GWTC-3: Compact Binary Coalescences Observed by LIGO and Virgo During the Second Part of the Third Observing Run (2111.03606v3)

Abstract: The third Gravitational-Wave Transient Catalog (GWTC-3) describes signals detected with Advanced LIGO and Advanced Virgo up to the end of their third observing run. Updating the previous GWTC-2.1, we present candidate gravitational waves from compact binary coalescences during the second half of the third observing run (O3b) between 1 November 2019, 15:00 UTC and 27 March 2020, 17:00 UTC. There are 35 compact binary coalescence candidates identified by at least one of our search algorithms with a probability of astrophysical origin $p_\mathrm{astro} > 0.5$. Of these, 18 were previously reported as low-latency public alerts, and 17 are reported here for the first time. Based upon estimates for the component masses, our O3b candidates with $p_\mathrm{astro} > 0.5$ are consistent with gravitational-wave signals from binary black holes or neutron star-black hole binaries, and we identify none from binary neutron stars. However, from the gravitational-wave data alone, we are not able to measure matter effects that distinguish whether the binary components are neutron stars or black holes. The range of inferred component masses is similar to that found with previous catalogs, but the O3b candidates include the first confident observations of neutron star-black hole binaries. Including the 35 candidates from O3b in addition to those from GWTC-2.1, GWTC-3 contains 90 candidates found by our analysis with $p_\mathrm{astro} > 0.5$ across the first three observing runs. These observations of compact binary coalescences present an unprecedented view of the properties of black holes and neutron stars.

• The paper presents a comprehensive analysis of 90 gravitational-wave events from compact binary coalescences detected during the third observing run.
• Robust methodologies using pipelines like GstLAL, MBTA, and PyCBC achieved high signal-to-noise ratios and low false alarm rates for the detections.
• Results enhance our understanding of binary system properties and event rates, paving the way for future advancements in multimessenger astronomy.

Gravitational Wave Transients Analysis with LIGO and Virgo Data

The paper under discussion presents a comprehensive analysis of gravitational-wave (GW) transients detected by the Advanced LIGO and Virgo detectors. Utilizing the data obtained during the third observing run (O3), the authors detail the detection of a significant number of transient GW events. The focus is on gravitational waves emitted by coalescing compact binaries, including binary black holes (BBHs), binary neutron stars (BNSs), and neutron star-black hole (NSBH) systems. The paper showcases the identification of multiple new GW events, some with strong statistical significance.

Key numerical highlights from the paper illustrate the expansive dataset analyzed in this paper:

• Number of Events: A total of 90 events have been reported, marking an extension from previous observing runs. Notably, these include 55 events from the O3 run alone.
• False Alarm Rates (FAR): Minimum FARs for recorded events display a wide range, with several events falling below \ensuremath{10^{-5}} yr\ensuremath{^{-1}} indicating extremely low probability of these detections being due to noise.
• Signal-to-Noise Ratio (SNR): The analysis reveals high SNR values for numerous events, surpassing typical thresholds needed to validate GW observations robustly.

The methodological approach involved various pipelines like GstLAL, MBTA, and PyCBC, each contributing uniquely to signal detection and characterization. These independent pipelines enhance cross-validation of detected signals, thereby increasing the robustness of the reported detections.

Regarding the implications for gravitational-wave astrophysics, this immense dataset deepens our understanding of the population properties of coalescing systems, such as mass and spin distributions, and provides critical insights into the rate of such mergers across the universe. Observations of NSBH and BNS systems further reveal possible electromagnetic counterparts which are indispensable for multimessenger astronomy.

Moreover, the paper discusses the challenges and solutions related to data processing, including noise transients and calibration issues, that are crucial for accurate GW signal detection.

Looking forward, as the detectors' sensitivity improves with upcoming upgrades, there is potential for the exploration of fainter GW sources and more diverse astrophysical phenomena. This research provides a baseline for future work in GW astrophysics, including enhanced parameter estimation and understanding the physical mechanisms driving such cosmic events.

The bold claims made regarding some events, particularly those with high SNR and low FAR, challenge conventional understanding of extreme astrophysical systems and warrant further investigation possibly with the aid of simulation or alternative methods. These events pose questions about the population synthesis models currently used in predicting GW event rates and characteristics. Future collaborative efforts integrating GW and electromagnetic observations could significantly augment the scope of discoveries in this domain.

In conclusion, this paper exemplifies the intricate interplay between advanced observational techniques and theoretical models, collectively propelling the field of gravitational-wave astrophysics towards a comprehensive understanding of the universe's most energetic phenomena.