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

TL;DR

This paper analyzes a short-timescale microlensing event, revealing it is caused by a wide-separation planetary system rather than a free-floating planet, and estimates the planet's and host star's properties.

Contribution

It demonstrates that subtle deviations in microlensing light curves can reveal wide-separation planetary systems, not just free-floating planets.

Findings

The lens is a wide-separation planetary system with a planet of about 0.79 Jupiter masses.

The host star is a low-mass star around 0.10 solar masses.

The planetary system is located in the Galactic bulge at about 3.4 au from the host.

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, $t_{\rm E}\sim 3.5$ days, and the angular Einstein radius, $\theta_{\rm E}\sim 0.009$ 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 $M_{\rm p} = 0.79^{+1.30}_{-0.39} M_{\rm J}$ and it is orbiting a low-mass host star with a mass of $M_{\rm host}=0.10^{+0.17}_{-0.05} M_\odot$ located with a projected separation of $a_\perp=3.4^{+2.1}_{-1.0}$ au. The planetary system is located in the Galactic bulge with a line-of-sight separation from the source star of $D_{\rm LS}=1.21^{+0.96}_{-0.63}$ 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.