Rigidity-dependent cosmic ray energy spectra in the knee region obtained with the GAMMA experiment

On the basis of the extensive air shower (EAS) data obtained by the GAMMA experiment, the energy spectra and elemental composition of the primary cosmic rays are derived in the 1-100 PeV energy range. The reconstruction of the primary energy spectra is carried out using an EAS inverse approach in the framework of the SIBYLL2.1 and QGSJET01 interaction models and the hypothesis of power-law primary energy spectra with rigidity-dependent knees. The energy spectra of primary H, He, O-like and Fe-like nuclei obtained with the SIBYLL interaction model agree with corresponding extrapolations of the balloon and satellite data to ~1 PeV energies. The energy spectra obtained from the QGSJET model show a predominantly proton composition in the knee region. The rigidity-dependent knee feature of the primary energy spectra for each interaction model is displayed at the following rigidities: ~2.5+/-0.2 PV (SIBYLL) and ~3.1-4.2 PV (QGSJET). All the results presented are derived taking into account the detector response, the reconstruction uncertainties of the EAS parameters, and fluctuations in the EAS development.Comment: 28 pages, 18 figures, accepted for publication in Astroparticle Physic

Energy spectra and elemental composition of primary nuclei in the knee region: Recent results from the GAMMA experiment

On the basis of the extensive air shower (EAS) data obtained by the GAMMA experiment, the energy spectra and elemental composition of the primary cosmic rays are derived in the 1–100 PeV energy range. The reconstruction of the primary energy spectra is carried out using an EAS inverse approach with the hypothesis of power-law primary energy spectra with rigidity-dependent knees. The rigidity-dependent knee feature of the primary energy spectra is displayed at the rigidities ER ~= 2.5±0.2 PeV/Z and ER ~= 3.1–4.2 PeV/Z for the SIBYLL and QGSJET interaction models respectively. Using the event-by-event method of the primary energy evaluation from the measured Nch, Nμ and shower age (s) parameters, the all-particle energy spectrum is also obtained

Search for high-energy gamma-ray emissionand upgrade of the GAMMA experiment on Mt. Aragats

We present the current status of the search for possible diffuse orlocalized gamma-ray emission at energies above about 100 TeV with the GAMMA air shower detector which is located at 3200 m a.s.l. on Mt. Aragats, Armenia. For this search we select muon-poor extensive air showers detected by GAMMA.We discuss ongoing studies of improved criteria for the selection ofmuon-poor showers, taking into account the geometry of the muon underground detector array in 2004–2011. A modernization of the muon array was completed between October 2011 and February 2012. Sixty additional muon scintillation detectors were installed and are now taking data. They will improvethe the selection of muon-poor showers, the primary energy estimation, and should also yield improved information on the mass composition