Intermediate-mass and heavy Galactic cosmic-ray nuclei: The case of new AMS-02 measurements

The recent measurement of the spectra of intermediate-mass nuclei and iron nuclei carried out with the AMS-02 experiment provided us with the most complete set of data on cosmic-ray fluxes to date, and allowed us to test the standard model for the transport of these particles through the Galaxy to the finest details. We show that the parameters derived from lighter primary and secondary elements in the cosmic radiation also lead to a good description of the data on heavier nuclei, with no need to invoke different injection spectra for such nuclei, provided the whole chain of fragmentation is properly accounted for. The only exception to this finding is represented by iron nuclei, which show a very unusual trend at rigidity less than or similar to 100 GV. This trend reflects in a Fe/O ratio that is at odds with the results of the standard model of cosmicray transport, and is in contradiction with data collected by HEAO, ACE-CRIS and Voyager at lower energy. We speculate on possible origins of such findings.

Automated summary

Recent measurements of cosmic-ray fluxes by the AMS-02 experiment have provided a comprehensive set of data, showing that parameters derived from lighter elements can effectively describe heavier nuclei data. The only anomaly is observed in iron nuclei at rigidity less than 100 GV, contradicting the standard model and previous data collections.