Three regions of an excessive flux of PeV cosmic rays

Three regions of an excessive flux of cosmic rays with energies of the order of PeV are found in the experimental data of the EAS MSU array at a confidence level greater than 4σ. For two of them, there are similar regions in the experimental data of the EAS-1000 Prototype array. One of the interesting features of the regions is the absence in their vicinities of supernova remnants, traditionally considered as the main sources of Galactic cosmic rays, and the presence of pulsars, some of which are able to accelerate heavy nuclei up to energies close to PeV. In our opinion, this favors the conjecture that isolated pulsars are able to contribute to the flux of Galactic cosmic rays more than it is usually assumed.     

On the estimate of the energy of the nuclei of primary cosmic radiation generating extensive air showers

The analysis of the systematic errors in the determination of the energy of the particles of primary cosmic radiation that are inherent in the method for measuring extensive air showers (EASs) indicates the necessity of the exact inclusion of fragmentation in the nuclear interactions. The application of such a model developed for describing the experiments at the Relativistic Heavy Ion Collider improves the agreement between the energy spectra of the ultrahigh-energy cosmic rays measured at giant EAS arrays. It has been shown that the difference between the measured primary cosmic radiation flux intensities and the energies of the primary particles is within the methodical and instrumental errors. The real accuracy of the EAS method of studying ultrahigh-energy cosmic rays has been estimated using the data from six arrays.     

On the composition of cosmic rays with E 0 ≥ 1017 eV according to the Yakutsk EAS array data

The energy spectrum and anisotropy of primary cosmic rays, as well as the lateral distribution functions of electrons and muons in extensive air showers (EASs) with E ₀ ≥ 10¹⁷ eV, are presented according to the Yakutsk EAS array data. It has been shown that the spectrum and lateral distribution functions in some energy ranges have different shapes for the particles that arrive from the disc of the Supergalaxy (Local Supercluster of galaxies) and from the other part of the celestial sphere. This is interpreted as the manifestation of the interaction of extragalactic primary cosmic rays with the gas of the Supergalaxy that possibly leads to the production of new ultra-high-energy particles.     

Search for sources of cosmic rays in the region of the knee: Part II

This paper reports on new results obtained from analyzing the arrival directions of extensive air showers detected at the Prototip ShAL-1000 array in the period from the end of August 1997 to February 2001. The results are examined using the method proposed by Alexandreas and colleagues, which has been widely employed for analyzing the data obtained from other experiments. The existence of the previously revealed zones with an excessive flux of cosmic rays at energies in the range of the knee and the closeness of the coordinates of these zones to those of the possible astrophysical cosmic-ray sources are confirmed.     

Testing calculation results of Cherenkov radiation flux from extensive air showers using CORSIKA

This paper presents computational results of the spatiotemporal characteristics of Cherenkov light from particles of extensive air showers (EASs) induced by ultra-high-energy cosmic rays (UHECR). These results were obtained by simulating EAS events with the CORSIKA software package. Events were induced by UHECR particles, i.e., protons and iron nuclei with energies of 10¹⁵ and 10¹⁶ eV. The computational results were compared with experimental data obtained at the Yakutsk EAS array; possible causes of the discrepancy between them are discussed.     

Searching for preferential arrival directions of ultrahigh-energy cosmic rays on the Moscow State University EAS array

There is evidence for possible clustering in the arrival directions of extensive air showers (EASs). A program for analyzing EAS arrival directions has been developed to investigate this problem and the database of the Moscow State University EAS array for 1982–1989 has been analyzed. The distributions in equatorial coordinates have been derived for cosmic rays with energies E ≥ 2 × 10¹⁵ eV and zenith angles <40°. The uniformity of the derived distributions is verified using various statistical tests.     

The Carpet-3 experiment to search for diffuse gamma rays with energies of more than 100 TeV

An experiment for measuring the flux of cosmic diffuse gamma rays with energies above 100 TeV (the Carpet-3 air shower array) is now being prepared at the Baksan Neutrino Observatory, Institute for Nuclear Research, Russian Academy of Sciences. The preparations entail a substantial increase of the areas of both the muon detector and the surface air shower array. The experiment’s sensitivity to showers generated by primary gamma rays is estimated for different configurations of the array. In addition, preliminary estimates of the upper limit on the flux of diffuse gamma rays with energies higher than 1.3 PeV, derived using experimental data from the old Carpet-2 array, are presented for a net exposure time of 9.2 years.     

TUNKA-133: A new array for the study of ultra-high energy cosmic rays

A new array for studying ultra-high energy cosmic rays was inaugurated in 2009 in the Tunka Valley, about 50 km from Lake Baikal. Having an area of 1 km², the new facility allows us to study cosmic rays with energies of 10¹⁵–10¹⁸ eV via the a unified method for registering Cherenkov radiation from extensive air showers (EASes) and is making a substantial contribution to understanding the origin of ultra-high energy cosmic rays. We describe the current state of the experiment, the new methodological approach, our initial results, and the plans for further development of the array.     

Primary cosmic ray composition at energies from 10<Superscript>17</Superscript> to 10<Superscript>18</Superscript> 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.     

