Constraints on the VHE Emissivity of the Universe from the Diffuse GeV Gamma-Ray Background

摘要: VHE (Very High Energy, E>100 GeV) radiation emitted at cosmological distances will pair produce on low-energy diffuse extragalactic background before ever reaching us. This prevents us from directly seeing most of the emission in Universe. However, a gamma-ray that produces initiates an electromagnetic cascade. At low energies, this secondary cascade has spectrum insensitive to primary gamma-radiation and, unlike original radiation, IS observable. Motivated by new measurements MeV-GeV background, we discuss constraints placed source populations requiring they not exceed observed levels. We use new, accurate cascading code and pay particular attention dependence cosmic infrared/optical wavelengths. Despite considerable uncertainty find robust may still be integrated emissivity potential sources The limits are tighter than those obtained considering microwave alone restrict significantly, for example, parameter space available exotic particle physics scenarios recently proposed explain highest energy ray events. If direct blazar AGN fact accounts GeV these strengthen rule out which significant power above 300 GeV.