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.     

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.     

Direct stratospheric measurements of charges and energies of Primary Cosmic Rays in the range of 10<Superscript>13</Superscript> − 10<Superscript>15</Superscript> eV (CROSS Project)

The CROSS (Cosmic Rays Over Spectrum Steepening) experiment is aimed at direct measurements of masses and energies of primary cosmic ray (PCR) nuclei in the range of 10¹³ ? 10¹⁵ eV near the break in the PCR energy spectrum. The experimental equipment includes a balloon ionization spectrometer consisting of X-ray transition radiation generators interlaid with thin-wall proportional chambers.     

Investigation of primary cosmic rays at energies above 10<Superscript>14</Superscript> eV

A search for sources of primary cosmic rays at energies of 10¹⁴–10¹⁵ eV was performed using the special independent KLARA+Khronotron unit at the Tien Shan Mountain Cosmic Ray Station in a joint experiment of the Lebedev Physics Institute (LPI) and the Central Research Institute for Physics (KFKI). A full data bank of standard events, consisting of 30 million extensive air showers (EASes), was analyzed. Analysis results are presented as maps of the directions of EAS arrival in equatorial coordinates in which the standard deviation of the number of events exceeds a certain value. These could be directions from which neutral primary cosmic particles (e.g., gamma ray photons) arrive from sources of primary cosmic rays. A match is found between separate directions with results, obtained on other stations, and the location of pulsars.     

A DEDUCTION ON PRIMARY COSMIC PAY COMPOSITION AND SPECTRA ABOVE 1014eV

The spectra of primary cosmic ray nuclei are fitted from experimental data under 10¹⁴eV and extrapolated to their bending energies. The primary cosmic ray composition above 10¹⁴eV is deduced according to the rigidity cut off model by selecting an appropriate bending energy for proton so that the sum of various nucleus components is consistent with the experimental total particle spectrum. The method used is independent on the behaviour of hadronic interaction.     

Description of a cosmic ray jet in terms of the two-centre model

A cosmic ray jet with primary energy about 10¹³ eV and its secondary interactions have been investigated in order to make a comparison with the predictions of the alternative variants of the two-centre model of particle emission.     

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.     

Ultrahigh-energy cosmic rays: Possible origin and spectrum

The complicated shape of the cosmic ray spectrum recorded by giant arrays in the energy range 10¹⁷–10²⁰ eV is analyzed. It is shown that in the energy region ∼10¹⁸–10¹⁹ eV the spectrum probably coincides with the injection spectrum whose exponent is equal approximately to 3.2–3.3. The flatter component in the energy region (3.2–5.0)×10¹⁹ eV is due to braking of extragalactic protons on primordial photons (the cosmic background radiation). At energies exceeding 3.2×10¹⁹ eV the spectrum does not have a blackbody cutoff. The possibility of determining the distances at which cosmic rays originate and investigating the evolution of their sources on the basis of ultrahigh-energy cosmic ray data is discussed. Zh. éksp. Teor. Fiz. 113, 12–20 (January 1998)     

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.     

Rising Inelastic Cross Section and its Contribution to Steepening of the Cosmic Ray Energy Spectrum

Calculations have been carried out to investigate the contribution of an increasing total cross section to steepening of the cosmic ray energy spectrum at very high energies (E ? 10¹² eV). Our results suggest that increasing total cross section contributes only a part to the steepening of primary energy spectrum at very high energies even if the composition is pure primary iron flux.     

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.     

Estimating the fraction of gamma quanta in the primary cosmic ray flux with energies of ∼1017 eV from the MSU EAS array data

Using data from the MSU EAS array and model calculations, we search for events with abnormally small fractions of muons with energies above 10 GeV in showers with particle numbers of >2 × 10⁷ and zenith angles of <30 degrees. We confirm with good statistical accuracy that the content of gamma quanta in the primary cosmic ray flux can be as high as 2% at energies of ～10¹⁷ eV.     

Acceleration of ultra-high energy cosmic rays by galaxy cluster accretion shocks

Acceleration of protons and nuclei by shock waves arising during accretion on galaxy clusters is considered. The generation of magnetohydrodynamic turbulence by streaming instability of accelerated particles in a shock precursor, cluster mass distribution, and particle energy loss upon interaction with cosmic microwave background and IR background radiation are taken into account. The contribution of these sources to the cosmic ray intensity observed at energies of 10¹⁷–10²⁰ eV is calculated.     

Some recent developments in cosmic rays

Recent work on the energy spectrum, composition and anisotropy of the primary cosmic ray flux from about 10⁹ eV to 10²⁰ eV is summarized, together with related information on phonons between 1 MeV and 200 MeV. Solar particles are not discussed, the emphasis being on topics bearing on the origin of the radiation, which is still an unsolved problem, although the probabilities are strongly in favour of an entirely galactic origin for the particles. Mechanisms of acceleration are not discussed.     

High-energy cosmic rays: Puzzles,models, and giga-ton neutrino telescopes

The existence of cosmic rays of energies exceeding 10²⁰ eV is one of the mysteries of high-energy astrophysics. The spectrum and the high energy to which it extends rule out almost all suggested source models. The challenges posed by observations to models for the origin of high-energy cosmic rays are reviewed, and the implications of recent new experimental results are discussed. Large area high-energy cosmic ray detectors and large volume high-energy neutrino detectors currently under construction may resolve the high-energy cosmic ray puzzle, and shed light on the identity and physics of the most powerful accelerators in the Universe.     

Local anisotropy of cosmic rays with <Emphasis Type="Italic">E</Emphasis><Subscript>0</Subscript> ≥ 10<Superscript>17</Superscript> eV from Yakutsk EAS array data

The arrival directions of primary cosmic ray particles with energies E ₀ ≥ 10¹⁷ eV and zenith angles θ ≤ 60° recorded on the Yakutsk array over the period 1974–2009 are analyzed. These events are shown to have different anisotropies in different energy ranges.     

The cosmic ray boron and carbon isotopic composition measured in nuclear emulsions

A study is made of the isotopic composition of primary cosmic ray boron and carbon in the energy interval 135–390 MeV/n. The quotients¹¹B/(¹⁰B +¹¹B) = 0.61 ±0.12 and¹³C/(¹²C +¹³C) = 0.06 ±0.04, valid at the top of the atmosphere, are obtained from photometric measurements on tracks found in an Ilford G5 emulsion stack exposed to the radiation.     

Peculiarities of the anisotropy of cosmic rays with E0 ≥ 1019 eV from Yakutsk EAS array data

The arrival directions of primary cosmic ray particles with energies E ₀ ≥ 10¹⁹ eV and zenith angles θ ≤ 60° recorded on the Yakutsk array over the period 1974–2009 are analyzed. These events separated by different time intervals are shown to have different global anisotropies.     

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.

     

Testing the correlations between ultrahigh-energy cosmic rays and BL Lac-type objects with HiRes stereoscopic data

Previously suggested correlations of BL Lac-type objects with the arrival directions of the ultrahigh-energy cosmic ray primaries are tested by making use of the HiRes stereoscopic data. The results of the study support the conclusion that BL Lacs may be cosmic ray sources and suggest the presence of a small (a few percent) fraction of neutral primaries at E > 10¹⁹ eV.