2017/12/31 by Przemek Mroz, Y. -H. Ryu, J. Skowron +26 · 1 citation
Physics and Astronomy · #astro-ph.EP
paper · pdf · doi:10.3847/1538-3881/aaaae9
published as AJ 155, 121 (2018) · accepted to AJ
arxiv created 2018/02/13 · arxiv updated 2018/02/22
Current microlensing surveys are sensitive to free-floating planets down to Earth-mass objects. All published microlensing events attributed to unbound planets were identified based on their short timescale (below two days), but lacked an angular Einstein radius measurement (and hence lacked a significant constraint on the lens mass). Here, we present the discovery of a Neptune-mass free-floating planet candidate in the ultrashort (t\rm E=0.320±0.003 days) microlensing event OGLE-2016-BLG-1540. The event exhibited strong finite-source effects, which allowed us to measure its angular Einstein radius of θ\rm E=9.2±0.5 μas. There remains, however, a degeneracy between the lens mass and distance. The combination of the source proper motion and source-lens relative proper motion measurements favors a Neptune-mass lens located in the Galactic disk. However, we cannot rule out that the lens is a Saturn-mass object belonging to the bulge population. We exclude stellar companions up to 15 au.