Results from the GAMMA experiment on Mt. Aragats

TL;DR

The GAMMA experiment on Mt. Aragats studied cosmic rays above the knee, revealing a variable power-law spectrum and irregularities around 70-80 PeV, supporting a two-component model including pulsar-origin Fe components.

Contribution

This paper provides new measurements of cosmic ray composition and spectrum above the knee, highlighting spectral irregularities and supporting a two-component primary cosmic ray model.

Findings

The energy spectrum becomes flatter above 20 PeV.

Irregularities observed at 70-80 PeV suggest additional components.

A two-component model with pulsar Fe contributions explains the spectrum features.

Abstract

The present status of the GAMMA facility consisting of an enlarged surface EAS array (116 of 1 m^2 scintillation detectors) and underground muon carpet (150 m^2 detectors) is described. The recent results on mass composition and energy spectrum at the energy region above the knee obtained on the basis of the GAMMA experimental data are presented. It is shown that the power law after the knee is not invariable like -3.1. The slope of the energy spectrum becomes more flat at E0>20 PeV. The strong irregularities of the energy spectrum at about 70-80 PeV are discussed in comparison with other experiments. The bump can be described by a two-component model of primary cosmic ray origin, where additional (pulsar) Fe components are included with a very flat power law energy spectrum.