When travelling from their source to the observer, gravitational waves can get deflected by massive objects along their travel path. For a massive lens and a good source-lens alignment, the wave undergoes strong lensing, leading to several images with the same frequency evolution. These images are separated in time, magnified, and can undergo an overall phase shift. Searches for strongly lensed gravitational waves look for events with similar masses, spins, and sky location and linked through so-called lensing parameters. However, the agreement between these quantities can also happen by chance. To reduce the overlap between background and foreground, one can include lensing models. When doing realistic searches, one does not know which model is the correct one to be used. Using an incorrect model could lead to the non-detection of genuinely lensed events. In this work, we investigate how one can reduce the false alarm probability when searching for strongly lensed events. We focus on the impact of the addition of a model for the lens density profile and investigate the effect of potential errors in the modelling. We show that the risks of false alarm are high without the addition of a lens model. We also show that slight variations in the profile of the lens model are tolerable, but a model with an incorrect assumption about the underlying lens population causes significant errors in the identification process. We also suggest some strategies to improve confidence in the detection of strongly lensed gravitational waves.
Owing to the forecasted improved sensitivity of ground-based gravitational-wave detectors, new research avenues will become accessible. This is the case for gravitational-wave strong lensing, predicted with a non-negligible observation rate in the coming years. However, because one needs to investigate all the event pairs in the data, searches for strongly lensed gravitational waves are often computationally heavy, and one faces high false-alarm rates. In this paper, we present upgrades made to the golum software, making it more reliable while increasing its speed by re-casting the look-up table, imposing a sample control, and implementing symmetric runs on the two lensed images. We show how the recovered posteriors have improved coverage of the parameter space and how we increase the pipeline’s stability. Finally, we show the results obtained by performing a joint analysis of all the events reported until the GWTC-3 catalogue, finding similar conclusions to the ones presented in the literature.
more » « less- NSF-PAR ID:
- 10468410
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 526
- Issue:
- 2
- ISSN:
- 0035-8711
- Format(s):
- Medium: X Size: p. 3088-3098
- Size(s):
- ["p. 3088-3098"]
- Sponsoring Org:
- National Science Foundation
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