Terrestrial Gamma-Ray Flashes at the Pierre Auger Observatory

Abstract The Pierre Auger Observatory is designed to measure the highest energy cosmic rays. However, the surface detector, covering 3000 km2, is also sensitive to events associated with atmospheric electricity. These events can be distinguished from normal cosmic-ray events in both temporal and spatial structure. With signals lasting around 10 μs, they are about an order of magnitude longer than cosmic-ray events. Their circular footprints on the ground are also different and larger than those of typical cosmic-ray showers. Due to their association with thunderstorms and topology, these events are candidates for downward-going terrestrial gamma-ray flashes (TGFs). We show a detailed analysis of the effects that the data-taking system has on recording of TGF candidate events. Furthermore, we present a recently implemented special trigger algorithm aimed at increasing the data-taking efficiency for TGF candidates.