A new model for the extragalactic gamma-ray background

Abstract

We present a two-parameter model of the extragalactic gamma-ray background (EGB) in the 0.1-100 GeV range as measured by the Large Area Telescope (LAT) onboard the Fermi satellite. The EGB can be fully explained as the sum of three distinct components, namely blazars, non-beamed AGNs (Seyfert galaxies and QSOs), and cosmic rays from star-forming galaxies. The contribution to the background from beamed sources is obtained by fitting the Fermi-LAT blazar differential number counts assuming that the gamma-ray luminosity function is directly proportional to the radio luminosity function of FRI and FRII galaxies. The high energy emission from non-beamed AGNs is instead determined by popular synthesis models of the observed X-ray background. Finally, the EGB is fit by adding a third component arising from pion decay in cosmic rays, assuming that such component is closely linked to the cosmic star formation history. We find that blazars dominate at energies \geq 10 GeV, for E \leq 0.2 GeV the main contribution is from non-beamed AGNs, while cosmic rays are required in between. Because of absorption due to interaction of gamma-rays with the extra-galactic background light, our model falls short at the highest energies probed by LAT, (\geq 70 GeV), leaving room to a possible contribution from dark matter particle annihilation. As an example, a particle of mass ~ 0.5 TeV and cross section <σv>~ 5*10^{-26} cm^3 s^-1 can accomodate the data.

5 pages, 3 figures, submitted to MNRAS

References in corpus (4)

• Components of the Extragalactic Gamma Ray Background
• The Contribution of Blazars to the Extragalactic Diffuse Gamma-ray Background and Their Future Spatial Resolution
• Current and Future Constraints on Dark Matter from Prompt and Inverse-Compton Photon Emission in the Isotropic Diffuse Gamma-ray Background
• Extragalactic Very-High-Energy gamma-ray background

Cited by in corpus (7)

• The Cosmological Impact of Luminous TeV Blazars I: Implications of Plasma Instabilities for the Intergalactic Magnetic Field and Extragalactic Gamma-Ray Background
• The nature of the Diffuse Gamma-Ray Background
• The Cosmological Impact of Luminous TeV Blazars III: Implications for Galaxy Clusters and the Formation of Dwarf Galaxies
• A Case for Radio Galaxies as the Sources of IceCube's Astrophysical Neutrino Flux
• Dissecting the Gamma-Ray Background in Search of Dark Matter
• Constraints on dark matter annihilations from diffuse gamma-ray emission in the Galaxy
• Lower Limits on the Anisotropy of the Extragalactic Gamma-Ray Background implied by the 2FGL and 1FHL Catalogs