TeV γ-rays from nuclei photodissociation: the case of Cygnus OB2

We investigate astrophysical contexts where TeV 7-rays can result from the photo-de-excitation of PeV cosmic ray nuclei after their parents have undergone photodissociation in an environment of ultraviolet photons. This process is proposed as a candidate explanation of the recently discovered HEGRA source at the edge of the core of the Cygnus OB2 association. The Lyman-a background is provided by the rich O and B stellar environment. The HEGRA flux results if there is efficient acceleration at the source of lower energy nuclei. The requirement that the Lorentz-boosted ultraviolet photons reach the Giant Dipole Resonant energy (∼ 20 MeV) implies a strong suppression of the γ-ray spectrum compared to an E-2γ behavior at energies below ∼ 1 TeV (some of these energies will be probed by the upcoming GLAST mission)