GW170814: A Three-Detector Observation of Gravitational Waves from a Binary Black Hole Coalescence (1709.09660v3)

Abstract: 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 $\lesssim$ 1 in 27000 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 $30.5_{-3.0}^{+5.7}$ Msun and $25.3_{-4.2}^{+2.8}$ Msun (at the 90% credible level). The luminosity distance of the source is $540_{-210}^{+130}~\mathrm{Mpc}$, 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.

• The paper reports the first three-detector observation of gravitational waves from a binary black hole merger, improving event localization from 1160 to 60 square degrees.
• It achieves high detection confidence with a matched-filter SNR of 18 and a Bayes factor over 1600, resulting in a false alarm rate of ≤ 1 in 27,000 years.
• The inclusion of Advanced Virgo enabled the first tests of gravitational-wave polarization, reinforcing general relativity over alternative theories.

Observation and Analysis of Gravitational Waves: GW170814 Event

The paper "GW170814: A Three-Detector Observation of Gravitational Waves from a Binary Black Hole Coalescence" is a significant contribution to the field of gravitational-wave astronomy, detailing the first three-detector observation of gravitational waves (GWs) by the LIGO and Virgo collaborations. The inclusion of the Advanced Virgo detector alongside the two Advanced LIGO detectors marks a pivotal step in enhancing the detection capabilities and localization precision of gravitational wave events.

This observation took place on August 14, 2017, when a transient gravitational-wave signal, generated from the coalescence of two stellar-mass black holes, was detected. The Advanced Virgo's involvement in this observation crucially reduced the 90% credible region from 1160 square degrees (with only the two LIGO detectors) to just 60 square degrees. This increased precision in localization emanates from the triangulation capabilities offered by an expanded detector network. The stellar-mass black holes involved had masses estimated to be 30.5 and 25.3 solar masses, positioned at a luminosity distance of 540 Mpc, equating to a redshift of approximately 0.11.

Of notable significance is the ability to test gravitational-wave polarizations, a potential that is unlocked with the additional Virgo detector. While standard general relativity (GR) predicts two tensor polarizations, alternate gravitational theories propose additional modes. The LIGO-Virgo network permits the first geometrical tests of these polarization states, with the analysis indicating a strong preference for the standard tensorial mode over potential scalar or vector modes, lending additional empirical support to GR in the strong-field regime.

The three-detector network not only enhances detection reliability, achieving a matched-filter signal-to-noise ratio of 18 and an exceedingly low false-alarm rate (≤ 1 in 27,000 years), but also advances the scientific exploration of gravity itself. With a calculated Bayes factor exceeding 1600 favoring the GW signal model over noise within Virgo, the robustness of this event's detection and characterization is notable.

Furthermore, the research underscores the importance of multidisciplinary follow-up observations. Here, 25 facilities engaged in exploring potential electromagnetic counterparts—even though no counterparts were detected for GW170814, emphasizing the challenge yet critical importance of comprehensive follow-up in GW astronomy.

Looking forward, the implications of GW170814 suggest a strengthened foundation for gravitational-wave astronomy and a promising avenue for testing alternative gravitational theories. Future developments in detector sensitivity and the continued collaboration between LIGO and Virgo will likely yield further insights into astrophysical phenomena and gravitational dynamics. As the operational network matures, we can expect an enhancement in the catalog of observed GW events, further enriching our understanding of the universe's most extreme environments and the fundamental nature of gravity.