Rotating vector model for magnetars

TL;DR

This paper extends the rotating vector model to account for twisted magnetic fields in magnetars, showing how polarization angles evolve with magnetospheric untwisting, aiding in magnetic field geometry analysis from radio observations.

Contribution

It introduces a modified rotating vector model for magnetars with twisted magnetic fields and provides a way to infer magnetic geometry from polarization data.

Findings

Polarization position angle changes due to magnetic twist.

Untwisting magnetosphere causes monotonic evolution of polarization.

Order of magnitude estimation formula for magnetic field geometry.

Abstract

The modification of the rotating vector model in the case of magnetars are calculated. Magnetars may have twisted magnetic field compared with normal pulsars. The polarization position angle of magnetars will change in the case of a twisted magnetic field. For a twisted dipole field, we found that the position angle will change both vertically and horizontally. During the untwisting process of the magnetar magnetosphere, the modifications of the position angle will evolve with time monotonously. This may explain the evolution of the position angle in magnetar PSR J1622-4950 and XTE J1810-197. The relation between the emission point and the line of sight will also change. We suggest every magnetospheric models of magnetars also calculate the corresponding changes of position angle in their models. Order of magnitude estimation formula for doing this is given. This opens the possibility to extract the magnetic field geometry of magnetars from their radio polarization observations.