Development of PANOSETI Telescopes for Ultra-High-Energy Gamma-Ray Astronomy

Abstract: Ultra-High-Energy (UHE, E $&gt;100$ TeV) gamma rays are one of the few channels to search for and study Galactic PeVatrons. Among the most promising PeVatron candidates are the many UHE gamma-ray sources that have recently been identified on the Galactic Plane. Ground-based particle detectors see these sources as extended rather than point-like, and current generation Imaging Atmospheric Cherenkov Telescopes (IACTs) struggle to study them with effective areas and background rejection that are suboptimal at UHE. A cost-efficient way of constructing an array of IACTs explicitly designed for UHE sensitivity is to sparsely separate many small telescopes. We have simulated, prototyped, and twice deployed a pathfinder array that is instrumented with telescopes designed by the Panoramic Search for Extraterrestrial Intelligence (PANOSETI) team. These 0.5-meter Fresnel lens telescopes are purpose-built for imaging optical transients on nanosecond timescales and are equipped with a $10<sup>\circ\times10<sup>\circ$ silicon photomultiplier camera. Three PANOSETI telescopes were deployed twice in the same temporary configuration at Lick Observatory in March and October 2024. Here we give a brief description of the instrument and present a comparison of simulations with the data collected, including an analysis of the Crab Nebula. We also report on the ongoing deployment of PANOSETI telescopes for the Dark100 array that is planned to operate for five years at Palomar Observatory.