GWTC-1: A Gravitational-Wave Transient Catalog of Compact Binary Mergers Observed by LIGO and Virgo during the First and Second Observing Runs (1811.12907v3)

Abstract: We present the results from three gravitational-wave searches for coalescing compact binaries with component masses above 1$\mathrm{M}\odot$ during the first and second observing runs of the Advanced gravitational-wave detector network. During the first observing run (O1), from September $12^\mathrm{th}$, 2015 to January $19^\mathrm{th}$, 2016, gravitational waves from three binary black hole mergers were detected. The second observing run (O2), which ran from November $30^\mathrm{th}$, 2016 to August $25^\mathrm{th}$, 2017, saw the first detection of gravitational waves from a binary neutron star inspiral, in addition to the observation of gravitational waves from a total of seven binary black hole mergers, four of which we report here for the first time: GW170729, GW170809, GW170818 and GW170823. For all significant gravitational-wave events, we provide estimates of the source properties. The detected binary black holes have total masses between $18.6{-0.7}^{+3.2}\mathrm{M}_\odot$, and $84.4_{-11.1}^{+15.8} \mathrm{M}\odot$, and range in distance between $320{-110}^{+120}$ Mpc and $2840_{-1360}^{+1400}$ Mpc. No neutron star - black hole mergers were detected. In addition to highly significant gravitational-wave events, we also provide a list of marginal event candidates with an estimated false alarm rate less than 1 per 30 days. From these results over the first two observing runs, which include approximately one gravitational-wave detection per 15 days of data searched, we infer merger rates at the 90% confidence intervals of $110\, -\, 3840$ $\mathrm{Gpc}^{-3}\,\mathrm{y}^{-1}$ for binary neutron stars and $9.7\, -\, 101$ $\mathrm{Gpc}^{-3}\,\mathrm{y}^{-1}$ for binary black holes assuming fixed population distributions, and determine a neutron star - black hole merger rate 90% upper limit of $610$ $\mathrm{Gpc}^{-3}\,\mathrm{y}^{-1}$.

• The paper presents a detailed catalog of 11 GW events, including 10 BBH mergers and the landmark BNS event GW170817.
• It employs three search algorithms with Bayesian inference to precisely estimate key source parameters from LIGO/Virgo data.
• The findings constrain merger rates and inform models of black hole formation and neutron star EOS, advancing GW astrophysics.

Analysis of GWTC-1: A Gravitational-Wave Transient Catalog

The publication "GWTC-1: A Gravitational-Wave Transient Catalog of Compact Binary Mergers Observed by LIGO and Virgo during the First and Second Observing Runs" provides a comprehensive analysis of gravitational-wave (GW) detections from compact binary mergers. This catalog, spanning two observing runs (O1 and O2) of advanced LIGO and Virgo detectors, is seminal in unraveling the astrophysical properties and rates of binary black hole (BBH) and binary neutron star (BNS) mergers.

Summary of Observations

During O1 and O2, the detectors observed 11 confident GW events—10 BBH mergers and one BNS merger. Notably, the catalog reports four BBH events (GW170729, GW170809, GW170818, and GW170823) for the first time during the O2 run. The remarkable detection of GW170817, a BNS merger, heralds a new avenue for multi-messenger astronomy, providing deep insights into the equation of state (EOS) of neutron stars.

Each GW event has been meticulously analyzed to estimate key source parameters such as component masses, spins, and luminosity distance. For instance, GW170729, previously unpublished, is identified as the highest-mass BBH observed, with a total mass of 84.4 M⊙, indicating potential astrophysical scenarios leading to such massive black holes. On the other hand, GW170817's detection offers precise measurements of neutron star properties and implies constraints on NS EOS.

Methodology and Data Analysis

The analysis employs three distinct GW search methodologies: PyCBC, GstLAL, and coherent WaveBurst (cWB). These methods—targeting modeled and unmodeled transient signals—have been refined post-O1, ensuring enhanced detection confidence and parameter estimation accuracy. The deployment of Bayesian inference using advanced waveform models underpins the extraction of binary parameters and accounts for calibration uncertainties with rigorous statistical treatments.

Implications and Merger Rates

Inferred merger rates at the 90% confidence interval, leveraging approximately one detection per 15 days, are determined for BBHs and BNSs. Binary neutron stars reveal a rate of 110–3840 Gpc⁻³y⁻¹ while the BBH mergers report a broader rate of 9.7–101 Gpc⁻³y⁻¹.

The paper draws attention to the parameter space exploration of BBH and BNS systems, emphasizing the significance of spin distributions and mass ratios. The inferred mass distributions suggest non-uniform origins, possibly linked to different stellar evolution channels. The constraints on NSBH mergers, with an upper limit of 610 Gpc⁻³y⁻¹, further encapsulate the observational challenge in verifying this merger type.

Astrophysical and Theoretical Insights

The findings accentuate the lack of definitive observations within the so-called "mass gaps" of compact objects, thereby prompting continued investigation of stellar evolution predictions. The weakly constrained spin magnitudes and orientations in BBH mergers suggest intricate formation histories, potentially involving dynamical interactions in dense stellar environments.

GW170817 sets a precedent for testing gravitational theories in strong-field regimes, stimulating discussions on the coupling of gravitational and electromagnetic observations. These detected GWs strengthen our understanding of binary coalescence physics, contributing to the burgeoning field of GW astrophysics.

Future Outlook

This paper paves the way for subsequent observing runs, anticipating increased GW detections with enhanced detector sensitivities and the anticipated inclusion of KAGRA into the network. The mathematical and observational rigor exercised in this catalog forms a benchmark for future detections, promising further refinement of binary population characteristics, EOS constraints, and deeper insights into the fundamental forces shaping the cosmos.

In conclusion, the GWTC-1 catalog comprehensively encapsulates early but critical strides in GW astronomy, elucidating the complexity and diversity inherent in the universe's compact binary systems. It highlights the subtle interplay of advanced detection techniques and robust statistical methodologies that collectively broaden our cosmic perspective.