2020/07/24 by Liang Dai, Dai, Liang, Barak Zackay +7 · 1 citation
Physics and Astronomy · #Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences #Gamma-ray bursts and supernovae #General Relativity and Quantum Cosmology (gr-qc) #High Energy Astrophysical Phenomena (astro-ph.HE) #Pulsars and Gravitational Waves Research #Radio Astronomy Observations and Technology
paper · pdf · doi:10.48550/arxiv.2007.12709
openalex publication_date 2020/07/24 · openalex created_date 2020/07/29 · openalex updated_date 2026/07/28
We search for strongly lensed and multiply imaged gravitational wave signals in the second observing run of Advanced LIGO and Advanced Virgo (O2). We exploit a new source of information, the so-called Morse phase, which further mitigates the search background and constrains viable lenses. The best candidate we find is consistent with a strongly lensed signal from a massive binary black hole (BBH) merger, with three detected images consisting of the previously catalogued events GW170104 and GW170814, and a subthreshold trigger, GWC170620. Given the number of BBH events detected so far, we estimate an overall false alarm probability ∼ 10-4 for the observed high degree of parameter coincidence between the three events. On the flip side, we measure the Morse phase differences which suggest a complex and atypical lens system, with at least five images including a magnified image at a local maximum of the Fermat potential. The low prior probability for multiple lensed images and the amount of fine tuning required in the lens model reduce the credibility of the lensing hypothesis. The long time delays between lensed images point toward a galaxy cluster lens with an internal velocity dispersion σ∼ 650 \rm km/s, and the observed strain amplitudes imply a likely range 0.4 < z \lesssim 0.7 for the source redshift. We provide an error ellipse of ∼ 16 \rm deg2 for the sky location of the source together with additional specific constraints on the lens-host system, and encourage follow-up efforts to confirm or rule out any viable lens. If this is indeed a lensed event, successfully pinpointing the system would offer a unique opportunity to identify the host galaxy of a BBH merger, and even localize the source within it.