A wide field-of-view Cherenkov telescope has been working in the surroundings of the Yakutsk array experiment since 2012. Its main function is to measure the waveform of the Cherenkov radiation signal induced by extensive air showers of cosmic rays. Analysis of the dataset collected by telescope is intended for the reconstruction of the parameters of the development of the shower in addition to the main shower characteristics measured by the rest of the array detectors. In this paper, the observed duration of the Cherenkov radiation signal as a function of the shower core distance is used to estimate the depth of the shower maximum in a different way, based on the results of model simulations.

The operation of a wide field-of-view Cherenkov telescope is described. The detection of extensive air showers (EAS) of cosmic rays (CR) is based upon the coincidence with signals from the Yakutsk array. The data acquisition system of the telescope yields signals connected with EAS development parameters: presumably, shower age and position of shower maximum in the atmosphere. Here we describe the application of digital signal processing in order to reconstruct Cherenkov radiation signals induced by CR showers.

The Yakutsk Extensive Air Shower Array has been continuously operating for more than 50 years (since 1970) and up until recently it has been one of world's largest ground-based instruments aimed at studying the properties of cosmic rays in the ultra-high energy domain. In this report we discuss results recently obtained at the array - on cosmic rays energy spectrum, mass composition and directional anisotropy - and how they fit into the world data. Special attention is paid to the measurements of muonic component of extensive air showers. Theoretical results of particle acceleration at shocks are also briefly reviewed. Future scientific and engineering plans on the array modernization are discussed.

The operation of a wide field-of-view (WFOV) Cherenkov telescope is described. Detection of extensive air showers (EAS) of cosmic rays (CR) is based on the coincidence with signals from the Yakutsk array. The data acquisition system (DAQ) of the telescope yields signals connected with EAS development parameters: shower age and position of shower maximum in the atmosphere. Here we describe the application of digital signal processing for reconstruction of Cherenkov radiation signals induced by air showers.

The operation of a wide field-of-view (WFOV) Cherenkov telescope is described. The detection of extensive air showers (EASs) of cosmic rays (CRs) is based upon the coincidence with signals from the Yakutsk array. The data acquisition system of the telescope yields signals connected with EAS development parameters: presumably, shower age and position of shower maximum in the atmosphere. Here, we describe the method of signal processing used to reconstruct Cherenkov radiation signals induced by CR showers. An analysis of signal parameters results in the confirmation of the known correlation of the duration of the Cherenkov radiation signal with the distance to the shower core. The measured core distance dependence is used to set an upper limit to the dimensions of the area along the EAS axis where the Cherenkov radiation intensity is above half-peak amplitude.

A fast-acting Cherenkov light detector with a high temporal resolution is described. The interest in such extensive air shower detectors is due to the need for more precise measurements of the Cherenkov pulse shape. The efficiency of the integral Cherenkov detector is demonstrated.

A proposed new method for measuring the Cherenkov light from extensive air showers (EAS) of cosmic rays (CR), which allows to determine not only the primary particle energy and angle of arrival, but also the parameters of the shower in the atmosphere - the maximum depth and “age”. For measurements, it is proposed to use Cherenkov light produced by EAS in a ground network of wide-angle telescopes, which are separated from each other by a distance 100-300 m depending on the total number of telescopes operating in coincidence, acting autonomously, or includes a detector of the charged components, radio waves, etc. as part of the EAS. The energy measurement and CR angle of arrival, data on the depth of the maximum and the associated mass of the primary particle generating the EAS is particularly important in the study of galactic cosmic rays for E> 10 14 eV, where currently there are no direct measurements of the maximum depth of the EAS.

