Rotating vector model and radius-to-frequency mapping in the presence of multipole magnetic field

TL;DR

This paper extends the rotating vector model and radius-to-frequency mapping to include multipole magnetic fields in pulsars and magnetars, revealing wider beams and unchanged polarization angles, with implications for observed pulse behaviors.

Contribution

It introduces a model considering multipole magnetic fields, showing how they affect pulse width and polarization without altering certain angles, aiding interpretation of pulsar and magnetar observations.

Findings

Multipole fields produce wider radiation beams than dipole fields.

Polarization position angle expression remains unchanged with multipole fields.

Changes in inclination angle and phase constant explain observed polarization variations.

Abstract

The rotating vector model and radius-to-frequency mapping in the presence of multipole magnetic field in pulsars and magnetars are considered. An axisymmetric potential field is assumed. It is found that: (1) The radiation beam in the case of multipole field is wider than the dipole case. This may account the increasing pulse width at higher frequency of pulsars (anti-radius-to-frequency mapping). (2) The expression for the polarization position angle is unchanged. Only the inclination angle {\alpha} and phase constant {\phi}_0 will change. The angle between the rotational axis and line of sight, and the position angle constant {\psi}_0 will not change. When fitting the varying position angle of magnetars, these constraints should be considered. The appearance and disappearance of multipole field may account for the changing slope of position angle in the radio emitting magnetar Swift J1818.0-1607. Similar but more active process in magnetar magnetospheres may account for the diverse position angle in fast radius bursts.