The GeV-TeV Connection in Galactic γ-Ray Sources

Recent observations with atmospheric Cerenkov telescope systems such as H.E.S.S. and MAGIC have revealed a large number of new sources of very high energy (VHE) γ-rays from 100 GeV to 100 TeV, mostly concentrated along the Galactic plane. At lower energies (100 MeV to 10 GeV) the satellite-based instrument EGRET revealed a population of sources clustering along the Galactic plane. Given their adjacent energy bands, a systematic correlation study between the two source catalogs seems appropriate. Here, the populations of Galactic sources in both energy domains are characterized on observational as well as on phenomenological grounds. Surprisingly few common sources are found in terms of positional coincidence and spectral consistency. These common sources and their potential counterparts and emission mechanisms are discussed in detail. In cases of detection in only one energy band, for the first time consistent upper limits in the other energy band have been derived. The EGRET upper limits are rather unconstraining due to the sensitivity mismatch to current VHE instruments. The VHE upper limits put strong constraints on simple power-law extrapolation of several of the EGRET spectra and thus strongly suggest cutoffs in the unexplored energy range from 10 to 100 GeV. Physical reasons for the existence of cutoffs and for differences in the source population at GeV and TeV energies are discussed. Finally, predictions are derived for common GeV-TeV sources for the upcoming GLAST mission, bridging for the first time the energy gap between current GeV and TeV instruments.

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