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.     

Radio signals from extensive air showers with the energies <Emphasis Type="Italic">E</Emphasis> <Subscript>0</Subscript> ≥ 10<Superscript>19</Superscript> eV according to data from the Yakutsk extensive air shower array

A radio instrument and results obtained from the measurements of the 32-MHz radio signal from particles of extensive air showers (EASs) with energies E₀ ≥ 1×10¹⁹ eV are reported in brief. The data were obtained at the Yakutsk EAS array in 1987–1989 (the first series of measurements) and in 2009–2014 (new series of measurements). The radio signal from EASs with energies above 10²⁰eV was detected at the Yakutsk EAS array for the first time, including the shower with the record energy of ~2×10²⁰ eV for the Yakutsk EAS array.     

Astrophysical and structural peculiarities of extensive air showers with energy E 0 ≥ 1017 eV from Yakutsk EAS array data

The astrophysical characteristics of primary cosmic rays (PCRs) and the structure of extensive air showers (EASs) with energy E ₀ ≥ 10¹⁷ eV are simultaneously analyzed using the Yakutsk EAS array data acquired in the period 1974–2005. Enhanced and reduced particle fluxes are shown to come from the disk of the Supergalaxy (the Local Supercluster of galaxies) at E ₀ ≥ 5 × 10¹⁸ eV and E ₀ ≤ (2?3) × 10¹⁸, respectively. The development of air showers with E ₀ ≥ (3?5) × 10¹⁸ eV differs significantly from that at lower energies. This is interpreted as a manifestation of the possible interaction between extragalactic PCRs and the matter of this spatial structure.     

Radio emission from extensive air showers as a method for cosmic-ray detection

At the present time, radio emission from extensive air showers (EASs) is being considered as a new promising method for detecting cosmic rays of energy in the region E ₀ > 5 × 10¹⁶ eV. Radio emission from an EAS whose development is simulated by the Monte Carlo method is calculated here. The field of radio emission from an EAS is calculated on the basis of two representations of a shower: that as a set of individual particles and that as a continuous set of currents. The sensitivity of radio emission to EAS parameters in the frequency range 10–100 MHz is investigated. The results can be used to analyze experiments that being presently performed (CODALEMA and LOPES) and those that are being planned for the future.     

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.     

Electrons and muons in extensive air showers of energies E 0≥3×1017 eV: Yakutsk array data and QGSJET model

The results obtained from an analysis of the 1974–1998 Yakutsk array data on muons with threshold energy E _μ ≈ 1.0 × secθ GeV and on all charged particles (electrons and muons) in extensive air showers (EAS) are reported and compared with the results of calculations based on the model of quark-gluon strings with jets. For energies of E ₀≤3×10¹⁸ eV and zenith angles of θ≤45°, the results of the model calculations are consistent with the measured properties of the showers, while, for higher energy EASs, there are considerable discrepancies, which are probably due to the change in the development of the shower cascade in the region E ₀≥3×10¹⁸ eV.     

Macroscopic calculation of air shower radio emission

Two patterns of calculation of radio emission from extensive air showers (EAS), the so-called microapproach and macroapproach, are considered. The predictions of these approaches are compared by calculating the spatial distribution of the 40 MHz radio emission at the EAS energy 10¹⁶ eV.     

Spatio-temporal structure of the muon disk at <Emphasis Type="Italic">E</Emphasis><Subscript>0</Subscript> ≥ 5 × 10<Superscript>16</Superscript> eV from Yakutsk EAS array data

We present the results of our study of the temporal structure of the muon disk at the Yakutsk array in extensive air showers with primary energies E₀ ≥ 5 × 10¹⁶ eV at distances of 250–1500 m from the shower axis obtained using a large muon detector with an area of 184 m² and a detection threshold of E_μ ≈ 0.5 sec θ GeV. We have found two components with different muon disk thicknesses that require significant revisions of our view of the development of extensive air showers.     

Zenith-angle dependences of ρ s,600 and ρ μ,600, in giant air showers

Results of a global analysis of data from the Yakutsk array and AGASA are presented. The zenith-angle dependences ρ _s,600(θ) and ρ _μ,600(θ) of the densities of all charged particles and muons (the threshold energy is E _μ ≈ 1.0·secθ GeV) at a distance of 600 m from the axis of giant air showers (GAS) of energies E ₀≥10¹⁹ eV are considered. These dependences are compared with the results of the calculations based on the QGSJET model and performed for the case of primary protons. The results of the calculations within this model agree well with data from both arrays at E ₀≤2×10¹⁸ eV, but they are in a glaring contradiction with GAS data. The experiments indicate that the lateral structure of showers changes at E ₀≥(3–5)×10¹⁸ eV. In all probability this is due to some new processes accompanying their evolution. The neglect of this fact can lead to considerably overestimating the GAS energy (by a factor of 1.5–2.5).     

