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.
|Original language||English (US)|
|Number of pages||4|
|Journal||Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics|
|State||Published - Jan 20 2012|
Bibliographical noteFunding Information:
The authors thank C. Dermer, J. Beacom, W. Essey, P. Mészáros, and S. Razzaque for discussions. A.K. and M.B.V. were supported in part by DOE grants DE-FG03-91ER40662 and DE-FG02-94ER40823 , respectively. The authors appreciate hospitality of the Aspen Center for Physics, supported by NSF grant 1066293 , where this work was done.