High-cadence observations of the Galactic bulge by the microlensing surveys led to the discovery of a handful of extremely short-timescale microlensing events that can be attributed to free-floating or wide-orbit planets. Here, we report the discovery of another strong free-floating planet candidate, which was found from the analysis of the gravitational microlensing event OGLE-2019-BLG-0551. The light curve of the event is characterized by a very short duration (<3 d) and a very small amplitude (< 0.1 mag). From modeling of the light curve, we find that the Einstein timescale, tE = 0.381 +/- 0.017 d, is much shorter, and the angular Einstein radius, thetaE = 4.35 +/- 0.34 uas, is much smaller than those of typical lensing events produced by stellar-mass lenses (tE ~ 20 d, thetaE ~ 0.3 mas), indicating that the lens is very likely to be a planetary-mass object. We conduct an extensive search for possible signatures of a companion star in the light curve of the event, finding no significant evidence for the putative host star. For the first time, we also demonstrate that the angular Einstein radius of the lens does not depend on blending in the low-magnification events with strong finite source effects.

中文翻译：

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微透镜事件中的自由漂浮或宽轨道行星 OGLE-2019-BLG-0551

通过微透镜巡天对银河隆起的高节奏观测导致发现了少数极短时间尺度的微透镜事件，这些事件可归因于自由漂浮或宽轨道行星。在这里，我们报告发现了另一个强大的自由漂浮行星候选者，它是通过对引力微透镜事件 OGLE-2019-BLG-0551 的分析发现的。该事件的光变曲线的特点是持续时间很短（<3 d）和幅度很小（< 0.1 mag）。从光变曲线的建模中，我们发现爱因斯坦时间尺度 tE = 0.381 +/- 0.017 d 更短，并且角爱因斯坦半径 thetaE = 4.35 +/- 0.34 uas 远小于典型透镜的那些恒星质量透镜产生的事件（tE ~ 20 d，thetaE ~ 0.3 mas），表明镜头很可能是一个行星质量的物体。我们在事件的光变曲线中对伴星的可能特征进行了广泛的搜索，但没有发现推定的主星存在的重要证据。我们还首次证明，透镜的爱因斯坦角半径不依赖于低放大率事件与强有限源效应的混合。