Energy Spectrum of Ultrahigh-Energy Cosmic Rays according to Data from Ground-Based Scintillation Detectors of the Yakutsk EAS Array

Results obtained from an analysis of the energy spectrum of cosmic rays with energies in the region of E₀ ≥ 10¹⁷ eV over the period of continuous observations from 1974 to 2017 are presented. A refined expression for estimating the primary-particle energy is used for individual events. This expression is derived from calculations aimed at determining the responses of the ground-based and underground scintillation detectors of the Yakutsk array for studying extensive air showers (EAS) and performed within theQGSJET-01-d, QGSJET-II-04, SIBYLL-2.1, and EPOS-LHCmodels by employing the CORSIKA code package. The new estimate of E₀ is substantially lower than its counterpart used earlier.     

Estimate of the mass composition of cosmic rays with E 0 ≤ 1018 eV according to the data from a new muon detector at the Yakutsk EAS array

The lateral distribution function of muons with the threshold E _μ ≈ 0.5secθ GeV (θ is the zenith angle) in extensive air showers with energy E ₀ ≥ 10¹⁷ eV has been examined using a new detector located at a distance of 180 m from the center of the Yakutsk array. This detector has been operating since autumn 2012 and consists of 27 autonomous scintillator counters with an area of 2 m². The experimental data have been compared to the calculations within the QGSJET-01 model with the CORSIKA air shower simulator. Agreement between the experimental data and calculations is achieved for the mixed composition of cosmic rays with the average atomic number satisfying the condition 〈lnA〉 ≈ 2.84 ± 0.08.     

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.     

Investigation of the structure of a muon disk for <Emphasis Type="Italic">E</Emphasis><Subscript>0</Subscript> ≥ 5 × 10<Superscript>16</Superscript> eV according to data of the Yakutsk array for studying extensive air showers

The results are presented that were obtained at the Yakutsk array by investigating the time structure of a muon disk in extensive air showers of primary energy in the region E ₀ ≥ 5 × 10¹⁶ eV at distances of 250 to 1500 m from the shower core. The measurements were performed with a large muon detector that has an area of 184 m² and a detection threshold of E _μ≈0.5secθ GeV and which began operating in November 1995. Two components having different muon-disk thicknesses were discovered, and this requires strong modifications in the currently prevalent idea of the development of extensive air showers. The problem of the existence of E ₀ ≥ 10²⁰ eV events is considered. __________ Translated from Yadernaya Fizika, Vol. 68, No. 1, 2005, pp. 74–88. Original Russian Text Copyright ? 2005 by Glushkov, Dedenko, Sleptsov.     

Depth of the maximum of extensive air showers and mass composition of primary cosmic radiation at an energy of 4 × 10<Superscript>17</Superscript> eV according to data on radioemission from extensive air showers

The results of a reanalysis of experimental data on extensive-air-shower radioemission that were obtained previously at the Moscow State University array for studying extensive air showers are presented. The lateral distribution of radioemission is given for showers characterized by a primary energy of 4 × 10¹⁷ eV and a zenith angle of θ = 35°. On the basis of an analysis of a lateral distribution of radioemission, the average value of the shower-maximum depth at a primary energy of 4 × 10¹⁷ eV is estimated at X _max = 655 ± 13 g/cm². Estimates of themass content of primary radiation that were obtained from an analysis of the distribution of X _max are compatible with the hypothesis that the role of light nuclei becomes more pronounced at energies above 10¹⁷ eV.     

On EAS spectrum with extremely low content of hadrons in the primary-energy range ∼10<Superscript>14</Superscript>−10<Superscript>15</Superscript> eV

The distribution of energy fluxes of the hadron component of extensive air showers through an ion-ization calorimeter in the primary-energy range ～3 × 10¹³?10¹⁶ eV is considered. Extensive air showers with zero and minimum energy fluxes of the hadron component are selected. It is concluded that the primary-energy range E ₀ ≈ 1 × 10¹⁴?2 × 10¹⁵ eV contains isotropic γ radiation with a spectrum close to bell-shaped, having a maximum near E ₀ ≈ 2.2 × 10¹⁴ eV and an additional peak near E ₀ ≈ 1.6 × 10¹⁵ eV.     

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.     

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.     

Low-frequency radio emission induced by the coherent magneto-bremsstrahlung of charged particles of an extensive air shower

A previously unknown coherent low-frequency (0<ν<50 kHz) component of radio emission of an extensive air shower in the geomagnetic field is reported. This type of emission induces a high-intensity field (∼200 μV/m MHz at a distance of 100 km from the shower axis). This emission mechanism is believed to be responsible for the previously observed high-intensity radio emission of the shower at low frequencies. The possibility of radio detection of ultrahigh-energy (W ₀>10²¹ eV) cosmic rays is considered.     

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.     

Muons in extensive air showers of energies E 0=1016.6–1019.8 eV

Data on muons with the threshold energy E _μ≈1.0×secθ GeV in extensive air showers of energies E ₀≥4×10¹⁶ eV measured on the Yakutsk and Akeno arrays are jointly analyzed. The results are compared with the calculations by the quark-gluon-string model with jets. It is shown that this model does not contradict the data measured for energies E ₀≤10¹⁸ eV on both arrays under the assumption that the primary particle composition differs from the composition where heavy nuclei dominate over protons. Experimental data for energies E ₀≥3×10¹⁸ eV indicate that the shower development differs from that predicted by the quark-gluon-string model with jets.