GW170814: A Three-Detector Observation of Gravitational Waves from a Binary Black Hole Coalescence

On August 14, 2017 at 10∶30: 43 UTC, the Advanced Virgo detector and the two Advanced LIGO detectors coherently observed a transient gravitational-wave signal produced by the coalescence of two stellar mass black holes, with a false-alarm rate of ≲1 in 27 000 years. The signal was observed with a three-detector network matched-filter signal-to-noise ratio of 18. The inferred masses of the initial black holes are 30. 5-₃. ₀^+5. 7M⊙ and 25. 3-₄. ₂^+2. 8M⊙ (at the 90% credible level). The luminosity distance of the source is 540-₂₁₀^+130 Mpc, corresponding to a redshift of z=0. 11-₀. ₀₄^+0. 03. A network of three detectors improves the sky localization of the source, reducing the area of the 90% credible region from 1160 deg^2 using only the two LIGO detectors to 60 deg^2 using all three detectors. For the first time, we can test the nature of gravitational-wave polarizations from the antenna response of the LIGO-Virgo network, thus enabling a new class of phenomenological tests of gravity.