Terrestrial Gamma-Ray Flashes at the Pierre Auger Observatory

The Pierre Auger Observatory is designed to measure the highest energy cosmic rays. However, the surface detector, covering 3000 km$^2$, 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.