependent, with dramatic variations visible in a few specific phase intervals. We model this behavior using a two-component polarization framework consisting of a pulsed component governed by the Rotating Vector Model (RVM) and an additional phase-dependent component. By allowing the additional component's polarized flux to vary with pulse phase while fixing its PA, the observed complex behavior can be reconciled with a single set of RVM parameters across all energies. Spectroscopic analysis using \ixpe, \nicer and \nustar during the high state reveals phase-modulated intrinsic hydrogen column density and covering fraction, suggesting that the wind properties are modulated with pulse phase. Our findings indicate that phase-dependent scattering in the disk wind may significantly alter the observed polarization properties of X-ray pulsars.