EUSO-SPB2 Fluorescence Telescope Calibration and Field Tests

TL;DR

The paper details the calibration and field testing of the EUSO-SPB2 Fluorescence Telescope, a key component in ultra-high energy cosmic ray detection, including optical setup and calibration results from field tests.

Contribution

It presents the design, calibration, and field test results of the EUSO-SPB2 Fluorescence Telescope, advancing space-based cosmic ray observation technology.

Findings

Successful absolute photometric calibration achieved

Effective detection of night sky background and artificial sources

Field tests validated telescope optical performance

Abstract

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.