Papers › GW190521 may be an intermediate mass ratio inspiral
GW190521 may be an intermediate mass ratio inspiral
Alexander H. Nitz, Collin D. Capano
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GW190521 is the first confident observation of a binary black hole merger with total mass M > 100 M_⊙. 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 m₁ˢʳᶜ = 168₋₆₁⁺¹⁵ M_⊙ and m₂ˢʳᶜ = 16₋₃⁺³³ M_⊙. The uniform in component-mass prior yields a bimodal posterior distribution. There is a low-mass-ratio mode (q<4) with m₁ˢʳᶜ = 100₋₁₈⁺¹⁷ M_⊙ and m₂ˢʳᶜ = 57₋₁₆⁺¹⁷ M_⊙ and a high-mass-ratio mode (q≥4) with m₁ˢʳᶜ = 166₋₃₅⁺¹⁶ M_⊙ and m₂ˢʳᶜ = 16₋₃⁺¹⁴ M_⊙. Although the two modes have nearly equal posterior probability, the maximum-likelihood parameters are in the high-mass ratio mode, with m₁ˢʳᶜ = 171 M_⊙ and m₂ˢʳᶜ = 16 M_⊙, and a signal-to-noise ratio of $16$. These results are consistent with the proposed "mass gap" produced by pair-instability in supernova. Our results differ from those published in Abbott et al. (2020b). 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 (ZTF). We report parameters assuming a common origin; however, the spatial agreement of GW190521 and the EM flare alone does not provide convincing evidence for the association (lnℬ ≳-4).
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