标题： HST 之前成像的自由漂浮行星候选者微透镜事件 显示英文标题

标题： HST pre-imaging of a free-floating planet candidate microlensing event

摘要： 高频率的微透镜观测揭示了一类非常短时标微透镜事件，这些事件被认为是由银河系中游荡的自由漂浮行星（FFP）群体引起的。 不幸的是，这类事件的光变曲线与宽轨道行星引起的光变曲线无法区分。 为了正确区分这两种情况，需要高分辨率的观测，以便在事件发生前或发生后很久之前就能分辨出透镜可能的发光伴星。 通常，事件与高分辨率观测之间的基线需要相当长（$\sim 10$年），这阻碍了潜在的后续观测。 然而，如果存在存档数据，就有可能加以利用。 在这里，我们介绍了微透镜事件OGLE-2023-BLG-0524的分析，该事件的位置于1997年被哈勃空间望远镜（HST）捕捉到。 因此，我们实现了创纪录的25年的基线长度。 事件持续时间非常短（$t_E = 0.346 \pm 0.008$天），表明FFP是合理的解释。 我们没有在HST数据中检测到透镜的潜在伴星，这与事件的FFP起源一致。 由于有可用的HST数据，我们能够根据假设的群体模型，从25%到48%之间排除潜在的恒星伴星。 基于光变曲线中的有限源效应，我们测得了角爱因斯坦半径值$\theta_E = 4.78 \pm 0.23 \mu as$，这表明银河系盘中可能存在一个超级地球，或者银河系核球中可能存在一个亚土星质量的行星。 我们表明，存档的高分辨率图像应适用于多个微透镜事件，使我们有机会以前所未有的方式看到事件发生多年前的透镜系统。 显示英文摘要

摘要： High-cadence microlensing observations uncovered a population of very short-timescale microlensing events, which are believed to be caused by the population of free-floating planets (FFP) roaming the Milky Way. Unfortunately, the light curves of such events are indistinguishable from those caused by wide-orbit planets. To properly differentiate both cases, one needs high-resolution observations that would allow resolving a putative luminous companion to the lens long before or after the event. Usually, the baseline between the event and high-resolution observations needs to be quite long ($\sim 10$ yr), hindering potential follow-up efforts. However, there is a chance to use archival data if they exist. Here, we present an analysis of the microlensing event OGLE-2023-BLG-0524, the site of which was captured in 1997 with the Hubble Space Telescope (HST). Hence, we achieve a record-breaking baseline length of 25 years. A very short duration of the event ($t_E = 0.346 \pm 0.008$ d) indicates an FFP as the explanation. We have not detected any potential companion to the lens with the HST data, which is consistent with the FFP origin of the event. Thanks to the available HST data, we are able to reject from 25% to 48% of potential stellar companions depending on the assumed population model. Based on the finite-source effects in the light curve we measure the angular Einstein radius value $\theta_E = 4.78 \pm 0.23 \mu as$, suggesting a super-Earth in the Galactic disk or a sub-Saturn-mass planet in the Galactic bulge. We show that the archival high-resolution images should be available for several microlensing events, providing us with the unprecedented possibility of seeing the lensing system as it was many years before the event.