On-sky performance of RIMAS: rapid infrared imager spectrometer

Abstract

In this age of multi-messenger astronomy precipitated by GW 170817, it is important to have instruments throughout the EM spectrum performing follow-up observations. The Rapid infrared IMAger Spectrometer (RIMAS) is designed to observe transient events within minutes of the initial detection. RIMAS is a NIR imager spectrometer (R≈25, 250 and 5000) designed to observe afterglows of high-redshift GRBs in the Y, J, H and K bands. Commissioned in June 2025, RIMAS is installed on the 4.3 m Lowell Discovery Telescope located outside Flagstaff, AZ, and is now continuously available for Target of Opportunity observations. RIMAS’s high resolution spectrograph is enabled by the first instance of ruled grisms used in cross-dispersed mode for ground based NIR astronomy, and is also the first instrument to use Roman Space Telescope package H4RG-10 detectors for spectroscopic measurements of astronomical objects. Here, we explore the on-sky performance of RIMAS after 10 months of operations.