60 Microlensing Events from the Three Years of Zwicky Transient Facility Phase One

TL;DR

This paper presents the first multi-year search for microlensing events using ZTF data, discovering 60 high-quality events and identifying many more candidates, demonstrating scalable methods for future large surveys.

Contribution

It introduces a scalable, efficient method for detecting microlensing events in all-sky survey data, expanding the known events especially outside the Galactic plane.

Findings

Discovered 60 high-quality microlensing events in three years of ZTF data.

Nearly doubled the number of known stellar halo microlensing events outside the Galactic plane.

Identified 1,558 ongoing candidate events for future observation.

Abstract

Microlensing events have historically been discovered throughout the Galactic bulge and plane by surveys designed solely for that purpose. We conduct the first multi-year search for microlensing events on the Zwicky Transient Facility (ZTF), an all-sky optical synoptic survey that observes the entire visible Northern sky every few nights. We discover 60 high quality microlensing events in the three years of ZTF-I using the bulk lightcurves in the ZTF Public Data Release 5. 19 of our events are found outside of the Galactic plane ($|b| \geq 15^\circ$), nearly doubling the number of previously discovered events in the stellar halo from surveys pointed toward the Magellanic Clouds and the Andromeda Galaxy. We also record 1,558 ongoing candidate events as potential microlensing that can continue to be observed by ZTF-II for identification. The scalable and computationally efficient methods developed in this work can be applied to future synoptic surveys, such as the Vera C. Rubin Observatory's Legacy Survey of Space and Time and the Nancy Grace Roman Space Telescope, as they attempt to find microlensing events in even larger and deeper datasets.