OGLE-2017-BLG-1522: A Giant Planet around a Brown Dwarf Located in the Galactic Bulge

We report the discovery of a giant planet in the OGLE-2017-BLG-1522 microlensing event. The planetary perturbations were clearly identified by high-cadence survey experiments despite the relatively short event timescale of t _E ∼ 7.5 days. The Einstein radius is unusually small, θ _E = 0.065 mas, implying that the lens system either has very low mass or lies much closer to the microlensed source than the Sun, or both. A Bayesian analysis yields component masses ({M}_host},{M}_planet})=({46}_-25⁺⁷⁹,{0.75}_-0.40^+1.26) {M}_{{J}} and source-lens distance {D}_LS}={0.99}_-0.54^+0.91 {kpc}, implying that this is a brown-dwarf/Jupiter system that probably lies in the Galactic bulge, a location that is also consistent with the relatively low lens-source relative proper motion μ = 3.2 ± 0.5 mas yr^-1. The projected companion-host separation is {0.59}_-0.11^+0.12 {au}, indicating that the planet is placed beyond the snow line of the host, i.e., a _sl ∼ 0.12 au. Planet formation scenarios combined with the small companion-host mass ratio q ∼ 0.016 and separation suggest that the companion could be the first discovery of a giant planet that formed in a protoplanetary disk around a brown-dwarf host.