Some very peculiar events have been recorded using the surface detector (SD) of the Pierre Auger Observatory. The signals produced by these events in the SD stations last about 100 times more
than those produced by cosmic rays. For many events, the number of stations having a long signal is big: for the largest events it goes up to 46 stations. The long-lasting stations are arranged in a
circular shape with a radius of about 6 km. Moreover, a correlation with lightning was observed. Many checks were performed to evaluate the possibility that electronics problems could generate the observed signals, but these checks revealed that the peculiar events are indeed produced by particles and/or photons that cross the Auger Cherenkov detectors. A search algorithm was implemented based on the duration of the signal. These events are very sporadic. Using a sample of ten “golden” events, studies are under way to characterize these events, and to understand their origin. The main features of these events will be described and a preliminary reconstruction will
be shown.