A next-generation ground array for ultrahigh-energy cosmic rays: Fluorescence detector Array of Single-pixel Telescopes (FAST)
The origin and nature of ultrahigh-energy cosmic rays (UHECRs) are one of the most intriguing mysteries in Astroparticle Physics. The two giant observatories, Telescope Array Experiment and Pierre Auger Observatory, are steadily observing UHECRs in both hemispheres. We highlight their latest results and address the requirements for a next-generation observatory. The Fluorescence detector Array of Single-pixel Telescopes (FAST) is a design concept for the next-generation of UHECR observatories, addressing the requirements for a large-area, low-cost detector suitable for measuring the properties of the highest energy cosmic rays with an unprecedented aperture. We have developed a full-scale prototype consisting of four 200 mm photomultiplier-tubes at the focus of a segmented mirror of 1.6 m in diameter. In October 2016 and September 2017, we installed two full-scale prototypes at the Telescope Array site in central Utah, USA, and began steady data taking. We report on preliminary results of the full-scale FAST prototypes, including measurements of artificial light sources, distant ultraviolet lasers, and UHECRs, and discuss future perspectives.