The Prime Focus Infrared Microlensing Experiment (PRIME): First Results
Abstract
We present the description of the instruments and the first results of the PRime-focus Infrared Microlensing Experiment (PRIME). PRIME is the first dedicated near-infrared (NIR) microlensing survey telescope located at the South African Astronomical Observatory (SAAO) in Sutherland, South Africa. Among its class, it offers one of the widest fields of view in the NIR regime. PRIME's main goals are (1) To study planetary formation by measuring the frequency and mass function of planets. In particular, we compare results from the central Galactic bulge (GB), accessible only in the NIR by PRIME, with those from the outer GB by optical surveys. (2) To conduct concurrent observations with NASA's Nancy Grace Roman Space telescope. Due to the different lines of sight between the ground and space, we detect slight variations in light curves, known as ``Space-based parallax." This effect allows us to measure the mass of lens systems and their distance from the Earth. It is the only method to measure the mass of the free-floating planets down to Earth-mass. We began the GB survey in February 2024 and analyzed images through June 1, 2025, identifying 486 microlensing candidates and over a thousand variable stars, including Mira variables, which are useful to study the Galactic structure. We issue real-time alerts for follow-up observations, supporting exoplanet searches, and the chemical evolution studies in the GB. During the off-bulge season, we conduct an all-sky grid survey and Target of Opportunity (ToO) observations of transients, including gravitational wave events, gamma-ray bursts, and other science.
Keywords
Cite
@article{arxiv.2508.14474,
title = {The Prime Focus Infrared Microlensing Experiment (PRIME): First Results},
author = {Takahiro Sumi and David A. H. Buckley and Alexander S. Kutyrev and Motohide Tamura and David P. Bennett and Ian A. Bond and Giuseppe Cataldo and Joseph M. Durbak and S. Bradley Cenko and Dale Fixsen and Orion Guiffreda and Ryusei Hamada and Yuki Hirao and Asahi Idei and Dan Kelly and Markus Loose and Gennadiy N. Lotkin and Eric I. Lyness and Stephen Maher and Shuma Makida and Noriyuki Matsunaga and Shota Miyazaki and Gregory Mosby and Samuel H. Moseley and Tutumi Nagai and Togo Nagano and Seiya Nakayama and Mayu Nishio and Kansuke Nunota and Ryo Ogawa and Ryunosuke Oishi and Yui Okumoto and Nicholas J. Rattenbury and Yuki K. Satoh and Elmer H. Sharp and Daisuke Suzuki and Takuto Tamaoki and Eleonora Troja and Sarah V. White and Hibiki Yama},
journal= {arXiv preprint arXiv:2508.14474},
year = {2025}
}
Comments
16 pages, 15 figures, published in the Astronomical Journal