Explaining radio emission of magnetars via rotating and oscillating magnetospheres of neutron stars

TL;DR

This paper explores how the magnetosphere conditions of magnetars, including rotation and oscillations, influence their ability to emit radio waves, explaining why some magnetars are radio-quiet and others can emit radio signals.

Contribution

It introduces a model considering relativistic effects and oscillations to explain the radio emission thresholds in magnetars, aligning with observational data.

Findings

Larger star compactness raises the radio death-line.

Oscillations lower the death-line, enabling radio emission.

Radio emission correlates with magnetar burst activity.

Abstract

We investigate the conditions for radio emission in rotating and oscillating magnetars, by focusing on the main physical processes determining the position of their death-lines in the P-\dot{P} diagram, i.e. of those lines that separate the regions where the neutron star may be radio-loud or radio-quiet. After using the general relativistic expression for the electromagnetic scalar potential in the magnetar magnetosphere, we find that larger compactness parameters of the star as well as larger inclination angles between the rotation axis and the magnetic moment produce death-lines well above the majority of known magnetars. This is consistent with the observational evidence of no regular radio emission from the magnetars in the frequency range typical for the ordinary pulsars. On the contrary, when oscillations of the magnetar are taken into account, the death-lines shift downward and the conditions necessary for the generation of radio emission in the magnetosphere are met. Present observations showing a close connection between the burst activity of magnetars and the generation of the radio emission in the magnetar magnetosphere are naturally accounted for within our interpretation.