Frequency Spectrum of Gravitational Radiation from Global Hydromagnetic Oscillations of a Magnetically Confined Mountain on an Accreting Neutron Star

Abstract

Recent time-dependent, ideal magnetohydrodynamic (ideal-MHD) simulations of polar magnetic burial in accreting neutron stars have demonstrated that stable, magnetically confined mountains form at the magnetic poles, emitting gravitational waves at f* (stellar spin frequency) and 2f*. Global MHD oscillations of the mountain, whether natural or stochastically driven, act to modulate the gravitational wave signal, creating broad sidebands (FWHM ~0.2f*) in the frequency spectrum around f* and 2f*. The oscillations can enhance the signal-to-noise ratio achieved by a long-baseline interferometer with coherent matched filtering by up to 15%, depending on where f* lies relative to the noise curve minimum. Coherent, multidetector searches for continuous waves from nonaxisymmetric pulsars should be tailored accordingly.