Gamma-ray emitting supernova remnants as the origin of Galactic cosmic
  rays?
  The origin of cosmic rays is one of the long-standing mysteries in physics
and astrophysics. Simple arguments suggest that a scenario of supernova
remnants (SNRs) in the Milky Way as the dominant sources for the cosmic ray
population below the knee could work: in a generic calculation, it can be shown
that these objects can provide the energy budget necessary to explain the
observed flux of cosmic rays. However, this argument is based on the assumption
that all sources behave in the same way, i.e.\ they all have the same energy
budget, spectral behavior and maximum energy. In this paper, we investigate if
a realistic population of SNRs is capable of producing the cosmic ray flux as
it is observed below the knee. We use 21 SNRs that are well-studied from radio
wavelengths up to gamma-ray energies. It could be shown previously (Mandelartz
& Becker Tjus 2015) that the high-energy bump in the energy spectrum of these
21 sources can be dominated by hadronic emission. Here, gamma-rays are produced
via $\pi^{0}-$decays from cosmic ray interactions in molecular clouds near the
supernova remnant, which serves as the cosmic ray accelerator. The cosmic ray
spectra show a large variety in their energy budget, spectral behavior and
maximum energy. These sources are assumed to be representative for the total
class of SNRs, where we assume that about 100 - 200 cosmic ray emitting SNRs
should be present today. Finally, we use these source spectra to simulate the
cosmic ray transport from individual SNRs in the Galaxy with the GALPROP code
for cosmic ray propagation. We find that the cosmic ray budget can be matched
well for a diffusion coefficient that is close to $D\propto E^{0.3}$. A
stronger dependence on the energy, e.g. $E^{0.5}$, would lead to a spectrum at
Earth that is too steep when compared to what is detected and the energy budget
cannot be matched, in particular toward high energies.
