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A gamma-ray signature of energetic sources of cosmic-ray nuclei |
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| Authors: | Alexander Kusenko M.B. Voloshin |
| Affiliation: | a Department of Physics and Astronomy, University of California, Los Angeles, CA 90095-1547, USA b IPMU, University of Tokyo, Kashiwa, Chiba 277-8568, Japan c William I. Fine Theoretical Physics Institute, University of Minnesota, Minneapolis, MN 55455, USA d Institute of Theoretical and Experimental Physics, Moscow, 117218, Russia |
| Abstract: | Astrophysical sources of nuclei are expected to produce a broad spectrum of isotopes, many of which are unstable. An unstable nucleus can beta-decay outside the source into a single-electron ion. Heavy one-electron ions, thus formed, can be excited in their interactions with cosmic microwave background photons, in which case they relax to the ground state with the emission of a gamma ray. Repetitive cycles of excitation and gamma-ray emission can produce an observable feature in the gamma-ray spectrum with a maximum around 8 GeV (for iron). We find that the observed spectrum of Centaurus A is consistent with a substantial flux of nuclei accelerated to 0.1 EeV. A characteristic 5-10 GeV (iron) shoulder in the gamma-ray spectra of various sources can help identify astrophysical accelerators of nuclei or set upper limits on nuclear acceleration. |
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