OGLE-2016-BLG-1227L: A Wide-separation Planet from a Very Short-timescale Microlensing Event (original) (raw)

We present the analysis of the microlensing event OGLE-2016-BLG-1227. The light curve of this shortduration event appears to be a single-lens event affected by severe finite-source effects. Analysis of the light curve based on single-lens single-source (1L1S) modeling yields very small values of the event timescale, t E ∼ 3.5 days, and the angular Einstein radius, θ E ∼ 0.009 mas, making the lens a candidate of a free-floating planet. Close inspection reveals that the 1L1S solution leaves small residuals with amplitude ∆I 0.03 mag. We find that the residuals are explained by the existence of an additional widely-separated heavier lens component, indicating that the lens is a wide-separation planetary system rather than a free-floating planet. From Bayesian analysis, it is estimated that the planet has a mass of M p = 0.79 +1.30 −0.39 M J and it is orbiting a low-mass host star with a mass of M host = 0.10 +0.17 −0.05 M ⊙ located with a projected separation of a ⊥ = 3.4 +2.1 −1.0 au. The planetary system is located in the Galactic bulge with a line-of-sight separation from the source star of D LS = 1.21 +0.96 −0.63 kpc. The event shows that there are a range of deviations in the signatures of host stars for apparently isolated planetary lensing events and that it is possible to identify a host even when a deviation is subtle.