Simulation studies of MACE-I: Trigger rates and energy thresholds

The MACE (Major Atmospheric Cherenkov Experiment) is an upcoming Very High Energy (VHE) γ-ray telescope, based on imaging atmospheric Cherenkov technique, being installed at Hanle, a high altitude astronomical site in Ladakh, India. Here we present Monte Carlo simulation studies of trigger rates and threshold energies of MACE in the zenith angle range of 0°-60° for on-axis γ-ray coming from point source and various cosmic ray species. We have simulated the telescope's response to γ-rays, proton, electron and alpha initiated atmospheric Extensive Air Showers (EAS) in the broad energy range of 5 GeV to 20 TeV. For γ-rays we consider power law and log parabolic spectra while other particles are simulated with their respective cosmic ray spectrum. Trigger rates and threshold energies are estimated for the trigger configuration of 4 Close Cluster Nearest Neighbour(CCNN) pixels as implemented in MACE hardware, in combination with single channel discriminator threshold ranging from 6-10 photo electrons (pe). We find that MACE can achieve the γ-ray trigger energy threshold of ∼ 17 GeV (4 CCNN, 9 pe) at 0° zenith angle for power law spectrum. The total trigger rate at 0° zenith is expected to be ∼650 Hz, with protons contributing ∼ 80% to it. For the zenith range of 0°-40° we find that the telescope can achieve γ-ray trigger threshold energies of ∼22 GeV at 20° zenith angle and ∼40 GeV at 40° zenith angle. Integral rates are also almost constant for this zenith angle range. At zenith angle of 60°, trigger energy threshold increases to ∼173 GeV and total integral rate falls down to ∼305 Hz.