Implication of multiple source populations of Galactic cosmic rays from proton and helium spectra

Complicated hardenings and softenings of the spectra of cosmic ray protons and helium have been revealed by the newest measurements, which indicate the existence of multiple source populations of Galactic cosmic rays. We study the physical implications of these results in this work. A phenomenological fitting shows that three components can properly give the measured structures of the proton and helium spectra. The data are then accounted for in a physically motivated, spatially-dependent propagation model. It has been shown that one background source population plus two local sources, or two background source populations plus one local source can well reproduce the measurements. The spectral structures of individual species of cosmic rays are thus natural imprints of different source components of cosmic rays. Combined with ultra-high-energy $\gamma$-ray observations of various types of sources, the mystery about the origin of Galactic cosmic rays may be uncovered in future.