TESS's First Bound Microlensing Planet: A Binary Microlensing Event Revealing a Planetary Companion toward the Galactic Plane

2026/07/02 by Mallory Harris, Diana Dragomir, Etienne Bachelet +2
Physics and Astronomy · #astro-ph.EP #astro-ph.GA

paper · pdf · doi:10.3847/2041-8213/ae7a50

published as ApJL 1005, L33 (2026) · 16 pages, 12 figures

arxiv created 2026/07/02 · arxiv updated 2026/08/06

Abstract

We report the discovery of Gaia23bra b, the first gravitationally bound microlensing planet detected by the Transiting Exoplanet Survey Satellite (TESS). Initially flagged as a single-lens event by the Gaia Science Alerts system, Gaia23bra was serendipitously observed by TESS over two consecutive sectors. During those TESS sectors, the light curve of the event displayed caustic-crossing features characteristic of a binary-lens event. Joint modeling of Gaia and TESS photometry with pyLIMA, supplemented by stellar parameter inference using pyLIMASS, suggests a K dwarf (M_L = 0.79^+0.19_-0.17 M_\odot) hosting a Jovian planet with M_P = 1.63_-0.38^+0.42 M_{\rm Jup} at a projected separation of a_⊥,min ≈ 4.8 AU. This result underscores the synergy between high-cadence photometry and long-baseline monitoring for robust microlensing characterization. Its location along the Galactic Plane highlights TESS's unexpected capacity for microlensing science through its all-sky coverage and its potential to detect planets in regions beyond the Galactic Bulge.

Citations

• Microlensing events indicate that super-Earth exoplanets are common in Jupiter-like orbits
• Estimating microlensing parameters from observables and stellar isochrones with pyLIMASS
• How Rare are TESS Free-Floating Planets?
• Searching for Free-Floating Planets with TESS: Results from Sectors 61-65
• Gaia22dkvLb: A Microlensing Planet Potentially Accessible to Radial-Velocity Characterization
• Four years of Type Ia Supernovae Observed by TESS: Early Time Light Curve Shapes and Constraints on Companion Interaction Models
• Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia EDR3 stars brighter than G=18.5
• Gaia Photometric Science Alerts
• Gaia Early Data Release 3: Photometric content and validation
• The Scientific Impact of the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) for Solar System Science
• Predictions of the Nancy Grace Roman Space Telescope Galactic Exoplanet Survey II: Free-Floating Planet Detection Rates
• Microlensing Optical Depth and Event Rate in the OGLE-IV Galactic Plane Fields
• An analysis of binary microlensing event OGLE-2015-BLG-0060
• OGLE-2018-BLG-0022: A Nearby M-dwarf Binary
• Predictions of the WFIRST Microlensing Survey I: Bound Planet Detection Rates
• Gaia Data Release 2: first stellar parameters from Apsis
• The Absolute Magnitude of the Sun in Several Filters
• pyLIMA : an open source package for microlensing modeling. I. presentation of the software and analysis on single lens models
• Korea Microlensing Telescope Network Microlensing Events from 2015: Event-Finding Algorithm, Vetting, and Photometry
• The Exoplanet Mass-Ratio Function from the MOA-II Survey: Discovery of a Break and Likely Peak at a Neptune Mass
• Limb and gravity-darkening coefficients for the TESS satellite at several metallicities, surface gravities, and microturbulent velocities
• On-orbit performance of the Gaia CCDs at L2
• TheGaiamission
• Campaign 9 of the K2 Mission: Observational Parameters, Scientific Drivers, and Community Involvement for a Simultaneous Space- and Ground-based Microlensing Survey
• Synthetic Stellar Photometry - I. General considerations and new transformations for broad-band systems
• The K2 Mission: Characterization and Early results
• emcee: The MCMC Hammer
• A systematic fitting scheme for caustic-crossing microlensing events
• First Space‐Based Microlens Parallax Measurement:SpitzerObservations of OGLE‐2005‐SMC‐001
• Microlensing optical depth towards the Galactic bulge from MOA observations during 2000 with Difference Image Analysis
• Simulation of a Space‐based Microlensing Survey for Terrestrial Extrasolar Planets
• The VizieR database of astronomical catalogues
• A method for optimal image subtraction
• Einstein Radii from Binary Lensing Events
• Theory of Pixel Lensing
• Finite Source Sizes and the Information Content of MACHO-Type Lens Search Light Curves