Microlensing Events in Five Years of Photometry from the Zwicky Transient Facility

Microlensing has a unique advantage for detecting dark objects in the Milky Way, such as free floating planets, neutron stars, and stellar-mass black holes. Most microlensing surveys focus towards the Galactic bulge, where higher stellar density leads to a higher event rate. However, microlensing events in the Galactic plane are closer, and take place over longer timescales. This enables a better measurement of the microlensing parallax, which serves as an independent constraint on the mass of the dark lens. In this work, we systematically searched for microlensing events in Zwicky Transient Facility (ZTF) Data Release 17 from 2018--2023 in the Galactic plane region $|b| < 20^\circ$. We find 124 high-confidence microlensing events and 54 possible events. In the event selection, we use the efficient \texttt{EventFinder} algorithm to detect microlensing signals, which could be used for large datasets such as future ZTF data releases or data from the Rubin Observatory Legacy Survey of Space and Time (LSST). With detection efficiencies of ZTF fields from catalog-level simulations, we calculate the mean Einstein timescale to be $\langle t_\mathrm{E}\rangle = 51.7 \pm 3.3$ days, smaller than previous results of the Galactic plane to within 1.5-$\sigma$. We calculate optical depths and event rates, which we interpret with caution due to the use of visual inspection in creating our final sample. With two years of additional ZTF data in DR17, we have more than doubled the amount of microlensing events (60) found in the three-year DR5 search and found events with longer Einstein timescales than before.