GW190521 may be an intermediate mass ratio inspiral

Abstract

GW190521 is the first confident observation of a binary black hole merger with total mass $M>100{\mathrm{M}}_{\odot }$. 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 $m_1^{\mathrm{src}}=168_{-61}^{+15}{\mathrm{M}}_{\odot }$ and $m_2^{\mathrm{src}}=16_{-3}^{+33}{\mathrm{M}}_{\odot }$. The uniform in component-mass prior yields a bimodal posterior distribution. There is a low-mass-ratio mode ($q<4$) with $m_1^{\mathrm{src}}=100_{-18}^{+17}{\mathrm{M}}_{\odot }$ and $m_2^{\mathrm{src}}=57_{-16}^{+17}{\mathrm{M}}_{\odot }$ and a high-mass-ratio mode ($q\ge 4$) with $m_1^{\mathrm{src}}=166_{-35}^{+16}{\mathrm{M}}_{\odot }$ and $m_2^{\mathrm{src}}=16_{-3}^{+14}{\mathrm{M}}_{\odot }$. Although the two modes have nearly equal posterior probability, the maximum-likelihood parameters are in the high-mass ratio mode, with $m_1^{\mathrm{src}}=171M_{\odot }$ and $m_2^{\mathrm{src}}=16M_{\odot }$, 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 ($\ln \mathcal{B}\gtrsim -4$).

9 pages, 5 figures, 1 table, corresponding data release at http://github.com/gwastro/gw190521, updated to match version accepted by ApJL

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• Compact Binary Coalescences: Astrophysical Processes and Lessons Learned
• Gravitational wave of intermediate-mass black holes in Population III star clusters
• On the population III binary black hole mergers beyond the pair-instability mass gap
• Alternative possibility of GW190521: Gravitational waves from high-mass black hole-disk systems
• An optimized PyCBC search for gravitational waves from intermediate-mass black hole mergers
• Ancestral Black Holes of Binary Merger GW190521
• Interacting Kilonovae: Long-lasting Electromagnetic Counterparts to Binary Mergers in the Accretion Disks of Active Galactic Nuclei
• Observational limits on the rate of radiation-driven binary black hole capture events
• Spectroscopy for asymmetric binary black hole mergers
• Identification of Intermediate-mass Black Hole Candidates Among a Sample of Sd Galaxies