Modernization of the Carpet-2 array of the Baksan Neutrino Observatory

The state of the art and the project of modernization of the extensive-air-shower array Carpet-2 of the Baksan Neutrino Observatory of the Institute for Nuclear Research, Russian Academy of Sciences are described. The modernized array will allow the performance of detailed study of variations in the cosmic ray intensity, the energy spectra and composition of primary cosmic rays in the energy range 10¹³–10¹⁶ eV, and the anisotropy of primary cosmic rays with energies above 10¹³ eV.     

Anisotropy of arrival directions of E 0 ⩾ 8 × 1018 eV cosmic rays and cosmic microwave background

Results are presented that were obtained by analyzing the arrival directions of E ₀ ? 8 × 10¹⁸ eV primary cosmic rays recorded at the Yakutsk array over the period between 1974 and 2003 and at the SUGAR array (Australia). The greatest primary-cosmic-ray flux is shown to arrive from the region of visible intersection of the planes of the Galaxy and the Supergalaxy (local supercluster of galaxies) at a galactic longitude of about 137°. On a global scale, the lowest temperature of the cosmic microwave background is typical of this region.     

Search for anisotropy in arrival directions of ultrahigh-energy cosmic rays by using the marr wavelet on the equatorial sphere

The arrival direction distribution of cosmic rays for energies E>10¹⁸ eV detected at the Yakutsk EAS array is analyzed using the Marr wavelet. Deviation from the isotropic distribution of 361 showers above 10¹⁹ eV is found at a significance level of 0.007, which corroborates previous evidence of the cosmic ray anisotropy in this energy range. In contrast to the previous methods, the wavelet analysis makes it possible to localize both a celestial-sphere domain containing a supposed source of excess cosmic ray flux and the scale parameter of the two-dimensional wavelet.     

Arrival directions and chemical composition of ultrahigh-energy cosmic rays

Chemical composition of ultrahigh-energy cosmic rays is estimated through the reliably determined (both experimentally and theoretically) distribution of the number of showers in the galactic latitude. Experimental data at energies of ～10¹⁹ eV agree with the theoretical calculations, provided that cosmic rays involve predominantly heavy nuclei. An enhanced flux of cosmic rays from the galactic plane is detected at energies of ～10¹⁹ eV.     

Analysis of the anisotropy of the muon flux, according to data obtained by the URAGAN muon hodoscope during heliospheric disturbances

Features of studying heliospheric disturbances caused by changes in the parameters of the interplanetary magnetic field by the anisotropy of the muon flux of cosmic rays detected on the surface of the Earth by the URAGAN muon hodoscope are considered. The anisotropy of the muon flux in the period 2007–2011 is analyzed. The forecasting potential of our approaches to studying heliospheric disturbances using the penetrating component of cosmic rays is evaluated.     

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.     

Ultra-High Energy Cosmic Ray Study Results by Radio Emission Technique at Yakutsk Array

Physics of Atomic Nuclei - The Yakutsk array is designed to study cosmic rays at energy 1015–1020 eV. The array detects charged particles, muons, Cherenkov light and radio emission....     

Features of cosmic ray variation at the phase of the minimum between the 23rd and 24th solar cycles

The minimum between the 23rd and 24th cycles of solar activity was unusually deep and extended. The modulation of cosmic rays was minimal for the more than 70-year-long period of direct measurements. The data from stratospheric measurements by the Lebedev Physical Institute suggest that the flux of cosmic rays with more than 100 MeV/nucleon of energy exceeded the highest ever observed level (May 1965) by almost 12%. However, the ground-based neutron monitors sensitive to relatively high energies indicated that the flux of cosmic rays increased by less than 3%. This work compares the variations in the cosmic rays over periods of five minima of solar activity (the 20th to the 24th cycle). It is shown that in late 2008, an extra flux of particles with energies less than several GeV/nucleon was detected in the Earth’s orbit. A similar (though far smaller in scale) phenomenon was also observed in 1987 at the same orientation of the Sun’s magnetic field A < 0, but was not observed in epochs where A > 0.     

Connections between neutron monitor count rate and solar modulation strength

We suggest a new approach to the normalisation of neutron monitor response to galactic cosmic rays. The reference normalisation count rate is the neutron monitor response to the model unmodulated flux of galactic cosmic rays. A comparison of the actually recorded neutron monitor count rate with the calculated normalisation count rate can provide one with an observationally obtained true-of-date integral measure of the current level of solar modulation of galactic cosmic rays. The Slovak VEGA grant agency is acknowledged for the grant 2-5137.     

Variable composition of cosmic rays with E 0 ≥ 1017 eV according to the data from the muon detectors of the Yakutsk EAS array

The lateral distribution of muons with the threshold E _μ ≈ 1.0 secθ GeV (where θ is the zenith angle) in extensive air showers (EASs) with the energy E ₀ ≈ 10^17–19 eV in various observation periods from November 1987 to June 2013 has been analyzed. The experimental data have been compared to the calculations within various models of the development of EASs from the CORSIKA package. The experimental data are in the best agreement with the QGSJET II-04 model. The mass composition of cosmic rays with E ₀ < 2 × 10¹⁸ eV before 1996 was much lighter than that in a later time interval.