Historic microlensing events in the euclid Galactic Bulge Survey

TL;DR

This work targets historical microlensing events in the Euclid Galactic Bulge Survey footprint to maximize the scientific return of lens–source resolution. It builds a uniform catalog of 8081 events from OGLE, MOA, and KMTNet up to 2023, re-models them to extract $t_E$, $I_{ m base}$, and $\pi_E$ where possible, and pairs these with a fast Galactic model to produce posterior lens–source proper-motion distributions. By propagating these motions to the EGBS epoch, the authors compute probabilities that the lens and source are separated beyond several angular thresholds, effectively ranking events by their lens-detection prospects; they also compile known planetary events and report their predicted separations. The resulting HistoricList, including 51 planetary events and public accessibility via GitHub, provides a practical guide for selecting high-priority targets for Euclid (and Romans) follow-up, enabling improved mass/distance inferences and bulge tomography. This catalog thus bridges ground-based microlensing history with future space-based capabilities, highlighting a path toward robust 3D mapping of the Galactic bulge.

Abstract

Microlensing campaigns have a long history of observations covering the Galactic bulge, where thousands of detections have been obtained, including many exoplanetary systems. The Euclid Galactic Bulge Survey represents a unique opportunity to revisit a large number of past events and attempt the lens-source resolution of known events falling in the covered area. As the analysis of individual events requires non-negligible efforts, it is important to establish priorities among all possible targets, identifying those candidates with the higher chance for a successful resolution of the lens from the source and with the highest scientific interest. Drawing from the databases of the three main microlensing surveys (OGLE, MOA and KMTNet), we compile the complete catalog of past microlensing events in the Euclid survey footprint up to year 2023, containing 8081 entries. By re-modeling all events and cross-checking with Galactic models, we estimate the relative lens-source proper motions for all events. Taking into account all uncertainties, for each microlensing event we are able to estimate the probability that the lens is separated from the source by more than a given angular distance threshold. Hence, we rank all events by their resolution probability, providing additional useful information that will guide future analyses on the most promising candidates. A particular attention is dedicated to known planetary microlensing events.

Figures (12)

• Figure 1: Outline of the nine Euclid Galactic Bulge Survey pointings (red) overlaid on a Gaia image of the Milky Way. The total outlined sky coverage is 4.8 deg$^2$.
• Figure 2: Fields observed in the EGBS. For each field four different dithers are visible. All historic microlensing events falling in the EGBS are shown in green. In particular, published planetary microlensing events are shown in red.
• Figure 3: Distribution of events per survey. Some events have been observed by more than one survey.
• Figure 4: Distribution of events per year.
• Figure 5: Distribution of events in terms of the $\chi^2/d.o.f.$. achieved in their fit.