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<SUB>-3.0</SUB><SUP>+5.7</SUP>M<SUB>☉</SUB> and 25 .3<SUB>-4.2</SUB><SUP>+2.8</SUP>M<SUB>☉</SUB> (at the 90% credible level). The luminosity distance of the source is 54 0<SUB>-210</SUB><SUP>+130</SUP> Mpc , corresponding to a redshift of z =0.1 1<SUB>-0.04</SUB><SUP>+0.03</SUP>. A network of three detectors improves the sky localization of the source, reducing the area of the 90% credible region from 1160 deg<SUP>2</SUP> using only the two LIGO detectors to 60 deg<SUP>2</SUP> 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.