Emission Properties of Periodic Fast Radio Bursts from the Motion of Magnetars: Testing Dynamical Models

TL;DR

This paper proposes a magnetar-based model for the periodic activity of FRB 180916, explaining polarization and frequency-dependent activity windows, and distinguishes it from other models like orbital occultation or forced precession.

Contribution

It introduces a curvature radiation emission model from asymmetric magnetar regions that accounts for observed FRB periodicity and polarization features, supporting a freely precessing magnetar scenario.

Findings

Bursts arrive earlier at higher frequencies, consistent with the magnetar emission model.

Chromatic activity windows challenge orbital occultation models.

Observational tests can differentiate between magnetar precession theories.

Abstract

Recent observations of the periodic Fast Radio Burst source 180916.J0158+65 (FRB 180916) find small linear polarization position angle swings during and between bursts, with a burst activity window that becomes both narrower and earlier at higher frequencies. Although the observed chromatic activity window disfavors models of periodicity in FRB 180916 driven by the occultation of a neutron star by the optically-thick wind from a stellar companion, the connection to theories where periodicity arises from the motion of a bursting magnetar remains unclear. In this paper, we show how altitude-dependent radio emission from magnetar curvature radiation, with bursts emitted from regions which are asymmetric with respect to the magnetic dipole axis, can lead to burst activity windows and polarization consistent with the recent observations. In particular, the fact that bursts arrive systematically earlier at higher frequencies disfavors theories where the FRB periodicity arises from forced precession of a magnetar by a companion or fallback disk, but is consistent with theories where periodicity originates from a slowly-rotating or freely-precessing magnetar. Several observational tests are proposed to verify/differentiate between the remaining theories, and pin-down which theory explains the periodicity in FRB 180916.