Limitations on the photo-disintegration process as a source of VHE photons

We consider whether photo-disintegration is ever able to provide an effective mechanism for the production of VHE γ-ray emission from astrophysical sources. We find that the efficiency of this process is always smaller by a factor A/Z2 (∼4/A) than that of nuclei cooling through Bethe–Heitler pair-production. Furthermore, for sources optically thin to TeV emission, we find that the efficiency of this process can be no more than 3 × 10−5(Rsource/RLarmor), where Rsource is the source size and RLarmor is the CR nuclei Larmor radius. We conclude that this process is unable to provide an effective mechanism for VHE γ-ray emission from astrophysical sources.

Research highlights
► Efficiency of cosmic ray cooling processes in a radiation field.
► Pressures on the cosmic ray luminosity placed by low efficiency processes.
► Relationships between the efficiency of cosmic ray cooling processes and the parameters describing astrophysical sources.