POEMMA-Balloon with Radio: Mission Overview

Abstract The Probe of Extreme Multi-Messenger Astrophysics (POEMMA) on a Balloon with Radio (PBR) is a planned instrument designed as a successor mission of EUSO-SPB2 and a prototype for a space-based mission such as POEMMA. The three primary science objectives are to make the first observations of Ultra-High-Energy Cosmic Rays (UHECR) from above using fluorescence light measurements, to measure high-altitude horizontal air-showers (HAHAs), and to search for Earth-skimming astrophysical neutrinos with PeV energies. To accomplish these goals, PBR will fly three main instruments. The Fluorescence Camera (FC) will measure the fluorescence light emission of UHECR-induced air-showers of ≳ EeV ranges energies from above. The Cherenkov Camera (CC) will observe Cherenkov light produced by above-the-limb cosmic rays with energies of ∼0.5 PeV as well as search for Earth-skimming neutrino signatures below the limb. Finally, PBR will fly a Radio Instrument (RI) consisting of two low-frequency sinuous radio antennas to measure radio signatures of HAHAs and Earth-skimming neutrino candidates both in individual trigger mode and utilizing the external triggers from the FC and CC. The FC and CC will be placed on the focal surface in a 1.1 m diameter aperture Schmidt optics telescope comprised of a 1.9 m×2 m primary mirror with a radius of curvature of 1.66 m. This telescope and the RI will be able to rotate in elevation angle from nadir to ∼ 12 ◦ above horizontal and 360 ◦ in azimuth to enable follow-up measurements of transient astrophysical sources of interest. The predicted sensitivity is expected to achieve instantaneous single source sensitivities similar to or exceeding current ground-based experiments at energies above ∼ 10 PeV. PBR will also fly an infrared camera to monitor cloud coverage and a gamma/x-ray particle detector to search for signals from cosmic ray air showers or other gamma-ray sources. The combination of these instruments makes PBR a unique experiment that is able to probe the physics of extensive air showers in ways currently inaccessible to ground-based detectors.