Microlensing Events in the Galactic Plane Using the Zwicky Transient Facility

Abstract

Microlensing is a powerful technique to study the Galactic population of "dark" objects such as exoplanets both bound and unbound, brown dwarfs, low-luminosity stars, old white dwarfs, neutron stars, and almost the only way to study isolated stellar-mass black holes. The majority of previous efforts to search for gravitational microlensing events have concentrated towards high-density fields such as the Galactic bulge. Microlensing events in the Galactic plane have the advantage of closer proximity and better constrained relative proper motions, leading to better constrained lens mass estimates at the expense of a lower optical depth compared to events towards the Galactic bulge. We use the Zwicky Transient Facility (ZTF) Data Release 5 (DR5) compiled from 2018--2021 to survey the Galactic plane in the region of $|b|<20^{\circ }$. We find a total of 60 candidate microlensing events including three that show a strong microlensing parallax effect. The rate of events traces Galactic structure, decreasing exponentially as a function Galactic longitude with scale length ${\ell }_0\sim 37^{\circ }$. On average, we find Einstein timescales of our microlensing events to be about three times as long ($\sim 60$ days) compared to those towards the Galactic bulge ($\sim 20$ days). This pilot project demonstrates that microlensing towards the Galactic plane shows strong promise for characterization of dark objects within the Galatic disk.

arXiv commentsubmitted to ApJ

References in corpus (25)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• The Zwicky Transient Facility: System Overview, Performance, and First Results
• The Zwicky Transient Facility: Data Processing, Products, and Archive
• The Zwicky Transient Facility: Science Objectives
• The Zwicky Transient Facility: Surveys and Scheduler
• No large population of unbound or wide-orbit Jupiter-mass planets
• Gravitational Microlensing in the Local Group
• Data analysis recipes: Using Markov Chain Monte Carlo
• The Zwicky Transient Facility: Observing System
• A Natural Formalism for Microlensing
• Experimental Limits on Primordial Black Hole Dark Matter from the First Two Years of Kepler Data
• Real-bogus classification for the Zwicky Transient Facility using deep learning
• MOA-cam3: a wide-field mosaic CCD camera for a gravitational microlensing survey in New Zealand
• Black Hole, Neutron Star and White Dwarf Candidates from Microlensing with OGLE-III
• Microlensing optical depth and event rate toward the Galactic bulge from 8 yr of OGLE-IV observations
• Modeling microlensing events with MulensModel
• Observation of Microlensing towards the Galactic Spiral Arms. EROS II 3 year survey
• On the accuracy of mass measurement for microlensing black holes as seen by Gaia and OGLE
• Year 1 of the ZTF high-cadence Galactic Plane Survey: Strategy, goals, and early results on new single-mode hot subdwarf B-star pulsators
• Prediction on detection and characterization of Galactic disk microlensing events by LSST
• Understanding EROS2 observations toward the spiral arms within a classical Galactic model framework
• Microlensing optical depth and event rate in the OGLE-IV Galactic plane fields
• A microlensing search of 700 million VVV light curves
• Gravitational microlensing events from the first year of the northern Galactic plane survey by the Zwicky Transient Facility
• Gravitational Microlensing Event Statistics for the Zwicky Transient Facility