Gravitational Waves from Magnetars

TL;DR

This paper explores gravitational wave emission mechanisms from magnetars, highlighting their spectral features, impact on braking indices, and potential for probing magnetar properties through rapid charge-discharge processes.

Contribution

It introduces new models for gravitational wave emission from magnetar magnetospheres and discusses their effects on braking indices and observational signatures.

Findings

Spectral features can identify magnetar-origin gravitational waves.

Large magnetic fields can cause braking indices to exceed 3.

Rapid charge-discharge in polar gaps can produce detectable gravitational waves.

Abstract

We study the emission of gravitational waves produced by the magnetosphere of magnetars. We argue that several features in the spectrum could facilitate the identification of that source. In addition, in cases of extremely large magnetic fields we demonstrate that this emission can make the braking index of such stars to be well over 3, which is the standard prediction of the magnetic dipole radiation and aligned rotator mechanisms. A similar picture arises if one focuses on the second braking index. Moreover the braking index depends on both the rotational frequency and the strength of the magnetic field in striking difference from the other mechanisms. We also show that gravitational waves can be produced by polar gap regions due to their rapid charge-discharge process that takes place in timescales from nanosec to microsec. This can provide an alternative way to probe magnetars and test the polar gap model.