Maximum gravitational-wave energy emissible in magnetar flares

TL;DR

This paper explores the maximum gravitational-wave energies that magnetar flares can emit, showing that energies up to 10^{48}-10^{49} erg are possible under more typical conditions than previously thought, with implications for current and future observations.

Contribution

It demonstrates that high gravitational-wave energies are achievable in magnetar flares without requiring extreme conditions, expanding the potential energy range beyond earlier models.

Findings

Maximum GW energy emissions of 10^{48}-10^{49} erg are possible in magnetar flares.

Current GW observational limits are approaching these maximum energies.

More generic conditions, including magnetic energy tapping and core cracking, can produce these energies.

Abstract

Recent searches of gravitational-wave (GW) data raise the question of what maximum GW energies could be emitted during gamma-ray flares of highly magnetized neutron stars (magnetars). The highest energies (\sim 10^{49} erg) predicted so far come from a model [K. Ioka, Mon. Not. Roy. Astron. Soc. 327, 639 (2001)] in which the internal magnetic field of a magnetar experiences a global reconfiguration, changing the hydromagnetic equilibrium structure of the star and tapping the gravitational potential energy without changing the magnetic potential energy. The largest energies in this model assume very special conditions, including a large change in moment of inertia (which was observed in at most one flare), a very high internal magnetic field, and a very soft equation of state. Here we show that energies of 10^{48}-10^{49} erg are possible under more generic conditions by tapping the magnetic energy, and we note that similar energies may also be available through cracking of exotic solid cores. Current observational limits on gravitational waves from magnetar fundamental modes are just reaching these energies and will beat them in the era of advanced interferometers.