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

Abstract

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 and source-lens distance , 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 , 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.