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Constraining the inclinations of binary mergers from gravitational-wave observations

Usman, S. A., Mills, J. C. ORCID: and Fairhurst, S. ORCID: 2019. Constraining the inclinations of binary mergers from gravitational-wave observations. Astrophysical Journal 877 (2) , 82. 10.3847/1538-4357/ab0b3e

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Much of the information we hope to extract from the gravitational-wave signatures of compact binaries is only obtainable when we can accurately constrain the inclination of the orbital plane relative to the line of sight. In this paper, we discuss in detail a degeneracy between the measurement of the binary distance and inclination that limits our ability to accurately measure the inclination using gravitational waves alone. This degeneracy is exacerbated by the expected distribution of events in the universe, which leads us to prefer face-on systems at a greater distance. We use a simplified model that only considers the binary distance and orientation and show that this gives comparable results to the full parameter estimates obtained from the binary neutron star merger GW170817. For the advanced LIGO-Virgo network, it is only binaries that are close to edge-on, i.e., with inclinations ι gsim 75°, that will be distinguishable from face-on systems. Extended networks that have good sensitivity to both gravitational-wave polarizations will only be able to constrain the inclination of a face-on binary at a signal-to-noise ratio of 20 to ι lesssim 45°. Even for loud signals with signal-to-noise ratios of 100, face-on signals will only be constrained to have inclinations $\iota \lesssim 30^\circ $. In the absence of observable higher modes or orbital precession, this degeneracy will dominate the mass measurements of binary black hole mergers at cosmological distances.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Publisher: American Astronomical Society
ISSN: 0004-637X
Date of First Compliant Deposit: 3 July 2019
Date of Acceptance: 26 February 2019
Last Modified: 09 May 2023 02:21

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