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.
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Acknowledgments
We would like to thank the Tibet ASγ collaborators for fruitful discussions. We would like to thank the anonymous referee for his valuable suggestions. This work was supported by JSPS KAKENHI Grants and the Inter-University Research Program of the Institute for Cosmic Ray Research.
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Kawata, K., Sako, T.K., Ohnishi, M. et al. Energy determination of gamma-ray induced air showers observed by an extensive air shower array. Exp Astron 44, 1–9 (2017). https://doi.org/10.1007/s10686-017-9530-9
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DOI: https://doi.org/10.1007/s10686-017-9530-9