Field tests of a new high-speed pattern recognition trigger for ground-based gamma-ray telescope arrays

Abstract

We have developed a three-stage, high-speed trigger for use in an array of imaging atmospheric Cherenkov telescopes (IACTs), which are used for the study of cosmic high-energy gamma-ray sources. This trigger has the ability to recognize patterns of Cherenkov light generated by gamma-ray initiated air showers in the atmosphere and correlate these patterns across multiple telescopes in the IACT array to form a stereoscopic realtime pattern recognition trigger. New hardware and firmware sampling at 400MHz with programmable coincidence recognition timing and programmable delay compensation over 500 pixel channels in an IACT camera has been produced which generates triggers from the coincidence of any three adjacent pixels within the camera. Reduction of the required coincidence time to 5 ns and the concomitant reduction in dead time from the faster logic allow operation at lower discriminator thresholds relative to existing systems, enabling studies of lower energy gamma-ray events. A successful field test of the first two stages of this pattern recognition hardware has been performed on one of the IACTs of the VERITAS array located in Southern Arizona. We present the results of these tests and compare them to the performance of the existing VERITAS trigger system. A subsequent field test where hardware is connected to multiple VERITAS telescopes to exercise the stereoscopic features is in the planning stages.