GW190521: A binary black hole merger inside an active galactic nucleus?
S. Morton, S. Rinaldi, Alejandro Torres-Orjuela, Andrea Derdzinski, Maria Paola Vaccaro, W. Del Pozzo
Abstract
GW190521, the most massive binary black hole merger confidently detected by the LIGO-Virgo-KAGRA Collaboration, is the first gravitational-wave observation of an intermediate-mass black hole. The signal was followed approximately 34 days later by flare ZTF19abanrhr, detected in AGN $\mathrm{J}124942.3+344929$ by the Zwicky Transient Facility at the 78% spatial contour for GW190521's sky localization. Using the GWTC-2.1 data release, we find that the association between GW190521 and flare ZTF19abanrhr as its electromagnetic counterpart is preferred over a random coincidence of the two transients with a log Bayes' factor of 8.6, corresponding to an odds ratio of $\ensuremath{\sim}5400:1$ for equal prior odds and $\ensuremath{\sim}400:1$ assuming an astrophysical prior odds of $1/13$. Given the association, the multimessenger signal allows for an estimation of the Hubble constant, finding ${H}_{0}=10{2}_{\ensuremath{-}25}^{+27}\text{ }\text{ }\mathrm{km}\text{ }{\mathrm{s}}^{\ensuremath{-}1}\text{ }{\mathrm{Mpc}}^{\ensuremath{-}1}$ when solely analyzing GW190521 and ${79.2}_{\ensuremath{-}9.6}^{+17.6}\text{ }\text{ }\mathrm{km}\text{ }{\mathrm{s}}^{\ensuremath{-}1}\text{ }{\mathrm{Mpc}}^{\ensuremath{-}1}$ assuming prior information from the binary neutron star merger GW170817, both consistent with the existing literature.