[Paper Review] 4-OGC: Catalog of gravitational waves from compact-binary mergers

A. Nitz, S. Kumar+6 more|arXiv (Cornell University)|Dec 13, 2021

Pulsars and Gravitational Waves Research79 references21 citations

TL;DR

This paper presents the 4-OGC catalog, a comprehensive analysis of 94 compact-binary mergers (90 BBHs, 2 NSBHs, 2 BNSs) from Advanced LIGO and Virgo's O1–O3b runs (2015–2020), including 7 new high-significance BBH detections from O3b. The key contribution is the inclusion of updated parameter estimates accounting for instrumental calibration uncertainty and a full set of sub-threshold candidates, with GW200318_191337 identified as a potentially distant merger at redshift 0.84.

ABSTRACT

We present the fourth Open Gravitational-wave Catalog (4-OGC) of binary neutron star (BNS), binary black hole (BBH) and neutron star-black hole (NSBH) mergers. The catalog includes observations from 2015-2020 covering the first through third observing runs (O1, O2, O3a, O3b) of Advanced LIGO and Advanced Virgo. The updated catalog includes 7 BBH mergers which were not previously reported with high significance during O3b for a total of 94 observations: 90 BBHs, 2 NSBHs, and 2 BNSs. The most confident new detection, GW200318_191337, has component masses $49.1^{+16.4}_{-12.0} extrm{M}_\odot$ and $31.6^{+12.0}_{-11.6} extrm{M}_\odot$; its redshift of $0.84^{+0.4}_{-0.35}$ ($90\%$ credible interval) may make it the most distant merger so far. We estimate the merger rate of BBH sources, assuming a powerlaw mass distribution containing an additive Gaussian peak, to be $16.5_{-6.2}^{+10.4} (25.0_{-8.0}^{+12.6})$ Gpc$^{-3}$ yr$^{-1}$ at a redshift of $z=0$ ($0.2$). For BNS and NSBH sources, we estimate a merger rate of $200^{+309}_{-148}$ Gpc$^{-3}$ yr$^{-1}$ and $19^{+30}_{-14}$ Gpc$^{-3}$ yr$^{-1}$, respectively, assuming the known sources are representative of the total population. We provide reference parameter estimates for each of these sources using an up-to-date model accounting for instrumental calibration uncertainty. The corresponding data release also includes our full set of sub-threshold candidates.

Motivation & Objective

• To provide a comprehensive, publicly available catalog of gravitational-wave signals from compact-binary mergers detected during the first four observing runs of Advanced LIGO and Advanced Virgo.
• To improve parameter estimation by incorporating instrumental calibration uncertainty into the analysis of gravitational-wave signals.
• To identify and validate new high-significance BBH mergers from the second half of O3b (O3b), which were previously unreported.
• To estimate population-level merger rates for BBH, BNS, and NSBH systems using the observed sample and a power-law plus Gaussian peak mass model.
• To release a full set of sub-threshold candidates to support cross-observational follow-up studies with electromagnetic, neutrino, or optical data.

Proposed method

• Conducted a deep archival search of public LIGO and Virgo data from 2015 to 2020, covering O1, O2, O3a, and O3b observing runs.
• Applied a Bayesian inference framework to compute posterior distributions for source parameters, including component masses, redshift, and spin, with marginalization over calibration uncertainty.
• Used a significance threshold of P_astro > 0.5 or false alarm rate < once per 100 years to define confident detections.
• Modelled the BBH merger rate with a power-law mass distribution augmented by a Gaussian peak to account for high-mass systems.
• Estimated BNS and NSBH merger rates assuming the observed sources are representative of the full population, using the same likelihood framework.
• Released all sub-threshold candidates and full parameter estimates in a companion data release for broader community use.

Experimental results

Research questions

• RQ1 What is the full set of compact-binary merger signals detected in the first four observing runs of Advanced LIGO and Advanced Virgo?
• RQ2 Which new high-significance BBH mergers were identified in the O3b data segment that were not previously reported?
• RQ3 How do instrumental calibration uncertainties affect the posterior estimates of gravitational-wave source parameters?
• RQ4 What are the population-level merger rates for binary black holes, binary neutron stars, and neutron star–black hole systems?
• RQ5 How can sub-threshold candidates be used to support multi-messenger follow-up studies across different astronomical datasets?

Key findings

• The 4-OGC catalog includes 94 confident compact-binary merger detections: 90 binary black holes, 2 neutron star–black hole systems, and 2 binary neutron stars.
• Seven new high-significance BBH mergers were detected in O3b, including GW200318_191337 with component masses of 49.1⁺¹⁶.⁴₋₁₂.⁰ M☉ and 31.6⁺¹².⁰₋₁₁.⁶ M☉, and a redshift of 0.84⁺⁰.⁴₋₀.³⁵, suggesting it may be the most distant merger observed.
• The BBH merger rate is estimated at 16.5⁺¹⁰.⁴₋⁶.² Gpc⁻³ yr⁻¹ (z=0) or 25.0⁺¹².⁶₋⁸.⁰ Gpc⁻³ yr⁻¹ (z=0.2), assuming a power-law mass distribution with a Gaussian peak.
• The BNS merger rate is estimated at 200⁺³⁰⁹₋¹⁴⁸ Gpc⁻³ yr⁻¹, and the NSBH rate at 19⁺³⁰₋¹⁴ Gpc⁻³ yr⁻¹, based on the observed sample.
• The catalog provides reference parameter estimates for all 94 sources using an up-to-date model that accounts for instrumental calibration uncertainty, improving posterior accuracy.
• A complete data release includes all sub-threshold candidates, enabling future cross-correlation studies with gamma-ray bursts, high-energy neutrinos, and optical transients.