Polarized emission from of an off-centred dipole

TL;DR

This paper extends the rotating vector model for pulsar radio polarization to include off-centred dipoles, providing an exact analytic expression and highlighting the altitude dependence of polarization angle.

Contribution

It introduces a generalized model for pulsar polarization that accounts for off-centred dipoles and derives an exact analytic formula for phase-resolved polarization angle.

Findings

Polarization angle depends on emission altitude for off-centred dipoles.

The model's parameter space increases, but remains manageable for statistical analysis.

Frequency evolution of polarization angle indicates off-centred magnetic dipoles.

Abstract

Radio polarization measurements of pulsed emission from pulsars offer a valuable insight into the basic geometry of the neutron star: inclination angle between the magnetic and rotation axis and inclination of the line of sight. So far, all studies about radio polarization focused on the standard rotating vector model with the underlying assumption of a centred dipole. In this letter, we extend this model to the most general off-centred dipole configuration and give an exact closed analytic expression for the phase-resolved polarization angle. It is shown that contrary to the rotating vector model, for an off-centred dipole, the polarization angle also depends on the emission altitude. Although the fitting parameter space increases from two to six (position of the dipole, altitude and shift of the zero phase), statistical analysis should remain tractable. Observations revealing an evolution of the polarization angle with frequency would undeniably furnish a strong hint for the presence of a decentred magnetic dipole in neutron stars.