R.M. Martirosov

An all-particle primary energy spectrum in the 3–200 PeV energy range

We present an all-particle primary cosmic-ray energy spectrum in the 3 × 10 6 – 2 × 10 8 GeV energy range obtained by a multi-parametric event-by-event evaluation of the primary energy. The results are obtained on the basis of an expanded EAS data set detected at mountain level (700 g cm −2 )b y the GAMMA experiment. The energy evaluation method has been developed using the EAS simulation with the SIBYLL interaction model taking into account the response of GAMMA detectors and reconstruction uncertainties of EAS parameters. Nearly unbiased (<5%) energy estimations regardless of a primary nuclear mass with an accuracy of about 15–10% in the 3 × 10 6 –2 × 10 8 GeV energy range respectively are attained. An irregularity (‘bump’) in the spectrum is observed at primary energies of ∼7.4 × 10 7 GeV. This bump exceeds a smooth power-law fit to the data by about 4 standard deviations. By not rejecting the stochastic nature of the bump completely, we examined the systematic uncertainties of our methods and conclude that they cannot be responsible for the observed feature.

Aragats space-environmental centre: status and SEP forecasting possibilities

The Aragats Space Environment Center in Armenia provides real-time monitoring of cosmic particle fluxes. Neutron monitors operating at altitudes of 2000 m and 3200 m on Mt Aragats continuously gather data to detect possible abrupt enhancement of the count rates. Additional high precision detectors, measuring muon and electron fluxes, along with directional information have been put in operation on Mt Aragats in the summer of 2002. We plan to use this information to establish an early warning system against extreme solar energetic particle (SEP) events which pose danger to the satellite electronics and the space station crew. Solar ion and proton fluxes as measured by space-borne sensors on ACE and GOES satellites are used to derive expected arrival times of highest energy ions at 1 AU. The peaks in the time series detected by Aragats neutron monitors, coincided with these times, demonstrate the possibility of early detection of SEP events using the ground-based detectors.

The cosmic ray energy spectrum around the knee measured with the GAMMA array at Mt. Aragats

Experimental data on EAS characteristics with Ne > 10 5 are used to calculate the so-called αe-parameter which is directly connected with the energy of the primary cosmic ray radiation. It is shown that the distribution of showers selected by a constant value of this parameter is isotropic, and the measurement of the αe-spectrum is a direct way to obtain the primary energy spectrum. Using the αe-parameter, the primary all-particle energy spectrum of the cosmic radiation in the knee region is obtained. The energy spectrum is compared with th ec orresponding data of other experiments.

EAS electron and muon distributions and size spectra from the GAMMA installation

The phenomenological characteristics of the electron and muon components of extensive air showers with the range 105≤Ne≤107 are obtained from the GAMMA installation of the ANI experiment at Mt Aragats in Armenia at an observation level of 700 g cm-2. The experimental results are compared with other experiments and with the simulation carried out using the CORSIKA code and ARES package.

Fine structure of all-particle energy spectrum in the knee region

All-particle energy spectrum in the knee region obtained from extensive air shower (EAS) measurements (GAMMA experiment, 700 g/cm2, Armenia) is presented. Energies of primary particles in the range of 106–108 GeV were evaluated on the basis of observed shower parameters Nch,Nμ, s, θ and corresponding parameterisation of CORSIKA simulated database for SIBYLL interaction model. All shower detection and reconstruction uncertainties were included in the simulated showers for four kinds (H, He, O, Fe) of primary nuclei. The reliability of observed all-particle energy spectrum is investigated from viewpoint of methodical errors and statistical fluctuations. Observed fine structure of all-particle energy spectrum can be interpreted by the rigidity-dependent steepening Galactic diffuse nuclei flux and an additional iron component in the region of 70-80 PeV primary energies most likely originated from nearby pulsars.

Properties of the difference method for searching for anisotropy of primary cosmic rays

Methodical properties and features of the original difference method for searching for the anisotropy in the knee region of the primary cosmic ray energy spectrum are analyzed. It is shown that the method in which properties of particle fluxes, rather than intensities, are studied is stable to randomexperimental errors andmakes it possible to separate anomalies associatedwith the laboratory coordinate system from anomalies in the celestial coordinates. The method uses multiple scattering of charged particles in galactic magnetic fields for studying the entire celestial sphere, including sky regions beyond the installation line of sight.

The response of the EAS muon component in the GAMMA installation

Abstract The response of the EAS muon component is studied by the detector simulation program ARES developed for the GAMMA experiment on Mt. Aragats (ANI Cosmic Ray Observatory, Armenia). Comparisons of experimental data with predictions of detector response simulations on the muon lateral distribution and the distribution of the muon size are presented.

Behaviour of the EAS electron-photon and muon component characteristics in the knee region at mountain altitudes

Abstract The characteristics of the EAS electron-photon and muon components in showers with given sizes 105 ≤ Ne ≤ 107 are obtained by the GAMMA installation at the Mt. Aragats (Armenia, 700 g/cm2. The analysis of data was carried out having in mind the different explanations about the nature of the knee.

Experimental check of the new method of selection of EAS with constant energies at observation level 700 g/cm2

The experimental data obtained in the new EAS experiment Gamma at Mt. Aragats (Armenia) allows to select showers generated by primaries with different masses but with the same primary energy. Such a selection gives the possibility to estimate the primary mass composition for given energies by much more simple and precise way. In this work, the recent experimental data obtained with the help of Gamma array are compared with the Tien Shan results. An excellent agreement is shown, which confirms our Monte Carlo calculations, carried out for EAS muon and electrons components.