The chemical composition of the cosmic radiation around the ankle and the related spectral indices

TL;DR

This paper models the chemical composition of cosmic radiation around the ankle energy, comparing theoretical predictions with experimental data, and finds good overall agreement except with some experiments like HiRes.

Contribution

It provides a quantitative calculation of cosmic ray composition from 10^12 to 5x10^19 eV using a two-component model and compares it with extensive experimental data.

Findings

Good agreement with data up to 2x10^19 eV, except HiRes.

Excellent match in the 10^15-10^17 eV range with several experiments.

Extradisc component flux at 10^19 eV is twice that of disc sources.

Abstract

Some recent measurements of the chemical composition of the cosmic radiation indicate that at the energy of 3 x 10 **18 eV, around the ankle, light cosmic ions dominate the spectrum as it occurs in the preknee energy region. Taking advantage of a recent theory of cosmic radiation which provides a quantitative explanation of the knee, the second knee and the ankle, the chemical composition of cosmic radiation is explicitly calculated giving individual ion spectra and ion fractions from 10 ** 12 eV to 5 x 10 ** 19 eV. The calculation assumes two components of the cosmic radiation feeding the ion flux at Earth: one originated in the disc volume and another one, called extradisc component, which from the disc boundaries traverses the Galaxy reaching the solar system. Data above 10 ** 17 eV collected during half century of experimentation by Auger, HiRes, Agasa, Akeno, Fly' s Eye, Yakutsk, Haverah Park and Volcano Ranch experiments are reviewed, examined and compared with the theoretical <ln(A)>. The comparison between computed and measured <ln(A)> exhibits a good global accord up to 2 x 10 ** 19 eV except with the HiRes experiment and an excellent agreement in the range 10 ** 15 - 10 ** 17 eV with Kascade, Eas-top, Tunka and other experiments. The accord requires a flux of the extradisc component of 1.8 x 10 ** 14 particles / m ** 2 sr s eV **(1.5) at 10 ** 19 eV, twice that generated by disc sources.