L. W. Jones

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.

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.

Investigation of the main characteristics of the superhigh energy primary cosmic radiation in the GAMMA experiment (Mt. Aragats, Armenia)

The all-particle energy spectrum of the Primary Cosmic Radiation obtained from the data of GAMMA array (3200 m a.s.l., 700 g/cm2 of atmospheric depth) is presented. The results are obtained by the event-by-event method of the E0 -energy estimation which is developed using the EAS simulation with use of the software CORSICA and the SIBYLL interaction model with subsequent reconstruction of shower parameters taking into account the response of GAMMA detectors, reconstruction errors, as well as fluctuations of EAS development. By using this method an essential “bump”-shaped irregularity is observed in the all-particle spectrum at primary energies of ∼7.4×107 GeV; the bump exceeds a smooth power-law fit to the data by about 4 standard deviations. From the results of studies of the systematic uncertainties of our methods conclusion is made that the observed irregularity has a physical nature rather than is caused by methodical errors. A model explaining this phenomenon is proposed.