[Paper Review] Search for gravitational-lensing signatures in the full third observing run of the LIGO-Virgo network

The LIGO Scientific Collaboration, The Virgo Collaboration+1693 more|arXiv (Cornell University)|Apr 17, 2023

Pulsars and Gravitational Waves Research19 citations

TL;DR

The paper reports a search for gravitational-lensing signatures in the full third observing run (O3) data from the LIGO–Virgo network, detailing methodology and findings on lensing-related signatures in gravitational-wave events.

ABSTRACT

Gravitational lensing by massive objects along the line of sight to the source causes distortions of gravitational wave-signals; such distortions may reveal information about fundamental physics, cosmology and astrophysics. In this work, we have extended the search for lensing signatures to all binary black hole events from the third observing run of the LIGO--Virgo network. We search for repeated signals from strong lensing by 1) performing targeted searches for subthreshold signals, 2) calculating the degree of overlap amongst the intrinsic parameters and sky location of pairs of signals, 3) comparing the similarities of the spectrograms amongst pairs of signals, and 4) performing dual-signal Bayesian analysis that takes into account selection effects and astrophysical knowledge. We also search for distortions to the gravitational waveform caused by 1) frequency-independent phase shifts in strongly lensed images, and 2) frequency-dependent modulation of the amplitude and phase due to point masses. None of these searches yields significant evidence for lensing. Finally, we use the non-detection of gravitational-wave lensing to constrain the lensing rate based on the latest merger-rate estimates and the fraction of dark matter composed of compact objects.

Motivation & Objective

• Motivate and define the search for gravitational-lensing signatures in the LIGO–Virgo network during the full third observing run (O3).
• Describe the methodology and statistical framework used to identify lensing-induced signatures in gravitational-wave signals.
• Report results and assess the presence of lensing signatures, including false-positive/false-alarm considerations and robustness checks.

Proposed method

• Apply gravitational-lensing search techniques to the full O3 dataset from LIGO–Virgo (and KAGRA collaboration inputs).
• Use a combination of lensing-informed signal analysis and statistical metrics (e.g., false-positive probability, false-alarm probability) to identify candidate signatures.
• Incorporate multi-band, template-based analyses and machine-learning approaches as part of the pipeline.
• Characterize signal-to-noise, power spectral density, and other signal-quality diagnostics to distinguish lensing effects from noise.

Experimental results

Research questions

• RQ1 Do gravitational-lensing signatures appear in the full O3 data from the LIGO–Virgo network?
• RQ2 What is the statistical significance of any candidate lensing signatures when accounting for false positives and false alarms?
• RQ3 How robust are potential lensing signatures to variations in detector noise and waveform modeling?
• RQ4 What constraints can be placed on lensing scenarios given the observed data and analysis pipeline?

Key findings

• The study reports results from a lensing-signature search across the full O3 observing run with the LIGO–Virgo network.
• The analysis employs statistical measures such as false-positive probability and false-alarm probability to evaluate candidate signatures.
• The methodology integrates template-based, multi-band, and possibly machine-learning components to assess lensing-related features in gravitational-wave signals.
• The paper discusses the robustness of findings against noise and instrument-induced artifacts as part of the evaluation.
• The results are presented within the context of the search framework and its sensitivity to lensing indications.