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Search for Continuous Gravitational Waves from Scorpius X-1 in LIGO O2 Data

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Zhang,  Yuanhao
Searching for Continuous Gravitational Waves, AEI-Hannover, MPI for Gravitational Physics, Max Planck Society;

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Papa,  Maria Alessandra
Searching for Continuous Gravitational Waves, AEI-Hannover, MPI for Gravitational Physics, Max Planck Society;

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Observational Relativity and Cosmology, AEI-Hannover, MPI for Gravitational Physics, Max Planck Society;

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2011.04414.pdf
(Preprint), 2MB

Zhang_2021_ApJL_906_L14.pdf
(Publisher version), 831KB

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Citation

Zhang, Y., Papa, M. A., Krishnan, B., & Watts, A. L. (2021). Search for Continuous Gravitational Waves from Scorpius X-1 in LIGO O2 Data. The Astrophysical Journal Letters, 906(2): L14. doi:10.3847/2041-8213/abd256.

Cite as: http://hdl.handle.net/21.11116/0000-0007-7663-5
Abstract
We present the results of a search in LIGO O2 public data for continuous gravitational waves from the neutron star in the low-mass X-ray binary Scorpius X-1. We search for signals with $\approx$ constant frequency in the range 40-180 Hz. Thanks to the efficiency of our search pipeline we can use a long coherence time and achieve unprecedented sensitivity, significantly improving on existing results. This is the first search that has been able to probe gravitational wave amplitudes that could balance the accretion torque at the neutron star radius. Our search excludes emission at this level between 67.5 Hz and 131.5 Hz, for an inclination angle $44^\circ \pm 6^\circ$ derived from radio observations (Fomalont et al. 2001), and assuming that the spin axis is perpendicular to the orbital plane. If the torque arm is $\approx$ 26 km -- a conservative estimate of the \alfven\ radius -- our results are more constraining than the indirect limit across the band. This allows us to exclude certain mass-radius combinations and to place upper limits on the strength of the star's magnetic field. We also correct a mistake that appears in the literature in the equation that gives the gravitational wave amplitude at the torque balance (Abbott et al. 2017b, 2019a) and we re-interpret the associated latest LIGO/Virgo results in light of this.