POEMMA-Balloon with Radio: A multi-messenger, multi-detector balloon payload

TL;DR

POEMMA-Balloon with Radio (PBR) is a compact, balloon-based precursor to a POEMMA-like space observatory designed to validate space-based fluorescence detection, perform first simultaneous optical Cherenkov and radio measurements of high-altitude horizontal air-showers, and enable targeted very-high-energy neutrino searches. It combines a wide-field Schmidt telescope with a hybrid focal surface (Cherenkov camera and fluorescence camera) plus a dedicated radio instrument and an X-/gamma-ray detector, all integrated on a 1.1 m aperture system and deployed on a Super-Pressure Balloon from Wanaka for 20+ days. The mission aims to validate detection strategies from suborbital altitudes, quantify composition-sensitive shower development near the knee region, and enable rapid ToO follow-ups for multi-messenger neutrinos, while delivering a large, multi-hybrid data set to inform future space missions. Techically, PBR advances subsystems toward POEMMA-like TRL6, leveraging lessons from EUSO-SPB2 and PUEO, and demonstrates the integrated performance of a hybrid focal surface, advanced SiPM/MAPMT cameras, a radio-detection chain, and a compact X-/gamma-ray detector in a near-space environment. The project thus serves as a critical intermediate step to maximize exposure at the highest energies and to strengthen multi-messenger astrophysics capabilities for the next generation of UHECR experiments.

Abstract

A review of the current status of the field of Ultra-High-Energy Cosmic Ray (UHECR) including a summary of remaining open questions was presented in the white paper "Ultra-High Energy Cosmic Rays: at the Intersection of the Cosmic and Energy Frontiers" (Astropart. Phys. 147 (2023) 102794; arXiv:2205.05845). The authors concluded that two types of next-generation detectors are needed to answer these questions: high-accuracy instruments and detectors that maximize exposure at the highest energies. The Probe Of Extreme Multi-Messenger Astrophysics (POEMMA), a proposed dual-satellite observatory, exemplifies the latter class and is designed to increase statistics of the highest-energy cosmic rays and to detect very-high-energy neutrinos following multi-messenger alerts. POEMMA-Balloon with Radio (PBR) implements a compact, balloon-borne version of the POEMMA concept, adapted for a Super-Pressure Balloon flight from Wanaka, New Zealand, with an expected campaign exceeding 20 days. PBR couples a wide field-of-view Schmidt telescope and a hybrid optical focal surface with a dedicated radio instrument to deliver simultaneous, complementary measurements of extensive air showers. The mission will validate the fluorescence detection strategy from space and raise technology readiness for a POEMMA-like space mission by observing UHECR-induced fluorescence light from suborbital altitudes, obtaining the first simultaneous optical Cherenkov and radio observations of high-altitude horizontal air showers above the cosmic-ray knee (E>3PeV), enabling energy-spectrum and composition studies at the PeV scale, and performing follow-ups of multi-messenger alerts to search for very-high-energy neutrinos via upward-going air showers. This paper summarizes the PBR payload and its expected performance.

Figures (22)

• Figure 1: Main PBR scientific goals: observation of UHECRs via fluorescence from above; study a large set of HAHAs; search for astrophysical neutrinos from multi-messenger targets of opportunity.
• Figure 2: Left: HAHA trajectories with different inclination angles, $\theta_{d}$, relative to PBR nadir position at an altitude of $h$ above the Earth. $\theta_{E}$ corresponds to the Earth-centric angle of the HAHA trajectory, assuming the top of the atmsophere to be at $z_{\mathrm{atm}}$. Right: Altitude profile versus traversed atmospheric grammage for the $\theta_{d}$ as shown on the left.
• Figure 3: Left: Early longitudinal development of 100 HAHAs induced by 3 PeV proton and iron primaries, as simulated with CORSIKA (COsmic Ray Simulations for KAscade) Heck:1998vt. Right: On-axis Cherenkov intensities $\Psi$ at payload for showers in the left panel with an arrival angle $\theta_{d} = 89.5^{\circ}$.
• Figure 4: The PBR payload.
• Figure 5: Optical sketch of the PBR modified Schmidt telescope, showing all major components.