Abstract
The isotropic diffuse γ-ray background (IGRB) has been detected by various experiments and recently the Fermi-LAT Collaboration has precisely measured its spectrum in a wide energy range. The origin of the IGRB is still unclear and we show in this paper the significative improvements that have been done, thanks to the new Fermi-LAT catalogs, to solve this mystery. We demonstrate that the γ-ray intensity and spectrum of the IGRB is fully consistent with the unresolved emission from extragalactic point sources, namely Active Galactic Nuclei and Star Forming Galaxies. We show also that the IGRB can be employed to derive sever constraints for the γ-ray emission from diffuse processes such as annihilation of Dark Matter (DM) particles. Our method is able to provide low bounds for the thermal annihilation cross section for a wide range of DM masses.
Highlights
The existence of an isotropic component in the γ-ray sky has been observed since 1972 by the OSO-3 satellite [1]
Since the Large Area Telescope (LAT) has detected more than 3000 sources in four years of operation [3], the most obvious explanation for the solution of this puzzle is that the IGRB arises from the emission of unresolved, i.e. undetected, point sources
Since Active Galactic Nuclei (AGNs), Star Formign Galaxies (SFGs) and pulsars are detected by Fermi-LAT at |b| > 20◦, we expect that these source populations should largely contribute to the IGRB intensity
Summary
The existence of an isotropic component in the γ-ray sky has been observed since 1972 by the OSO-3 satellite [1]. Since Active Galactic Nuclei (AGNs), Star Formign Galaxies (SFGs) and pulsars are detected by Fermi-LAT at |b| > 20◦, we expect that these source populations should largely contribute to the IGRB intensity.
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