The Extreme Universe Space Observatory on a Super Pressure Balloon 2 (EUSO-SPB2), successfully launched from Wanaka, New Zealand on May 13, 2022, is a precursor for a space-based astroparticle observatory such as the Probe Of Extreme Multi-Messenger Astrophysics (POEMMA). EUSO-SPB2 flew two custom telescopes. Both have UV/UV-visible sensitivity and feature Schmidt optics. The Fluorescence Telescope (FT) measures ultra-high energy cosmic rays by looking down. The \v{C}erenkov Telescope (CT) searches for neutrino signatures by looking toward Earth's limb. The two telescopes each have a 1 m diameter entrance pupil and segmented glass mirrors that collect light from extensive air showers at the PeV and EeV-scale. Here we describe the FT telescope optics together with the results of the FT field tests at the Utah Telescope Array (TA) site from August/September 2022. The FT recorded the night sky background, lasers, and artificial point sources. The field tests included an absolute photometric calibration of the FT telescope that is compared to a piece-wise laboratory calibration.
@article{arxiv.2310.06209,
title = {EUSO-SPB2 Fluorescence Telescope Calibration and Field Tests},
author = {Viktoria Kungel and Matteo Battisti and George Filippatos and Tobias Heibges and Evgeny Kuznetsov and Marco Mese and Stephan S. Meyer and Etienne Parizot and Valentina Scotti and Patrick Sternberg and Lawrence Wiencke},
journal= {arXiv preprint arXiv:2310.06209},
year = {2023}
}