This report presents a prototype Cherenkov telescope, the observation method of Cherenkov light from extensive air showers (EAS) generated by cosmic rays (CRs) above 1016 eV and preliminary observations. The interest in Cherenkov light differential detectors of EAS is caused by the possibility to measure the depth of the cascade maximum, Xmax, and/or the shower age via angular and temporal distributions of the Cherenkov signal. In particular, it was shown, using EAS model simulations, that the pulse width measured at the periphery of the shower, r > 300 m, at sea level is pronouncedly connected with Xmax. The Cherenkov detector is a wide-angle telescope working in coincidence with scintillation detectors, integral and differential Cherenkov detectors at the Yakutsk complex EAS.

We present the results of the analysis of cosmic rays spectrum in energy domain above $10^{17}$ eV. The analysis covers extensive air showers registered over the course of continuous observations from 1974 to 2017. A new refined relation was applied to reconstruct primary energy in individual events. It was derived from the lateral distribution of responses of surface and underground detectors of the Yakutsk EAS array obtained in air shower simulations with four hadron interaction models -- QGSJet01, QGSJet-II-04, SIBYLL-2.1 EPOS-LHC. The resulting new energy estimation is 1.4 times lower than the values obtained earlier with calorimetric method.

A proposed new method for measuring the cherenkov light from extensive air showers (EAS) of cosmic rays (CR), which allows to determine not only the primary particle energy and angle of arrival, but also the parameters of the shower in the atmosphere - the maximum depth and "age". For measurements it is proposed to use cherenkov light produced by EAS in a ground network of wide-angle telescopes which are separated from each other by a distance 100-300 m depending on the total number of telescopes operating in coincidence, acting autonomously, or includes a detector of the charged components, radio waves, etc. as part of the EAS. Results of such an array should be developed. The energy measurement and CR angle of the arrival data on the depth of the maximum and the associated mass of the primary particle generating by EAS. This is particularly important in the study of galactic cosmic ray for $E> 10^{14} $eV, where currently there are no direct measurements of the maximum depth of the EAS.

A proposed new method for measuring the cherenkov light from extensive air showers (EAS) of cosmic rays (CR), which allows to determine not only the primary particle energy and angle of arrival, but also the parameters of the shower in the atmosphere – the maximum depth and “age”. For measurements it is proposed to use Cherenkov light produced by EAS in a ground network of wide-angle telescopes which are separated from each other by a distance 100–300 m depending on the total number of telescopes operating in coincidence, acting autonomously, or includes a detector of the charged components, radio waves, etc. as part of the EAS. Results of such an array should be developed. The energy measurement and CR angle of the arrival data on the depth of the maximum and the associated mass of the primary particle generating by EAS. This is particularly important in the study of galactic cosmic ray for E > 1014 eV, where currently there are no direct measurements of the maximum depth of the EAS.

A way of observing the Cherenkov light from extensive air showers (EAS) generated by cosmic rays (CRs) with energies above 1016 eV is presented, along with preliminary results from observations. The detector is a wide-angle Cherenkov telescope working in coincidence with scintillation detectors and the integral and differential Cherenkov detectors of the Yakutsk EAS array. The detector is positioned about 2 m away from one of the integral Cherenkov detectors.

Cherenkov telescope for study cosmic rays L.V.TIMOFEEV Figure 1: The photo multiplier Hamamatsu R2486 with coordinate-sensitive anode consisting of 16X16 crossed wires has been chosen for the Cherenkov telescope prototype.

We analyze temporal characteristics of signals from the wide field-of-view (WFOV) Cherenkov telescope (CT) detecting extensive air showers (EAS) of cosmic rays (CRs) in coincidence with surface detectors of the Yakutsk array. Our aim is to reveal causal relationships between measured characteristics and physical properties of EAS.

The Yakutsk array group is developing a wide field-of-view Cherenkov telescope to be operated in coincidence with the surface detectors of the extensive air shower array. Currently, the engineering prototype of the reflecting telescope with the front-end electronics is designed, assembled, and tested to demonstrate the feasibility of the conceived instrument. The status and specifications of the prototype telescope are presented, as well as the modernization program of the already existing Cherenkov light detectors subset of the array measuring ultra-high energy cosmic rays.