Multimessenger hierarchical triple merger gravitational-wave event pair GW190514-GW190521 inside AGN J124942.3 + 344929

Abstract

There is a candidate electromagnetic (EM) counterpart to the binary black hole merger GW190521, identified as ZTF19abanrhr within active galactic nuclei (AGN) J124942.3 + 344929. Additionally, GW190514 is proposed as a plausible precursor merger to GW190521 within a hierarchical merger scenario. In this study, we investigate the potential association between GW190514 and GW190521 as a hierarchical triple merger associated with ZTF19abanrhr, taking into account of the sky position, distance, and mass of the sources using a Bayesian criterion. Our analysis reveals that the association is favored over a random coincidence, with a log Bayes factor of 16.8, corresponding to an odds ratio of $\sim$$199:1$, assuming an astrophysical prior odds of $10^{-5}$. Notably, when accounting for the primary masses of the two gravitational-wave events as potential products of mergers in the AGN formation channel, the Bayes factor increases significantly, further enhancing the preference for this association by a factor of $\sim$$10^2$, corresponding to a log Bayes factor of 21.5 and an odds ratio of $\sim$$2\times10^4:1$. Our results suggest strong evidence for the first hierarchical triple merger associated with an EM counterpart in the AGN formation channel. This work is crucial for understanding the formation mechanisms of massive black holes, the role of AGNs in hierarchical mergers, and the implications of multimessenger astronomy.