UC San Diego

We report on the initial on-sky results from the Panoramic Search for Extraterrestrial Intelligence (PANOSETI) experiment deployed at Palomar Observatory. PANOSETI is a wide-field optical observatory designed to explore fast optical phenomena across nanosecond-to-second timescales. Building on system verification at Lick Observatory, the Palomar deployment comprises four telescope sites, enabling cross-site coincidence detection and contributing to a broader science program encompassing optical technosignature searches, ultra-high-energy phenomena, and time-domain astrophysics. We summarize the performance of the deployed 0.48-meter f/1.32 Fresnel lens telescopes, which operate in two complementary readout modes: pulse height mode for nanosecond-scale triggered events and continuous imaging mode for variability on millisecond-to-second timescales. The detector characterization presented here focuses on the pulse-height readout mode. We characterize the Hamamatsu silicon photomultiplier (SiPM) detector focal plane through triggering rate curves, sky background as a function of lunar conditions, and false-alarm statistics across single- and multi-telescope coincidence configurations. We derive the two-telescope coincidence rate from measured triggering rate curves and establish the detection thresholds and operational baseline for the survey program. We present on-sky results for one of the technosignature observational fields, showcasing PANOSETI capabilities in this field.