Multimessenger Constraints on LIGO/Virgo/KAGRA Gravitational-wave Binary Black Holes Merging in Active Galactic Nucleus Disks

Abstract While the LIGO/Virgo/KAGRA (LVK) gravitational-wave (GW) detectors have detected over 300 binary black hole (BBH) mergers to date, the first confirmation of an electromagnetic (EM) counterpart to such an event remains elusive. Previous works have performed searches for counterpart candidates in transient catalogs and have identified active galactic nucleus (AGN) flares coincident with GW events; existing theory predicts that such flares may arise from the interaction of the merger remnant with the embedding accretion disk environment. We apply a statistical formalism to measure the significance of coincidence for the catalog as a whole, measuring that less than 3% (90% credible interval) of LVK BBH mergers give rise to observable AGN flares. This result still allows up to ∼40% of BBH mergers to originate in AGN disks. We also examine the individual coincidences of each merger–flare pairing, determining that in all cases the flares are more likely to belong to a background population of flares not associated with GW events. Our results are consistent with theoretical predictions accounting for the observability of EM counterparts in AGN disks, as well as based on the fact that the most massive/luminous AGNs (such as those included in the search) are not expected to harbor the majority of the BBHs. We emphasize that developing both the means to distinguish BBH counterpart flares from background AGN flares and an understanding of which BBHs are most likely to produce AGN flares as counterparts is critical to optimizing the use of follow-up resources.