The energy spectrum of UHECRs is discussed on the basis of the Yakutsk array database analysis. In the region E=0.1 to 30 EeV the showers are detected under trigger-500, while at energies above 30 EeV the whole acceptance area for trigger-1000 is used in order to utilize all the data available in the region of GZK cutoff.Comment: Invited talk at CRIS2004: GZK and surroundings, Catania, Italy, 31.05.04. To appear in Nucl. Phys. B Proc. Supp

The Earth's magnetic field effect on the azimuthal distribution of extensive air showers (EAS) of cosmic rays has been evaluated using a bulk of the Yakutsk array data. The uniform azimuthal distribution of the EAS event rate is rejected at the significance level 10 -14 . Amplitude of the first harmonics of observed distribution depends on zenith angle as A 1 ≈ 0.2×sin 2 θ and is almost independent of the primary energy; the phase coincides with the magnetic meridian. Basing upon the value of measured effect, the correction factor has been derived for the particle density depending on a geomagnetic parameter of a shower. . In [4 a, b] it was shown that the showers initiated by extremely high energy photons have to show the north-south asymmetry. But the last effect has a threshold for the primary energy: E γ > 3⋅10 19 eV. In this paper we draw attention to the fact that due to the LDF asymmetry depending on χ, one can select the showers of equal energy and zenith angle in order to obtain the azimuthal modulation of the EAS event rate because of the different LDF stretch which causes the different observed primary cosmic ray energy and intensity.

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.

No abstract

No abstract