N. N. Kalmykov

Estimate of the fraction of primary photons in the cosmic-ray flux at energies ∼1017 eV from the EAS-MSU experiment data

We reanalyze archival EAS-MSU data in order to search for events with an anomalously low content of muons with energies Eμ > 10 GeV in extensive air showers with the number of particles Ne ≳ 2 × 107. We confirm the first evidence for a nonzero flux of primary cosmic gamma rays at energies E ∼ 1017 eV. The estimated fraction of primary gamma rays in the flux of cosmic particles with energies E ≳ 5.4 × 1016 eV is εγ = (0.43−0.11+0.12)%, which corresponds to the intensity Iγ = (1.2−0.3+0.4) × 10−16 cm−2 s−1 sr−1. The study of arrival directions does not favor any particular mechanism of the origin of the photon-like events.

Energy spectrum and mass composition of cosmic rays, by the data of the Tunka-133 array

The Tunka-133 Cherenkov light array for the detection of extensive air showers (EAS) acquires data over the five winters from 2009 to 2014. The direction of arrival, the shower core coordinates on the plane of observation, the primary energy, and the depth of the shower maximum are reconstructed for each EAS. A differential all-particle energy spectrum is obtained in the energy range of 6 × 1015–3 × 1018 eV over 1540 h, along with the energy dependence of the average depth of the shower maximum in the range of 6 × 1016–3 × 1018 eV. Based on this dependence, the variation in the average composition of the primary cosmic rays is estimated as a function of energy.

First results from the operation of the prototype Tunka-HiSCORE array

The Tunka-HISCORE wide-angle Cherenkov array, one part of the planned TAIGA integrated gamma observatory intended for investigations in the field of high-energy (>30 TeV) gamma-ray astronomy and cosmic-ray physics, is deployed in the Tunka Valley (Buryat Republic). The first results from operating a prototype array composed of nine stations spread over an area of ∼0.1 square kilometers during the winter of 2013–2014 are presented. Data processing techniques are described, along with data on the accuracy of reconstructing the position of a shower’s axis, energy, and angle of arrival. The differential spectrum of all cosmic-ray particles in a shower in the energy range of 2 × 1014 to 2 × 1016 eV is presented and compared to the available data.

Primary cosmic ray composition at energies from 1017 to 1018 eV according to the EAS MSU array data

EAS MSU array data on the composition of primary cosmic rays at energies above 1017 eV are analyzed. The problem of existence of a cosmic ray component that is not related to the conventional mechanism of formation of galactic cosmic rays is considered and the fraction of γ rays in primary cosmic rays is estimated.

Mass composition of 1017- to 1018-eV primary cosmic rays according to data on the lateral distribution of radio emission from extensive air showers

Experimental data obtained for the lateral distribution of radio emission from extensive air showers (EAS) at the array of Moscow State University (30–34 MHz) and the LOPES array (40–80 MHz) were comparedwith the results of calculations performed within amicroscopic approach based on aMonte Carlo simulation of EAS (CORSIKA code). The same experimental data were used to reconstruct the distribution of the depth of the EAS maximum at cosmic-ray energies in the range of 1017–1018 eV. The energy dependence of the depth of the EAS maximum was constructed for the case of data from the LOPES array, and the mass composition of cosmic rays was estimated for this case. From the resulting dependences, it follows that the mass composition shows a trend toward becoming lighter in the energy range being considered

Spectrum and composition of cosmic rays at energies of 1015–1018 eV

The energy spectrum and mass composition of primary cosmic rays at energies of 1015–1018eV are considered on the basis of experimental data from the EAS MSU array, which detects showers by charged particles, and the Tunka-25 array, which uses shower-produced Cherenkov radiation to detect EASs. A change in composition due to an increase in the fraction of heavy nuclei is shown to occur starting from the energy of the knee in the primary energy spectrum and up to 1017 eV. At energies above 1017 eV, an additional component that is unrelated to the bulk of the Galactic cosmic rays generated by shock waves in supernova explosions may appear in the energy spectrum. In this case, the fraction of heavy nuclei begins to decrease and the composition is again enriched by light nuclei. A brief description of the new Tunka-133 array with an area of about 1 km2 is given

Energy spectrum and mass composition of primary cosmic rays at energies 1015–1018 eV

Data on muon and electron components of extensive air showers (EAS) (obtained with the EAS MSU array) were used to derive the primary cosmic ray (PCR) mass composition. It is shown that for energies beyond the knee at energy 3 × 1015 eV the abundance of heavy nuclei increases with energy. But at energies above 1017 eV the abundance of light nuclei starts to grow. The primary cosmic ray spectrum in the range 1015–1018 eV is analyzed. It is shown that at energies above 1017 eV the additional component appears and it differs from the bulk of Galactic cosmic rays generated by shocks in SN remnants.

Constraints on the flux of

Results of the search for

\sim (10^{16} - 10^{17.5})

sim (10^{16} - 10^{17.5})

eV cosmic photons from the EAS-MSU muon data

eV primary cosmic-ray photons with the data of the Moscow State University (MSU) Extensive Air Shower (EAS) array are reported. The full-scale reanalysis of the data with modern simulations of the installation does not confirm previous indications of the excess of gamma-ray candidate events. Upper limits on the corresponding gamma-ray flux are presented. The limits are the most stringent published ones at energies