Galactic Gamma Ray Background from Interactions of Cosmic Rays

Abstract: Various studies firmly establish the fact that gamma-ray observations can act as a unique probe to detect the possible cosmic ray (CR) sources, study the CR density distribution and explore the average properties of interstellar medium (ISM) such as the gas density profile of ISM. We use the DRAGON code to study different propagation models by incorporating realistic source distribution, Galactic magnetic field (GMF) and gas density profile, and finally obtain the proton distribution (both spatial and energy) in the Galaxy by fitting the locally observed CR spectra. The uncertainties in the model parameters used to study the CR propagation are also shown here. Our obtained proton distribution is then used to calculate the diffuse gamma-ray flux produced by proton-proton interactions in the Galactic halo. We compare our diffuse gamma-ray fluxes with the previous results and the isotropic gamma-ray background (IGRB) at sub -TeV energy regime measured by \textit{Fermi}-LAT. It is found to be much less than IGRB, which suggests IGRB is mostly of extragalactic origin. Finally, we use our obtained proton distribution to calculate gamma-ray fluxes from individual Galactic Molecular Clouds (GMCs) and those fluxes are compared with the \textit{Fermi}-LAT observations of GMCs.