Nearby sources in the transition region between Galactic and Extragalactic cosmic rays

TL;DR

This paper interprets the spectral features of cosmic rays between the knee and ankle, attributing them mainly to Galactic sources like Type Ia SNRs and suggesting an extragalactic origin above 10^17 eV, supported by spectral analysis and candidate source evaluation.

Contribution

It presents a model explaining the spectral structure of cosmic rays in the transition region, emphasizing the role of Type Ia SNRs and analyzing the potential contribution of Galactic sources like Cas A.

Findings

Residual cosmic ray flux shows a knee at 2-3×10^17 eV.

Spectral slopes are approximately 1.8 below and 3.4 above the knee.

Extragalactic origin of cosmic rays is favored starting from 10^17 eV.

Abstract

In this paper, a probable interpretation of a remarkable fine structure of all particle spectra between the knee and the ankle, as well as a high content of heavy nuclei around 10^17 eV measured recently in Tunka-133 and KASCADE Grande experiments, is presented in the model where production of cosmic rays in Type Ia SNRs provides observed cosmic rays (CR) flux around the knee. Subtracting the contribution of these sources from all particle spectrum we obtained the residual flux of CR in the transition region between Galactic and Extragalactic CR in the range 10^17-5 10^18 eV. The obtained spectrum also has a pronounced knee at energy (2-3)10^17 eV and slopes g1 ~ 1.8+-0.3 below it and g2 ~3.4 above it. We analyzed the possible contribution from known Galactic sources and found that formally the best candidate to contribute significantly to the transition region is Cas A. This source posses a number of unusual properties and considered as Type IIb SNR. However we showed that the hypothesis of extragalactic origin of CR starting from 10^17 eV seems more realistic.