Abstract
The search for the sources of high-energy cosmic rays (CRs) has made significant progress the past decade. By including multimessenger methods, the general picture of the presence of a Galactic component at low energies and an extragalactic one at the highest energies has been strengthened. Yet, unambiguous proof of the exact origins of CRs is missing. In this review, the current scientific status on Galactic CR sources from theory and experimental data is summarized. In particular, the focus of this review lies on the search for photon and neutrino signals from the Galaxy and their theoretical interpretation in the context of the quest for the origin of high-energy cosmic rays. The use of multiwavelength data, from radio to TeV energies, as well as the option of coincident observations of different wavelength bands in order to pin-point the sources of Galactic CRs are discussed. Finally, the objectives for the field of astroparticles to reach the goal of unambiguously identifying Galactic cosmic ray sources within the next decades are presented.
Highlights
During recent years, the search for the sources of highenergy cosmic rays (CRs) has made large progress
In contrast to the analysis described above, where all neutrino flavors are included, but applying strong selection criteria, the search for point sources focusses on the large number of muon-neutrinos that interact via charged current interactions – IceCube detects approximately 200 neutrino-induced muons per day, most of which are of atmospheric origin [70]
The multimessenger approach has proven itself as an extremely valuable tool to move towards the identification of the sources of Galactic CRs: major progress has been made with charged CRs, photons and neutrinos, summarized here, with an outlook for the potential of development of the field given in the same context:
Summary
The search for the sources of highenergy cosmic rays (CRs) has made large progress. While the energy spectrum itself is quite well measured, the concrete sources could not be pin-pointed yet due to the diffusion of CRs through Galactic (and extragalactic) magnetic fields. The multimessenger approach in the search for the origins of CRs builds on including all available information from charged CRs as well as from neutral secondaries that are produced near the sources through hadronic interactions. The final, neutral particles, neutrinos ν and photons γ carry approximately 5%, respectively 10% of the original CR energy and point back to their sources directly. The focus lies on presenting the state of the art concerning multimessenger searches for Galactic CRs. Central arguments for supernova remnants (SNRs) as the main contributing source class will be presented The paper concludes with an outlook for the prospects of identifying the concrete sources of Galactic CRs in the decades (Sect. 4)
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