Natasha Abrams (UC Berkeley)

Gravitational microlensing provides a unique opportunity to probe the mass distribution and binary fraction of stars, black holes, and other objects in the Milky Way. Historically, microlensing events have been discovered primarily in the Galactic bulge by surveys designed solely for that purpose. As we enter the age of visible all-sky surveys, such as that of the Zwicky Transient Facility (ZTF) and Vera C. Rubin Observatory (Rubin), we gain the ability to probe microlensing events throughout the Galaxy. This allows us to analyze galactic structure and how the stellar and black hole mass functions vary across the Galaxy. I will present our analysis of optimal survey strategies, pipelines to discover microlensing events among a billion other lightcurves, and population simulations to physically interpret survey results. For Rubin, we have evaluated 360+ Operation Simulations to find their impact on microlensing discovery and characterization. Microlensing discovery efficiency is dominated by observing footprint, where more time spent looking at regions of high stellar density including the Galactic bulge, Galactic plane, and Magellanic clouds, leads to higher discovery and characterization rates. Additionally, we are developing filters to discover alerts in the incoming, real-time Rubin data. We also present a multiyear search for microlensing events with ZTF. We discovered 52 microlensing events in the 3 yrs of ZTF-I using the bulk lightcurves in the ZTF Public Data Release 5. 11 of our events are found outside of the Galactic plane (∣b∣ ≥ 10°), significantly increasing the number of previously discovered events in the stellar halo. To interpret these results we have improved our population simulation tool, PopSyCLE (Population Synthesis for Compact-object Lensing Events) to include binary objects which are typically neglected. Inclusion of binaries in PopSyCLE has brought simulated results into closer agreement with observations from the OGLE survey, and we find that > 50% of our simulated events include a binary lens or source system. Through this work we have shown that open-access, all-sky surveys will be powerful tools for probing galactic structure, binaries, and black holes through microlensing.