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.     

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.     

Modeling Source Spectra and Composition of Ultrahigh Energy Cosmic Rays

The inverse problem of cosmic ray transport of ultra-high energy cosmic rays is considered. The source spectrum and composition are derived based on the recent Auger data on energy spectrum, energy dependence of mean logarithm of atomic mass number and its variance. The dependence of results on the extrapolation of observable spectrum beyond energies 10²⁰ eV is investigated.

     

Radio emission of extensive air showers as a method for detecting ultra-high energy cosmic rays

Recording radio emission from extensive air showers (EASs) is considered now as a new promising method for detecting ultra-high energy (E ₀ > 5 × 10¹⁶ eV) cosmic rays. The results of calculation of EAS radio emission at frequencies from 40 to 80 MHz in the EAS energy range E ₀ = 10¹⁴–10¹⁷ eV are reported here, and the possibilities of determining EAS parameters from the radio emission lateral distribution are discussed.     

Neutrino—nucleon cross-section at ultra-high energies in models with large extra dimensions

We examine whether the models with large extra dimensions can provide an explanation for the GZK violating ultra-high energy cosmic rays (UHECR). In these models the neutrino—nucleon cross-section rises rapidly with energy and hence cosmic rays might be identified with neutrinos. We calculate the neutrino-nucleon cross-section at ultra high energies by assuming that it is dominated by the production ofp-branes. We perform the calculation in a generalized Randall-Sundrum model and Lykken-Randall model and find cross-sections of the order of 100 mb at neutrino energies of 10²⁰ eV, which is required for explaining UHECR events.     

Tunka-133: Status 2008 and development of methods for data analysis

The activity on creation of a array with an area of 1 km² for recording extensive air showers using Cherenkov light began in the Tunka valley in 2006. The new array will allow one to study cosmic rays in the energy range 10¹⁵–10¹⁸ eV by the unified method. In the winter of 2007–2008, the array operated with 4 clusters, 7 detectors in each cluster. Experimental data obtained during 270 h of fair weather in moonless nights demonstrated unique capabilities of the new array, related with the possibility of recording the pulse shape with a step of 5 ns from each detector.     

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.     

The extensive air shower muon number spectrum beyond the knee in the cosmic-ray energy spectrum

The extensive air shower (EAS) muon number spectrum is obtained with increased statistics using the central muon detector of the EAS MSU array, which records muons with energies above 10 GeV. The dependence of the mass composition of primary cosmic rays on the energy is considered. The conclusion is confirmed that for energies from 3 × 10¹⁵ eV (the primary energy spectrum knee) up to 10¹⁷ eV a change in the composition associated with an increase in the proportion of heavy nuclei occurs; however, after the energy of 10¹⁷ eV, the proportion of heavy nuclei begins to decrease and the composition becomes lighter. A comparison with similar data from other experiments is conducted. The existence of an additional component of cosmic rays is confirmed; earlier an indication of its presence was derived from data on the EAS electron number spectrum.     

Determining the primary cosmic ray energy from the total flux of Cherenkov light measured at the Yakutsk EAS array

We present a method for determining the energy of the primary particle that generates an extensive air shower (EAS) of comic rays based on measuring the total flux of Cherenkov light from the shower. Applying this method to Cherenkov light measurements at the Yakutsk EAS array has allowed us to construct the cosmic ray energy spectrum in the range 10¹⁵ ? 3 × 10¹⁹ eV.     

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.     

Energy spectrum and mass composition of primary cosmic rays at energies 10<Superscript>15</Superscript>–10<Superscript>18</Superscript> 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 fraction of primary gamma rays at ultra-high energies from the muon data of the Yakutsk EAS array

By using data on the total signal and on the muon component of air showers detected at the Yakutsk array, the possible upper limits on the fraction of primary gamma rays at ultra-high energies is analyzed in the framework of the recently suggested event-by-event approach. Upper limits on the photon fraction in the integral flux of primary cosmic rays are derived. At 95% C.L., these limits are 22% for primary energies E ₀ > 4 × 10¹⁹ eV and 12% for E ₀ > 2 × 10¹⁹ eV. Despite the presence of muonless events, the data are consistent with the complete absence of photons at least at 95% C.L. The sensitivity of the results to systematic uncertainties, in particular to those of the energy determination for nonphoton primaries, is discussed. The text was submitted by the authors in English.     

