Sharp knee phenomenon of primary cosmic ray energy spectrum

TL;DR

This paper investigates the sharp knee feature in the primary cosmic ray energy spectrum between 1 and 200 PeV, supporting a two-component origin model involving pulsar and galactic sources, and tests non-linear shock acceleration models.

Contribution

It introduces and tests a two-component spectral model and non-linear diffusive shock acceleration models against extensive air shower data in the knee region.

Findings

Supports a two-component origin of the knee spectrum involving pulsar and galactic fluxes.

Finds that non-linear DSA models fit observed spectra with specific cutoff rigidities.

Confirms H-He primary nuclei as the main contributors to the spectral knee.

Abstract

Primary energy spectral models are tested in the energy range of 1-200 PeV using standardized extensive air shower responses from BASJE-MAS, Tibet, GAMMA and KASCADE scintillation shower arrays. Results point towards the two-component origin of observed cosmic ray energy spectra in the knee region (GAPS spectral model) consisting of a pulsar component superimposed upon rigidity-dependent power law diffuse galactic flux. The two-component energy spectral model accounts for both the sharp knee shower spectral phenomenon and observed irregularity of all-particle energy spectrum in the region of 50-100 PeV. Alternatively, tested multi-population primary energy spectra predicted by non-linear diffusive shock acceleration (DSA) models describe observed shower spectra in the knee region provided that the cutoff magnetic rigidities of accelerating particles are 6.0+/-0.3 PV and 45+/-2 PV for the first two populations respectively. Both tested spectral models confirm the predominant H-He primary nuclei origin of observed shower spectral knee. The parameters of tested energy spectra are evaluated using solutions of inverse problem on the basis of the corresponding parameterizations of energy spectra for primary H, He, O-like and Fe-like nuclei, standardized shower size spectral responses in the 550-1085 g/cm^2 atmospheric slant depth range and near vertical muon truncated size spectra detected by the GAMMA array.