Trigger system of the MAGIC telescope

The MAGIC telescope aims at the detection of very low energy gamma rays (E > 10 GeV) through the atmospheric emission of Cherenkov light. The high background rate originated by the night sky background (NSB), unions, hadronic showers and bright stars sets a seriuos challenge to this goal. Application of topological selection cuts at trigger level can have a big impact on the background reduction allowing the telescope to operate at lower thresholds and reducing the minimum detectable energy. The trigger of the MAGIC telescope is a two-level system following a pipeline philosophy, similar to those adopted in the high energy experiments. Operative since october 2002, the trigger system has been a key point in the commissioning of the MAGIC telescope that is now taking data. The trigger hardware is described in detail.