Very-high-energy gamma-ray signal from nuclear photodisintegration as a probe of extragalactic sources of ultrahigh-energy nuclei

It is crucial to identify the ultrahigh-energy cosmic-ray sources and probe their unknown properties. Recent results from the Pierre Auger Observatory favor a heavy nuclear composition for the ultrahigh-energy cosmic rays. Under the requirement that heavy nuclei survive in these sources, using gamma-ray bursts as an example, we predict a diagnostic gamma-ray signal, unique to nuclei—the emission of deexcitation gamma rays following photodisintegration. These gamma rays, boosted from MeV to TeV-PeV energies, may be detectable by gamma-ray telescopes such as VERITAS, HESS, and MAGIC, and especially the next-generation CTA and AGIS. They are a promising messenger to identify and study individual ultrahigh-energy nuclei accelerators.