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

TL;DR

For the first time, the nature of gravitational-wave polarizations from the antenna response of the LIGO-Virgo network is tested, thus enabling a new class of phenomenological tests of gravity.

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.

Figures (4)

• Figure 1: The GW event GW170814 observed by LIGO Hanford, LIGO Livingston, and Virgo. Times are shown from August 14, 2017, 10:30:43 UTC. Top row: SNR time series produced in low latency and used by the low-latency localization pipeline on August 14, 2017. The time series were produced by time shifting the best-match template from the online analysis and computing the integrated SNR at each point in time. The single-detector SNRs in Hanford, Livingston, and Virgo are 7.3, 13.7, and 4.4, respectively. Second row: Timefrequency representation of the strain data around the time of GW170814. Bottom row: Time-domain detector data (in color), and$90 \%$ confidence intervals for waveforms reconstructed from a morphology-independent wavelet analysis [13] (light gray) and BBH models described in Sec. V (dark gray), whitened by each instrument's noise amplitude spectral density between 20 Hz and 1024 Hz . For this figure the data were also low passed with a 380 Hz cutoff to eliminate out-of-band noise. The whitening emphasizes different frequency bands for each detector, which is why the reconstructed waveform amplitude evolution looks different in each column. The left ordinate axes are normalized such that the physical strain of the wave form is accurate at 130 Hz . The right ordinate axes are in units of whitened strain, divided by the square root of the effective bandwidth ( 360 Hz ), resulting in units of noise standard deviations.
• Figure 2: Amplitude spectral density of strain sensitivity of the Advanced LIGO-Advanced Virgo network, estimated using 4096 s of data around the time of GW170814. Here, several known linearly coupled noise sources have been removed from the data.
• Figure 3: Localization of GW170814. The rapid localization using data from the two LIGO sites is shown in yellow, with the inclusion of data from Virgo shown in green. The full Bayesian localization is shown in purple. The contours represent the$90 \%$ credible regions. The left panel is an orthographic projection and the inset in the center is a gnomonic projection; both are in equatorial coordinates. The inset on the right shows the posterior probability distribution for the luminosity distance, marginalized over the whole sky.
• Figure 4: Posterior probability density for the source-frame masses$m_{1}$ and $m_{2}(t o p)$ and the effective inspiral and precession spin parameters, $\chi_{\text{eff }}$ and $\chi_{p}$ (bottom) measured at a gravitational-wave frequency of 20 Hz , well before the merger. The dashed lines mark the $90 \%$ credible interval for the one-dimensional marginalized distributions. The two-dimensional plots show the contours of the $50 \%$ and $90 \%$ credible regions plotted over a color-coded posterior density function. For GW170814, both $\chi_{\text{eff }}$ and $\chi_{p}$ are influenced by their respective prior distributions, shown in green. While the GW observation provides additional constraints for the $\chi_{\text{eff }}$ posterior, there is only a marginal information gain for $\chi_{p}$. (Kullback-Leibler divergence between the prior and posterior distribution of 0.08 nat [4,129,130].)