Trigger and Data Acquisition electronics for the Geiger-mode avalanche photodiode Cherenkov Telescope Camera of FACT

Within the framework of the FACT project (First G-APD Cherenkov Telescope), we develop and construct a camera based on Geiger-mode avalanche photodiodes (G-APD) for Imaging Atmospheric Cherenkov Telescopes. Such Cherenkov telescopes are the workhorses in ground-based very high energy gamma-ray astronomy. Compared to the currently used photomultiplier tubes, G-APDs promise higher photon detection efficiency, are more robust and operate at a much lower bias voltage. The FACT camera is equipped with 1440 pixels and data acquisition channels. Preamplifiers, data acquisition, trigger electronics and slow control are integrated in the camera. The readout system is based on the DRS4 analogue pipeline chip, operated at a default sampling rate of 2 GHz. Data transfer from the camera to the data acquisition computers is based on standard TCP/IP Ethernet connections. The trigger system uses analogue sums over trigger patches that consist of 9 pixels each, with the possibility to exclude individual pixels from the trigger generation.