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

Abstract

We present the analysis of the microlensing event OGLE-2016-BLG-1227. The light curve of this short-duration 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, $t_{\mathrm{E}}\sim 3.5$ days, and the angular Einstein radius, ${\theta }_{\mathrm{E}}\sim 0.009$ mas, making the lens a candidate of a free-floating planet. Close inspection reveals that the 1L1S solution leaves small residuals with amplitude $\Delta I\lesssim 0.03$ 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 $M_{\mathrm{p}}=0.79_{-0.39}^{+1.30}{M}_{\mathrm{J}}$ and it is orbiting a low-mass host star with a mass of $M_{\mathrm{host}}=0.10_{-0.05}^{+0.17}{M}_{\odot }$ located with a projected separation of $a_{\perp }=3.4_{-1.0}^{+2.1}$ au. The planetary system is located in the Galactic bulge with a line-of-sight separation from the source star of $D_{\mathrm{LS}}=1.21_{-0.63}^{+0.96}$ 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.

arXiv comment8 figures, 4 tables

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