Development of UV telescope system for the astronomical observation satellite PETREL

PETREL (Platform for Extra & Terrestrial Remote Examination with LCTF) is a 50kg class satellite with a 80mm-diameter Ultraviolet Telescope (UVT). The science missions of the UVT system are the discovery of high-energy transients, such as supernovae and gravitational-wave electromagnetic sources. To achieve them, the optical system is optimized to detect near-UV photons between 250 and 300 nm. Within a 30-minutes exposure time per every revolution, it surveys a remarkably wide field as 50 deg^2 with a high sensitivity of 20~ AB magnitude. The Board Unit has an on-board computer, which directly analyzes raw images obtained by a back-illuminated CMOS sensor. The computer can detect transients immediately, so as to alert the transient information to ground within 30 minutes of discovery. We will achieve the first UV survey to explore the transients in their early phase and reveal the underlying physical processes.