MEASUREMENT OF THE SPATIAL DISTRIBUTION OF DIFFUSE TeV GAMMA-RAY EMISSION FROM THE GALACTIC PLANE WITH MILAGRO

Diffuse gamma-ray emission produced by the interaction of cosmic-ray particles with matter and radiation in the Galaxy can be used to probe the distribution of cosmic rays and their sources in different regions of the Galaxy. With its large field of view and long observation time, the Milagro Gamma Ray Observatory is an ideal instrument for surveying large regions of the northern hemisphere sky and for detecting diffuse gamma-ray emission at very high energies. Here the spatial distribution and the flux of the diffuse gamma-ray emission in the TeV energy range with a median energy of 15 TeV for Galactic longitude between 30 degrees and 110 degrees and between 136 degrees and 216 degrees and for Galactic latitude between -10 degrees and 10 degrees are determined. The measured fluxes are consistent with predictions of the GALPROP model everywhere, except for the Cygnus region (l is an element of[65 degrees, 85 degrees]). For the Cygnus region, the flux is twice the predicted value. This excess can be explained by the presence of active cosmic-ray sources accelerating hadrons, which interact with the local dense interstellar medium and produce gamma rays through pion decay.