Gravitational wave emission from rotating superfluid neutron stars

In this paper, we investigate the effect of a pinned superfluid component on the gravitational wave emission of a steadily rotating deformed neutron star. We show that the superfluid pinning allows the possibility for there to be gravitational wave emission at both the stellar spin frequency Ω and its first harmonic, 2Ω. This contrasts with the conventional case where there is no pinned superfluidity, where either only the 2Ω harmonic is present or else the star undergoes precession, a feature which is not believed to be common in the known pulsar population. This work motivates the carrying out of gravitational wave searches where both the Ω and 2Ω harmonics are searched for, even in targeted searches for waves from known pulsars which are not observed to precess. Observation of such a two-component signal would provide evidence in favour of pinned superfluidity inside the star.