I. T. Makarov

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.

Muon component of EAS with energies above 1017 eV

Abstract Experimental data on muons (with threshold energy of 1 GeV) in extensive air showers (EAS) obtained at the Yakutsk EAS array from 1974 to 1992 are presented. Periods of reliable detector operation have been selected. Muon detector readings near the threshold have been carefully taken into account. Mean lateral distribution functions (LDF) of muons in the energy range of 1017–5 × 1019 eV and the zenith angle range of 0–60 ° have been obtained. The dependence of LDF on E0 and θ at energies above 5 × 1018 eV is shown to be considerably different in comparison with the region of lower energies.

MUONS WITH Eth ≥ 1 GEV AND MASS COMPOSITION IN THE ENERGY RANGE 1018 - 1020EV OBSERVED BY YAKUTSK EAS ARRAY

The ratio of the muon flux density to charged particle flux density at distances of 300 and 600 m from the shower axis (ρμ(300)/ρs(300) and ρμ(600)/ρs(600)) is measured. In addition, the energy dependence of ρμ(1000) is analysed for showers with energies above 1018 eV. A comparison between the experimental data and calculations performed with the QGSJET model is given for the cases of primary proton, iron nucleus and gamma-ray. We conclude that the showers with E0 ≥ 3 × 1018eV can be formed by light nuclei with a pronounced fraction of protons and helium nuclei. It is not excluded however that a small part of showers with energies above 1019 eV could be initiated by primary gamma-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.

Energy spectrum of ultra-high energy cosmic rays according to surface detectors of Yakutsk EAS array

We present the results of the analysis of cosmic rays spectrum in energy domain above

Characteristic features of EAS in the energy range of 50–500 PeV by the Yakutsk data

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Characteristics of EAS and primary particle mass composition in the energy region of 1017–3⋅1019 eV by Yakutsk data

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.

Energy Spectrum of Primary Cosmic Rays in the Energy Region of 1017 1020 eV by Yakutsk Array Data

Data for the electron-photon, the muon and Cerenkov components of EAS, registered with the Yakutsk array during long data collection periods, are presented. The data appear of specific interest as control samples for the development of advanced hadronic interaction models and for checks of differences of various types of models (scaling procedures — QCD inspired models). Preliminary results of the analysis exhibit a satisfactory description of the experimental observations above 10 18 eV by scaling violation, and they require slightly larger multiplicities of the secondary particle production in the energy range of 50 – 500 PeV. The results appear also to be in agreement with a mixed composition in this energy range, approximately like that known for primaries of 10 12 eV. This conclusion is also consistant with the frequency of muons (≥ 1 GeV), observed at 300 m distance from the core of 50 – 500 PeV EAS.