Are gravitational waves from giant magnetar flares observable?

TL;DR

This study uses advanced simulations to assess whether giant magnetar flares can produce detectable gravitational waves, finding that typical magnetic fields are unlikely to generate observable signals with current detectors.

Contribution

It provides the first systematic relationship between magnetar surface magnetic field strength and gravitational wave strain using nonlinear general-relativistic magnetohydrodynamics simulations.

Findings

Gravitational wave emissions are highly nonlinear functions of magnetic field strength.

Detection of f-modes excited by magnetic reconfigurations is unlikely with current observatories.

Low-frequency modes up to 100 Hz could be potentially detectable.

Abstract

Are giant flares in magnetars viable sources of gravitational radiation? Few theoretical studies have been concerned with this problem, with the small number using either highly idealized models or assuming a magnetic field orders of magnitude beyond what is supported by observations. We perform nonlinear general-relativistic magnetohydrodynamics simulations of large-scale hydromagnetic instabilities in magnetar models. We utilise these models to find gravitational wave emissions over a wide range of energies, from 10^40 to 10^47 erg. This allows us to derive a systematic relationship between the surface field strength and the gravitational wave strain, which we find to be highly nonlinear. In particular, for typical magnetar fields of a few times 10^15 G, we conclude that a direct observation of f-modes excited by global magnetic field reconfigurations is unlikely with present or near-future gravitational wave observatories, though we also discuss the possibility that modes in a low-frequency band up to 100 Hz could be sufficiently excited to be relevant for observation.