2021ApJ...907L...9N

GW190521 is the first confident observation of a binary black hole merger with total mass M> 100M_☉. Given the lack of observational constraints at these masses, we analyze GW190521 considering two different priors for the binary's masses: uniform in mass ratio and source-frame total mass, and uniform in source-frame component masses. For the uniform in mass-ratio prior, we find that the component masses are m₁^src=168_–61⁺¹⁵M_☉ and m₂^src=16_–3⁺³³M_☉. The uniform in component-mass prior yields a bimodal posterior distribution. There is a low-mass-ratio mode (q< 4) with m₁^src=100_–18⁺¹⁷M_☉ and m₂^src=57_–16⁺¹⁷M_☉ and a high-mass-ratio mode (q≥ 4) with m₁^src=166_–35⁺¹⁶M_☉ and m₂^src=16_–3⁺¹⁴M_☉. Although the two modes have nearly equal posterior probability, the maximum-likelihood parameters are in the high-mass-ratio mode, with m₁^src=171M_☉ and m₂^src=16M_☉, and a signal-to-noise ratio of 16. These results are consistent with the proposed "mass gap" produced by pair-instability in supernovae. Our results differ from those published in Abbott et al. We find that a combination of the prior used and the constraints applied may have prevented that analysis from sampling the high-mass-ratio mode. An accretion flare in AGN J124942.3+344929 was observed in possible coincidence with GW190521 by the Zwicky Transient Facility. We report parameters assuming a common origin; however, the spatial agreement of GW190521 and the electromagnetic flare alone does not provide convincing evidence for the association (ln B ≳-4).