Understanding galactic cosmic rays

The case is made for most cosmic rays having come from galactic sources. ‘Structure’, i.e. a lack of smoothness in the energy spectrum, is apparent, strengthening the view that most cosmic rays come from discrete sources, supernova remnants being most likely.

• Gamma-ray astronomy gives evidence of the galactic origin of CR at GeV energies. • CR energy spectrum indicates the non-uniform space–time distribution of CR sources. • Galactic supernova remnants (SNRs) are the most likely source of CR up to PeV energies. • High density of SNR in the inner galaxy creates flatter energy spectrum than locally.