OGLE-2016-BLG-0263Lb: Microlensing Detection of a Very Low-mass Binary Companion through a Repeating Event Channel

We report the discovery of a planet-mass companion to the microlens OGLE-2016-BLG-0263L. Unlike most lowmass companions that were detected through perturbations to the smooth and symmetric light curves produced by the primary, the companion was discovered through the channel of a repeating event, in which the companion itself produced its own single-mass light curve after the event produced by the primary had ended. Thanks to the continuous coverage of the second peak by high-cadence surveys, the possibility of the repeating nature due to source binarity is excluded with a 96% confidence level. The mass of the companion estimated by a Bayesian analysis is M p 4.1 -2.5 +6.5 M J . The projected primary-companion separation is α ⊥ = 6.5 1.9 1.3 au. The ratio of the separation to the snow-line distance of α ⊥ a sl ∼ ∼15.4 corresponds to the region beyond Neptune, the outermost planet of the solar system. We discuss the importance of high-cadence surveys in expanding the range of microlensing detections of low-mass companions and future space-based microlensing surveys.