How well do we understand the properties of the Galactic cosmic ray accelerators and of cosmic ray propagation in the Galaxy ? A critical view.
July 06, 2021
The Galactic cosmic ray (CR) fluxes observed in the vicinity of the Earth encode
the space and time averaged properties of their sources and are also shaped
by the effects of their propagation in the Galaxy.
A combined study of the spectra of different particle types
(protons, primary and secondary nuclei, electrons, positrons and antiprotons)
is essential to determine the roles of the source and of propagation in the
formation of the fluxes.
Several authors are now claiming that these combined studies
have essentially solved the problem, and that the
properties of CR propagation, and the source spectra
for all particle types are now well determined in a broad energy range,
with significant uncertainties only at high energy.
In this contribution we analyse critically these results, and conclude
that the problem of determining in good approximation
the average CR source spectra
(and therefore also the main properties of CR propagation) remains open,
with very large uncertainties.
Solving this problem has profound implications for the properties of
the Galactic CR accelerators (that have not yet been firmly identified)
and for our understanding of the Milky Way magnetic structure.
Future observations, especially of electrons and positrons in the
multi-TeV range and of unstable isotopes like beryllium in the few GeV
range should soon allow to solve the problem.
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