Recent observations by atmospheric Cherenkov telescopes such as H.E.S.S., and MAGIC have revealed a large number of new sources of very-high-energy (VHE) gamma-rays above 100 GeV, mostly concentrated along the Galactic plane. At lower energies (100 MeV - 10 GeV) the satellite based instrument EGRET revealed a population of gamma-ray sources clustering along the Galactic Plane. Here we investigate those gamma-ray sources, which currently lack a connection in their adjacent energy band. We conclude on similarities and differences among the EGRET resp. VHE gamma-ray sources, and complement the discussion with consistently determined upper limits in their proximate energy band. An interpretation will invoke characteristics of known object classes at high-energy gamma-rays, and both observational and theoretical arguments to explain situations where no counterpart can be expected in one or the other energy regimes.

Proceedings of the 30th International Cosmic Ray Conference; Rogelio Caballero, Juan Carlos D'Olivo, Gustavo Medina-Tanco, Lukas Nellen, Federico A. Sánchez, José F. Valdés-Galicia (eds.); Universidad Nacional Autónoma de México, Mexico City, Mexico, 2008; Vol. 2 (OG part 1), pages 613-616