A. D. Krasilnikov

The spectrum features of UHECRs below and surrounding GZK

The energy spectrum of ultra-high energy cosmic rays (UHECRs) is discussed on the basis of the Yakutsk array database analysis. In the region E 0 = 10 17 to 3 × 10 19 eV the showers are detected under trigger-500, while at energies above 3 × 10 19 eV the whole acceptance area for trigger-1000 is used in order to utilize all the data available in the region of Greisen-Zatsepin-Kuzmin (GZK) cutoff. Updated relations are adapted to estimate the primary energy having detected densities of charged particles at the distance 300/600 m from the shower axis.

Wide field-of-view Cherenkov telescope for the detection of cosmic rays in coincidence with the Yakutsk extensive air shower array

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.

SPECTRUM OF COSMIC RAYS WITH ENERGY ABOVE 1017 EV

The energy spectrum of primary cosmic rays with ultra-high energies based on the Yakutsk EAS Array data is presented. For the largest events values of S600 and axis coordinates have been obtained using revised lateral distribution function. The effect of the arrival time distribution at several axis distance on estimated density for Yakutsk and AGASA is considered.

The engineering prototype of the wide-field Cherenkov telescope for the Yakutsk array

The Yakutsk array group is developing the wide FOV Cherenkov telescopes to be operated in coincidence with the surface detectors of the array under modernization. Currently the engineering prototype of the reflecting telescope with front-end electronics is designed and assembled to prove the feasibility of the concept. In this report the status and parameters of the engineering prototype are presented.

A search for extragalactic sources of cosmic rays in the ultra-high energy domain

The arrival directions of ultra-high energy cosmic rays detected with the Yakutsk extensive air shower array are analyzed in comparison with the available data from other giant arrays. A correlation with the coordinates of active galaxy nuclei as hypothesized sources of ultra-high energy cosmic rays is sought for.

Cosmic ray energy spectrum (>1017 eV) of the Yakutsk EAS array

The energy spectrum obtained on the Yakutsk array for the parameter S600 is compared with the results obtained on the AGASA and HiRes arrays and the latest Pierre Auger Observatory data. The discrepancy in the intensity of the energy spectra obtained in different experiments can be explained by the presence of systematic errors in shower energy estimations.