Cosmic rays of extremely high energies and pulsars

Extensive air showers with energy above 4×10¹⁹ eV that were detected at the Yakutsk array from 1974 to 2001 are analyzed. The directions of their arrival are found to correlate with pulsars located in the direction of the Orion Arm of the Galaxy. The origin of cosmic rays is discussed.     

Cosmic rays of energies in the range 103–105 TeV and higher

Over a period of more than 30 years, the knee in the spectrum of extensive air showers (EAS) generated by cosmic radiation has been explained in two ways: as a consequence of a cusp in the energy spectrum of primary cosmic rays or as a consequence of a change undergone by the process of multiparticle hadron production in the interactions of primary protons with nuclei of air atoms. Investigations at the Tien Shan EAS array confirm a change in the properties of showers generated by protons near the upper boundary of the atmosphere and evince the invariability of the energy spectrum of protons in the energy range 10³–10⁵ TeV.     

Search for extragalactic sources of ultrahigh-energy cosmic rays

Possible extragalactic sources of cosmic rays with energies above 4 × 10¹⁹ eV detected at the Yakutsk EAS array are sought. The correlation of the shower arrival directions with objects from Véron’s catalog that are located closer than 100 Mpc from the Earth confirms the observations at the Pierre Auger Observatory, as well as the Greisen-Zatsepin-Kuzmin effect on the spectrum of cosmic rays. The detailed analysis of the data reveals the classes of objects belonging to the active galactic nuclei that are the most probable sources of ultrahigh-energy cosmic rays.     

On the origin of <Emphasis Type="Italic">E</Emphasis><Subscript>0</Subscript> ≥ 10<Superscript>17</Superscript> eV cosmic rays according to data from the Yakutsk array for studying extensive air showers

Results are presented that were obtained by analyzing the energy spectrum and anisotropy of E ₀ ≥ 10¹⁷ eV primary cosmic rays on the basis of data accumulated at the Yakutsk array for studying extensive air showers over the period between 1974 and 2004. It is shown that spectra corresponding to different regions of the sky differ in shape. Particle fluxes going from the Galaxy and Supergalaxy (a local supercluster of galaxies) disks are enhanced for E ₀ ≥ 5 × 10¹⁸ eV and are reduced for E ₀ ≤ (2–3) × 10¹⁸ eV. This observation is interpreted as a manifestation of the possible interaction between extragalactic primary cosmic rays and matter of the above structures of space.     

Investigation of the properties of the flux and interaction of ultrahigh-energy cosmic rays by the method of local-muon-density spectra

A new method for studying extensive air showers is considered. The method is based on the phenomenology of the localmuon density. It is shown that measurement ofmuon-density spectra at various zenith angles makes it possible to obtain information about the energy spectrum, mass composition, and interaction of cosmic rays over a broad range of energies (10¹⁵–10¹⁸ eV) by using a single array of comparatively small size. The results obtained from a comparison of experimental data on muon bundles from the DECOR coordinate detector with the results of simulation performed under various assumptions on the properties of the primary flux and for various hadron-interaction models are presented, and possible versions of the interpretation of these results are discussed.     

The surfatron acceleration of cosmic rays in the galactic plasma

The optimum conditions for a prolonged holding of charged particles resonantly trapped from the galactic plasma by nonlinear waves and for the acceleration of these particles to high energies by the surfatron mechanism are established. The density of particles trapped by the plasma waves of large amplitude and by the quasitransverse magnetosonic shock waves is estimated. Various reasons leading to possible breakage of the process of surfatron acceleration of cosmic rays in the Galaxy are considered. Within the framework of the surfatron acceleration mechanism, galactic cosmic rays originate predominantly from the interstellar plasma and their energy spectrum is formed in two stages. In the first stage, some of the galactic plasma particles are accelerated from thermal energies to 10¹⁵ eV/nucleon; in the second stage, the cosmic rays may continue gaining energy up to 10¹⁹ eV/nucleon and above.