Probing the Origin of Magnetar X-ray Polarization Diversity: A Multi-wavelength Geometrical Study of 1E 1547.0-5408 and 1E 2259+586

TL;DR

This study investigates how viewing geometry influences the observed X-ray polarization diversity in magnetars, using Bayesian models on two sources with contrasting polarization levels to understand the underlying physics.

Contribution

It provides a systematic geometrical analysis of two magnetars with different polarization degrees, highlighting the role of viewing geometry and intrinsic physics in polarization diversity.

Findings

Both magnetars show no evidence of strong, static global twists.

The polarization difference is mainly due to viewing geometry and emission physics.

Models favor a nearly aligned configuration when radio data are included.

Abstract

The exceptionally high X-ray polarization recently detected in the magnetar 1E 1547.0-5408 is considered a strong candidate signature of quantum electrodynamic vacuum birefringence, an interpretation that hinges critically on the source's viewing geometry. This stark contrast to the typically lower polarization degrees seen in other magnetars prompts a fundamental question: to what extent does viewing geometry, rather than intrinsic physics, drive the observed polarization diversity? To answer this, we perform a systematic, comparative geometrical analysis of two magnetars representing opposite extremes: the high-polarization source 1E 1547.0-5408 and the low-polarization source 1E 2259+586. The data are modelled within a unified Bayesian framework with both the classical rotating vector model (CRVM) and a twisted-magnetosphere extension (MRVM). For 1E 2259+586, both models favour a geometry with moderate magnetic inclination and viewing angles but a small impact angle. By combining the single-epoch phase-resolved fit with three-epoch phase-averaged position angle measurements, we find no significant secular evolution of the twist parameter \lambda and derive a conservative upper limit of |\Delta\lambda|<0.79 at the 95 per cent level over 26 day. For 1E 1547.0-5408, the observed position angle curve is already well reproduced by the CRVM, while the MRVM shows no statistically significant advantage. When radio-informed priors are imposed, the posterior shifts towards a nearly aligned configuration consistent with the radio constraints.Both sources show no evidence for strong, static global twists in the current epoch. The observed polarization dichotomy arises from the confluence of viewing geometry, intrinsic surface emission physics, and magnetospheric propagation effects.