Article

# Designing a cross‐correlation search for continuous‐wave gravitational radiation from a neutron star in the supernova remnant SNR 1987A★

School of Mathematical Sciences, Rochester Institute of Technology, 85 Lomb Memorial Drive, Rochester, NY 14623, USA

Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.11). 06/2011; 414(3):2650 - 2663. DOI: 10.1111/j.1365-2966.2011.18585.x Get notified about updates to this publication Follow publication |

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**ABSTRACT:**ABSTRACTA strong candidate for a source of gravitational waves is a highly magnetized, rapidly rotating neutron star (magnetar) deformed by internal magnetic stresses. We calculate the mass quadrupole moment by perturbing a zeroth-order hydrostatic equilibrium by an axisymmetric magnetic field with a linked poloidal–toroidal structure. In this work, we do not require the model star to obey a barotropic equation of state (as a realistic neutron star is not barotropic), allowing us to explore the hydromagnetic equilibria with fewer constraints. We derive the relation between the ratio of poloidal to total field energy Λ and ellipticity ε, and briefly compare our results to those obtained using the barotropic assumption. Then, we present some examples of how our results can be applied to astrophysical contexts. First, we show how our formulae, in conjunction with current gravitational wave (non-)detections of the Crab pulsar and the Cassiopeia A central compact object (Cas A CCO), can be used to constrain the strength of the internal toroidal fields of those objects. We find that, for the Crab pulsar (whose canonical equatorial dipole field strength, inferred from spin-down, is 4 × 108 T) to emit detectable gravitational radiation, the neutron star must have a strong toroidal field component, with maximum internal toroidal field strength Btm= 7 × 1012 T; for gravitational waves to be detected from the Cas A CCO at 300 Hz, Btm∼ 1013 T, whereas detection at 100 Hz would require Btm∼ 1014 T. Using our results, we also show how the gravitational wave signal emitted by a magnetar immediately after its birth (assuming it is born rapidly rotating, with Λ≲ 0.2) makes such a newborn magnetar a stronger candidate for gravitational wave detection than, for example, an SGR giant flare. -
##### Article: Updated gravitational-wave upper limits on the internal magnetic field strength of recycled pulsars

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**ABSTRACT:**Recent calculations of the hydromagnetic deformation of a stratified, non-barotropic neutron star are generalized to describe objects with superconducting interiors, whose magnetic permeability μ is much smaller than the vacuum value μ0. It is found that the star remains oblate if the poloidal magnetic field energy is ≳40 per cent of the total magnetic field energy, that the toroidal field is confined to a torus which shrinks as μ decreases and that the deformation is much larger (by a factor of ∼μ0/μ) than that in a non-superconducting object. The results are applied to the latest direct and indirect upper limits on the gravitational-wave emission from the Laser Interferometer Gravitational Wave Observatory (LIGO) and radio pulse timing (spin-down) observations of 81 millisecond pulsars, to show how one can use these observations to infer the internal field strength. It is found that the indirect spin-down limits already imply astrophysically interesting constraints on the poloidal–toroidal field ratio and the diamagnetic shielding factor (by which accretion reduces the observable external magnetic field e.g. by burial). These constraints will improve following gravitational-wave detections, with implications for accretion-driven magnetic field evolution in recycled pulsars and the hydromagnetic stability of these objects’ interiors. - [Show abstract] [Hide abstract]

**ABSTRACT:**The ‘First Generation Era’ of gravitational wave detectors is now over, but the data analysis effort for the search of continuous gravitational waves is still ongoing and active. Many results have been produced but still many searches are underway. I present and discuss here the most recent results for this search, together with short discussions on analysis which are now underway and plans for the near future. The discussion on long-term plans and perspectives for the so-called Advanced Detector Era are beyond the scope of this paper.