Closing in on the origin of Galactic cosmic rays using multimessenger
  information
  In cosmic ray physics extensive progress has been made in recent years, both
concerning theory and observation. The vast details in direct, indirect and
secondary detections on the one hand provide the basis for a detailed modeling
of the signatures via cosmic-ray transport and interaction, paving the way for
the identification of Galactic cosmic-ray sources. On the other hand, the large
number of constraints from different channels of cosmic-ray observables
challenges these models frequently.
  In this review, we will summarize the state-of-the art of the detection of
cosmic rays and their secondaries, followed by a discussion what we can learn
from coupling our knowledge of the cosmic-ray observables to the theory of
cosmic-ray transport in the Galactic magnetic field. Finally, information from
neutral secondaries will be added to draw a multimessenger-picture of the
non-thermal sky, in which the hypothesis of supernova remnants as the dominant
sources survives best. While this has been known since the 1930s, evidence for
this scenario is steadily growing, with the first detection of hadronic
signatures at GeV energies detected for three SNRs with Fermi. The existence of
SNRs as PeVatrons, however, is not validated yet. The discussion of this and
other open questions concerning the level of anisotropy, composition and
spectral shape of the cosmic-ray energy spectrum is reviewed. Future
perspectives of how to find the smoking cosmic-ray source gun concludes this
review.
