Estimation of expected performance for the MACE [formula omitted]-ray telescope in low zenith angle range

Abstract

MACE (Major Atmospheric Cherenkov Experiment) is a Very High Energy (VHE) γ ray telescope, under installation at Hanle (32∘46′46′′ N, 78°58′35′′ E) in the Himalayan ranges of North India. It is a 21 m diameter dish and 25 m focal length Imaging Atmospheric Cherenkov Telescope (IACT) located at an altitude of 4270 m, highest for any existing IACT. In this paper, we estimate 4 performance characteristics of the MACE telescope, namely the trigger rate, the integral flux sensitivity, the angular resolution and the energy resolution in the dynamic energy range of ∼ 30 GeV–10 TeV in the low zenith angle range (< 30°). We observe that the integral rate of the MACE telescope for the 4 closed clusters nearest neighbor (CCNN) trigger with single-channel photoelectron threshold of 9.0 photoelectrons is 1.03 kHz. The integral flux sensitivity of the telescope is expected to be 2.4 % with the threshold energy of 31 GeV. We employ the Random Forest method (RFM) and show that the MACE telescope is estimated to have an angular resolution, defined as the σ of a 2-dimensional Gaussian distribution, of ∼0.21° in the energy range of 30.0–47.0 GeV. The angular resolution improves with increasing γ-ray energy and reaches to a value of ∼0.06° in the energy range of 1.8 TeV–3 TeV. We also evaluate 68% containment radius (σ0.68) for the distribution of reconstructed arrival directions as an alternative estimate of angular resolution. We find σ0.68 to steadily improve from a value of 0.36°in the energy range of 30.0–47 GeV to a value of ∼0.09° in the energy range of 1.8–3 TeV. We also reconstructed γ-ray energies using the regressive RFM and estimated the energy resolution, defined as the σ of the 1-D Gaussian fitted to distribution of fractional difference between the true and estimated energy, as a function of γ-ray energy. The MACE telescope is estimated to have energy resolution of ∼40% in the energy range (30–47) GeV (close to the analysis energy threshold of the MACE telescope), which improves to ∼19.8% in the energy bin of 1.8–3 TeV. The bias in the corresponding energy ranges improves from ∼36% to ∼−0.2%.