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 $t_{\mathrm{E}}\sim 7.5$ days. The Einstein radius is unusually small, ${\theta }_{\mathrm{E}}=0.065$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 $(M_{\mathrm{host}},M_{\mathrm{planet}})=(46_{-25}^{+79},0.75_{-0.40}^{+1.26})M_{\mathrm{J}}$ and source-lens distance $D_{\mathrm{LS}}=0.99_{-0.54}^{+0.91}\mathrm{kpc}$, 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 $\mu =3.2\pm 0.5\mathrm{mas}\mathrm{y}{\mathrm{r}}^{-1}$. The projected companion-host separation is $0.59_{-0.11}^{+0.12}\mathrm{AU}$, indicating that the planet is placed beyond the snow line of the host, i.e., $a_{sl}\sim 0.12\mathrm{AU}$. Planet formation scenarios combined with the small companion-host mass ratio $q\sim 0.016$ 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.

20 pages, 6 figures