Third Level Trigger for the Fluorescence Telescopes of the Pierre Auger   Observatory
  The trigger system for the Auger fluorescence telescopes is implemented in hard- and software for an efficient selection of fluorescence light tracks induced by high-energy extensive air showers. The algorithm of the third stage uses the multiplicity signal of the hardware for fast rejection of lightning events with above 99% efficiency. In a second step direct muon hits in the camera and random triggers are rejected by analyzing the space-time correlation of the pixels. The trigger algorithm was tested with measured and simulated showers and implemented in the electronics of the fluorescence telescopes. A comparison to a prototype trigger without multiplicity shows the superiority of this approach, e.g. the false rejection rate is a factor 10 lower. 
A. Schmidt (1), T. Asch (1), H. Gemmeke (1), M. Kleifges (1), H.-J.   Mathes (2), A. Menshikov (1), F. Sch\"ussler (2), D. T...