Energy determination of gamma-ray induced air showers observed by an extensive air shower array

Abstract

We propose a new energy estimator to determine the energies of gamma-ray induced air showers based on the lateral distribution of extensive air showers in the energy range between 10 TeV and 1000 TeV. We carry out a detailed Monte Carlo simulation assuming the Tibet air shower array located at an altitude of 4,300 m above sea level. We define S50, which denotes the particle density at 50 m from the air shower axis, as a new energy estimator. Using S50, the energy resolution is estimated to be approximately 16 % at 100 TeV in the range of the zenith angle 𝜃 < 20∘. We find S50 giving a better energy resolution than 27 % for the air shower size (N e) and 30 % for the sum of detected particles ( $\sum \rho $ ), which have been used so far, at 100 TeV. We also compare the reconstructed age distributions of gamma-ray induced air showers and hadronic cosmic-ray induced air showers. The age parameter may help to discriminate between primary gamma rays and hadronic cosmic rays.