Banks of templates for all-sky narrow-band searches of gravitational waves from spinning neutron stars

Abstract

We construct efficient banks of templates suitable for all-sky narrow-band searches of almost monochromatic gravitational waves originating from spinning neutron stars in our Galaxy in data collected by interferometric detectors. We consider waves with one spindown parameter included and we assume that both the position of the gravitational-wave source in the sky and the wave's frequency together with spindown parameter are unknown. In the construction we employ simplified model of the signal with constant amplitude and phase which is a linear function of unknown parameters. Our template banks enable usage of the fast Fourier transform algorithm in the computation of the maximum-likelihood $\mathcal{F}$-statistic for nodes of the grids defining the bank and fulfill an additional constraint needed to resample the data to barycentric time efficiently. All these template bank features were employed in the recent all-sky $\mathcal{F}$-statistic-based search for continuous gravitational waves in Virgo VSR1 data [J.Aasi et al., Classical Quantum Gravity 31, 165014 (2014)]. Here we improve that template bank by constructing templates suitable for larger range of search parameters and of smaller thicknesses for certain values of search parameters. One of our template banks has thickness 12% smaller than the thickness of the template bank used in the all-sky search of Virgo VSR1 data and only 4% larger than the thickness of 4-dimensional optimal lattice covering $A_4^\star$.