On-line Selection Strategies for Cherenkov Telescopes

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), muons, hadronic showers and bright stars sets a serious callenge 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. We have developed a series of topological selection methods to be applied at the second level trigger. This technique has been applied to Monte Carlo data and has proven to be effective in rejecting up to 90% of the background events and doubling the collection area for shower energies below 100 GeV