The Microlensing Event Rate and Optical Depth from MOA-II 9 Yr Survey Toward the Galactic Bulge

Nunota, Kansuke; Sumi, Takahiro; Koshimoto, Naoki; Rattenbury, Nicholas J.; Abe, Fumio; Barry, Richard; Bennett, David P.; Bhattacharya, Aparna; Fukui, Akihiko; Hamada, Ryusei; Hamada, Shunya; Hamasaki, Naoto; Hirao, Yuki; Silva, Stela Ishitani; Itow, Yoshitaka; Matsubara, Yutaka; Miyazaki, Shota; Muraki, Yasushi; Nagai, Tsutsumi; Olmschenk, Greg; Ranc, Clement; Satoh, Yuki K.; Suzuki, Daisuke; Tristram, Paul. J.; Vandorou, Aikaterini; Yama, Hibiki; (MOA collaboration)
Bibliographical reference

The Astrophysical Journal

Advertised on:
2
2025
Number of authors
27
IAC number of authors
1
Citations
0
Refereed citations
0
Description
We present measurements of the microlensing optical depth and event rate toward the Galactic bulge using the data set from the 2006 to 2014 MOA-II survey, which covers 22 bulge fields spanning ∼42 deg2 between ‑5° < l < 10° and ‑7° < b < ‑1°. In the central region with ∣l∣ < 5°, we estimate an optical depth of and an event rate of Γ = [16.08 ± 0.28] × 10‑6 using a sample consisting of 3525 microlensing events, with Einstein radius crossing times of tE < 760 days and a source star magnitude of Is < 21.4 mag. We confirm our results are consistent with the latest measurements from the OGLE-IV 8 yr data set. We find our result is inconsistent with a prediction based on Galactic models, especially in the central region with ∣b∣ < 3°. These results can be used to improve the Galactic bulge model, and more central regions can be further elucidated by upcoming microlensing experiments, such as the PRime-focus Infrared Microlensing Experiment and Nancy Grace Roman Space Telescope.