Diffuse emission is the most prominent observational signature of the
GeV gamma-ray sky, and was established before individual gamma-ray
sources started to emerge. It became a prime source of knowledge about
cosmic-ray particle interactions and radiation processes at very high
energies. In contrast to the GeV domain, the search for diffuse emission
at TeV-energies is still in its infancy, largely due to the predominant
charged particle background that constitutes the principal instrumental
challenge for observational techniques. Diffuse emission is expected in
the TeV-domain too, on the Galactic scale primarily from the interaction
of protons and nuclei with the interstellar gas, and by Inverse Compton
scattering of high energy electron on the interstellar radiation field.
Local emission is also predicted in the vicinity of cosmic accelerators
in dense molecular clouds or locally enhanced radiation fields, the
emission being indicative for particle escape from their acceleration
region. A characterization of the phenomenon over the transition regime
from diffuse emission dominance to gamma-ray source dominance will be
made, emphasizing also consequences for observations and analysis
techniques with the upcoming Cherenkov Telescope Array.
|