Stochastic background of gravitational waves emitted by magnetars

TL;DR

This paper models the cosmological gravitational wave background from young, fast-spinning magnetars with various magnetic field configurations, predicting detectable signals for future ground-based interferometers.

Contribution

It introduces a numerical model linking magnetar magnetic fields and spin evolution to gravitational wave background predictions, considering different internal and external magnetic field configurations.

Findings

Strongest signals from magnetars with intense internal toroidal fields (~10^{16} G).

Detectable gravitational wave background predicted for third-generation interferometers.

Significant variation in background depending on magnetic field models.

Abstract

Two classes of high energy sources in our galaxy are believed to host magnetars, neutron stars whose emission results from the dissipation of their magnetic field. The extremely high magnetic field of magnetars distorts their shape, and causes the emission of a conspicuous gravitational waves signal if rotation is fast and takes place around a different axis than the symmetry axis of the magnetic distortion. Based on a numerical model of the cosmic star formation history, we derive the cosmological background of gravitational waves produced by magnetars, when they are very young and fast spinning. We adopt different models for the configuration and strength of the internal magnetic field (which determines the distortion) as well as different values of the external dipole field strength (which governs the spin evolution of magnetars over a wide range of parameters). We find that the expected gravitational wave background differs considerably from one model to another. The strongest signals are generated for magnetars with very intense toroidal internal fields ($\sim 10^{16}$ G range) and external dipole fields of $\sim 10^{14}$, as envisaged in models aimed at explaining the properties of the Dec 2004 giant flare from SGR 1806-20. Such signals should be easily detectable with third generation ground based interferometers such as the Einstein Telescope.