$X_{max}$ reconstruction for EAS with energy above $10^{16}$ eV from responses of tracking Cherenkov detectors

This work describes the system of tracking detectors operating at the Yakutsk complex EAS array. A technique is given for calculation of number of photons arriving from different heights of the atmosphere from the detector response and, thus, to reconstruct the longitudinal development of individual showers. We present the results of direct observations of the cascade curve and give the depth of maximum shower development determined from the measurement of the Cherenkov emission from EAS. From the comparison between experimental values of Xmax with simulation results based on the QGSJET-II-03 model for different primary particles, a preliminary conclusion was made on the cosmic rays mass composition in the energy range 10^{16}-10^{18} eV.