On the calibration of ultra-high energy EASs at the Yakutsk array and Telescope Array

An analysis of calibrations of extensive air showers with zenith angles $\theta \le {50}^{\circ }$ and energies $E_{\text{SD}}\ge {10}^{18.5}$ eV was carried out in experiments at the Yakutsk array and Telescope Array. The values of $E_{\text{SD}}$ were determined from particle densities measured with ground-based scintillation detectors at a distance $r=800$ m from shower axis. Measured densities were compared with the values obtained in simulations preformed with the use of CORSIKA code within the framework of QGSJet-II.04 hadron interaction model for primary protons. For showers with $\theta =0^{\circ }$ the $E_{\text{SD}}$ estimates of both arrays are very close, and their energy spectra are similar in shape and absolute value. Another Telescope Array calibration, based on measuring the EAS fluorescent radiation with optical detectors, gives underestimated energy $E_{\text{FD}}=0.787\times E_{\text{SD}}$.