Data Analysis

The experiment was operating stably during the data taking period from 2014 February to 2017 May. This work extends the observed zenith-angle range up to \(50^{\circ }\) from the conventional range up to \(40^{\circ }\) in previous studies. The extension improves the photon statistics by \(30\%\) for the sources studied in this work. From a Monte Carlo analysis, the angular and energy resolutions of the experiment for sub-PeV gamma rays are estimated to be \({\simeq } 0.2^{\circ }\) and \({\simeq } 30\%\) , respectively. The event selection using the data recorded with the MD array can highly improve the sensitivity of the experiment to sub-PeV gamma rays; it rejects more than \(99.9\%\) of the CR background in the sub-PeV energy range, while it gives the survival ratio of \(\gtrsim 70\%\) of sub-PeV gamma rays. The systematic uncertainty in the energy estimation with the AS array is estimated to be \(12\%\) from the observation of the Moon’s shadow made by CRs. On the other hand, the systematic uncertainty in pointing is estimated through the observation of the Crab Nebula; for TASG J1844−038, it is \(0.098^{\circ }\) and \(0.089^{\circ }\) along the right ascension and the declination, respectively, and for HESS J1849−000, \(0.058^{\circ }\) and \(0.055^{\circ }\) .