The fluorescene detector electronics of the Pierre Auger Observatory

The Pierre Auger Observatory is a hybrid experiment to observe cosmic ray extensive air showers with energies above 1019 eV by a combination of a surface array and air fluorescence detectors (FD). Prototypes of both these detectors have been successfully tested and operated. Currently the final design version of the electronics is undergoing installation. Based on experience gained with the prototype we present the concept of the FD electronics and the implemented trigger algorithms. The electronics continuously record the image of the 20×22 pixel camera in a ring buffer of 100 μs length with a time resolution of 100 ns. Digital trigger algorithms analyse these data to find straight tracks originating from the fluorescence light. All individual detectors are synchronized with a 10 MHz signal generated by a GPS clock module. Veto and dead time signals are centrally distributed to allow calibration with external light sources during normal operation. A statistical method for the calibration was developed and tested.