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.     

On special features of the longitudinal development of extensive air showers and on the spectrum of cosmic rays

It is shown that, in the development of an extensive air shower (EAS) initiated by primary cosmic rays in the Earth’s atmosphere, there is a special feature that sterms from the violation of equilibrium between EAS components and whose inclusion requires revising both EAS phenomenology and the existing experimental data obtained by indirectly measuring the energy spectrum of cosmic rays by the EAS method.     

Problem of the energy spectrum of ultrahigh-energy cosmic rays

A number of cosmic-ray energy spectra measured in the energy region E ₀ ≥ 10¹⁷ eV at the Yakutsk array and at AGASA, Haverah Park, HiRes, Auger, and SUGAR within different periods of time were considered. It was shown that, upon rescaling the energy of these spectra by factors of K = 0.75, 0.85, 0.9, 1.02, 1.19, and 1.29, respectively, all of them agree with one another rather well in shape. The factors K themselves exhibit a pronounced north-south dependence on the geographical latitude of the positions of the above arrays.     

The light nuclei energy spectrum of primary cosmic rays using EAS MSU array data

The change in the energy spectrum index Δγ in the knee region was determined by means of analysis of extensive air showers (EAS) spectra using the number of the particles measured by the EAS MSU array. The value was equal to 1.00 ± 0.12. A comparison of lightweight nuclei energy spectra collected with different installations was carried out.     

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.     

Incoherent microwave radiation of an extensive air shower

Incoherent radiation of relativistic electrons (positrons) of an extensive air shower in the ultrahigh energy range (～10 GHz) has been studied. The method of the division of an electron track into coherent segments has been used to estimate the power of a radio signal and to determine the radiation pattern. Comparison of the signal with radio noise of an antenna has shown that this radiation can be detected by modern engineering instruments and applied to detect ultrahigh-energy cosmic particles.     

The search for ultrashort bursts of cosmic ray intensity on the Andyrchi air shower array

A new data acquisition system that makes it possible to measure the count rate of each detector of the Andyrchi air shower array every millisecond is described. This new detection system allows us to search for ultrashort bursts of cosmic ray intensity when operating the array in the single-component detection mode. The method of data acquisition and analysis is discussed.     

On the energy spectrum of light nuclei in primary cosmic rays

The energy spectrum of primary protons and α particles has been determined from analysis of the EAS MSU array data. The result of the analysis is compared with the corresponding data from other arrays.     

Integral energy spectrum of primary cosmic rays at high energies

The integral energy spectrum of primary cosmic rays has been obtained. In the energy range (2.4×10³−1.1×10⁵ GeV), the spectrum of all nuclei is consistent with a power law of indexγ=1.55±0.06 and the flux of all nuclei is:N(⩾E ₀)⋍(5.1±1.8)×10⁻¹×E ₀ ^−1.55 particles/cm² sterad. sec., whereE ₀ is in GeV. The spectrum of primaryα-particles in the energy range (4.4×10³−4.8×10⁴) GeV is also consistent with a power law of indexγ=1.71±0.12 and the flux is:N(⩾E ₀)=(4.2±1.4)×10⁻¹×E ₀ ^−1.71 , particles per cm² sterad. sec, whereE ₀ is in GeV.     

Neutron “thunder” accompanying an extensive air shower

The role of the neutron component of extensive air showers at PeV and EeV energies is considered. The occurrence of neutrons delayed by several hundreds of microseconds with respect to the main shower front is explained by the production and slowing down of neutrons, mainly in the neutron monitor, when a PeV-EAS core falls on it, as well as in the nearby soil and environment. An important circumstance in study of EeV EASs is that neutrons form the dominant hadronic component at a distance of about 1 km from the EAS core and at delays about 5 μs with respect to the main shower front and may contribute to the signal of the detectors located at such distances.     

Radio-frequency component of transient radiation of an extensive air shower

The mechanism of radio emission induced by the transient radiation of oppositely charged particles from an extensive air shower in the geomagnetic field was studied for the first time. For showers with an energy of ∼10²² eV, the electric field strength at a distance of 500 km from the shower axis was found to be 60 μV/mMHz. Such showers attain their maximum at sea level. The spectral intensity of emission is maximum at frequencies of about 1 MHz (at these frequencies, the intensity of atmospheric disturbances is minimum). These specific features of radio emission can be used in experiments for radio detection of high-energy cosmic rays. An experimental setup of such detection is suggested.     

On the geomagnetic mechanism of the radiation of an extensive air shower

The radiation field of the elementary particles of an extensive air shower in the geomagnetic field has been examined. According to the solutions of Maxwell’s equation for an electron (positron) taking into account ionization losses, the radiation of the shower is determined only by the bremsstrahlung and geomagnetic mechanism. The Cherenkov component of radiation is almost absent.     

Yakutsk EAS array data on the variations in intensities of the highest energy cosmic rays

The results of analysis of arrival frequency of cosmic rays with energies E ₀≥4×10¹⁷ eV are presented based on the data collected on the Yakutsk array during its 24 years of continuous operation (1977–2000). It is shown that the intensity of cosmic rays is variable. At E ₀≤(3?5)×10¹⁸ eV, the (2–3)-month data show many deviations by (3–4)σ from the mean level. At E ₀≥10¹⁹ eV, the intensities steadily decrease, on the average, by 1.5 times during the time period considered.     

Estimation of the energy of the electron-photon component of cosmic rays on the basis of data for Cherenkov light from ultrahigh-energy extensive air showers

The energy fraction E _em/E ₀ dissipated to the electron-photon component of extensive air showers (EASs) for E ₀=10¹⁵?10¹⁹ eV is estimated using data on Cherenkov radiation and charged particles from the Yakutsk EAS array. The results are compared with models with different dissipations to the electron-photon component and with calculations for various primary nuclei. In the energy range 10¹⁵?10¹⁶ eV and 10¹⁸?10¹⁹ eV, the ratio E _em/E ₀ is equal to 77 ± 2 and 88 ± 2, respectively, in agreement with the mixed and proton contents of primary cosmic rays in the former and latter energy ranges, respectively.     

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.     

Low-energy break in the spectrum of Galactic cosmic rays

Measurements of the low-energy spectrum of Galactic cosmic rays (GCRs) by detectors on or near Earth are affected by solar modulation. To overcome this difficulty, we consider nearby molecular clouds as GCR detectors outside the Solar System. Using γ-ray observations of the clouds by the Fermi telescope, we derive the spectrum of GCRs in the clouds from the observed γ-ray emission spectrum. We find that the GCR spectrum has a low-energy break with the spectral slope hardening by ΔΓ=1.1±0.3 at an energy of E=9±3 GeV. Detection of a low-energy break enables a measurement of GCR energy density in the interstellar space U=0.9±0.3 eV/cm{3}.     

Possible origin and spectrum of ultrahigh-energy cosmic rays

The complicated form of the cosmic-ray spectrum recorded in the energy range 10¹⁷–10²⁰ eV by giant detector arrays is analyzed. It is shown that the spectrum in the region 10¹⁸–10¹⁹ eV is apparently identical to the injection spectrum with power-law exponent approximately equal to 3.2–3.3. The flat component in the region (3.2–5)×10¹⁹ eV is due to the braking of extragalactic protons by relict photons. The spectrum apparently has no blackbody cutoff at energies above 3.2×10¹⁹ eV. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 10, 729–733 (25 May 1997)