Recent results from the Pierre Auger observatory on lightning related events

The Pierre Auger Observatory, the biggest hybrid detector in the world designed to observe cosmic rays at the highest energies, has turned out to be a valid instrument for studying transient phenomena related to atmospheric electricity. The fluorescence detector, which observed the first elves in 2005, operates as a 10 Mfps camera and represents an unprecedented opportunity to study the evolution of these phenomena with the best time resolution available. Since 2013, a dedicated trigger was added to allow detection and storage of elves events; the readout window was extended from 100μs to 300μs (2014-6), to 900μs (2017-8) in order to study more closely the light emission above the lightning source. Peculiar events related to lightning activity were also observed by the surface detector. They present a big footprint at the ground with a radius which goes from 2 to 8 km. The typical traces of these events are two orders of magnitude longer than cosmic-muon traces, and each event has at least one station with signal dominated by high-frequency noise. Studies are in progress to understand the origin of these anomalous events