Extragalactic and galactic sources: New evidence, new challenges, new opportunities
1 Department of Physics and Astronomy, University of California, Los Angeles, CA 90095-1547, USA
2 Kavli IPMU, University of Tokyo, Kashiwa, Chiba 277-8568, Japan
a e-mail: firstname.lastname@example.org
Recent data bring in sharper focus the issue of relative contributions of galactic and extragalactic sources of ultrahigh-energy cosmic rays. On the one hand, there is some new evidence, from gamma-ray observations of blazars, that cosmic rays are, indeed, accelerated in AGNs. On the other hand, recent measurements of composition reported by Pierre Auger Observatory can be explained by a contribution of transient galactic sources, such as past GRBs and hypernovae, if nuclei accelerated in such events get trapped in the turbulent galactic magnetic fields. The likely contamination of UHECR data by the nuclei from past galactic stellar explosions creates new challenges for cosmic-ray astronomy. At the same time, it creates new opportunities for reconstructing galactic magnetic fields, understanding the history of transient galactic phenomena, and for using gamma rays to identify astrophysical nuclear accelerators outside Milky Way.
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