1150 articles – 4007 references  [version française]
 HAL: in2p3-00530044, version 1
 arXiv: 1003.0895
 Astrophysical Journal 720 (2010) 435-453
 The Fermi-LAT high-latitude Survey: Source Count Distributions and the Origin of the Extragalactic Diffuse Background
 For the Fermi-LAT collaboration(s)
 (2010-09-01)
 This is the first of a series of papers aimed at characterizing the populations detected in the high-latitude sky of the {\it Fermi}-LAT survey. In this work we focus on the intrinsic spectral and flux properties of the source sample. We show that when selection effects are properly taken into account, {\it Fermi} sources are on average steeper than previously found (e.g. in the bright source list) with an average photon index of 2.40$\pm0.02$ over the entire 0.1--100\,GeV energy band. We confirm that FSRQs have steeper spectra than BL Lac objects with an average index of 2.48$\pm0.02$ versus 2.18$\pm0.02$. Using several methods we build the deepest source count distribution at GeV energies deriving that the intrinsic source (i.e. blazar) surface density at F$_{100}\geq10^{-9}$\,ph cm$^{-2}$ s$^{-1}$ is 0.12$^{+0.03}_{-0.02}$\,deg$^{-2}$. The integration of the source count distribution yields that point sources contribute 16$(\pm1.8)$\,\% ($\pm$7\,\% systematic uncertainty) of the GeV isotropic diffuse background. At the fluxes currently reached by LAT we can rule out the hypothesis that point-like sources (i.e. blazars) produce a larger fraction of the diffuse emission.
 1: Astrophysique Interactions Multi-échelles (AIM) CNRS : UMR7158 – INSU – Université Paris VII - Paris Diderot – CEA : DSM/IRFU 2: Laboratoire Leprince-Ringuet (LLR) CNRS : UMR7638 – IN2P3 – Polytechnique - X 3: Laboratoire de Physique Théorique et Astroparticules (LPTA) CNRS : UMR5207 – IN2P3 – Université Montpellier II - Sciences et techniques 4: Centre d'Etudes Nucléaires de Bordeaux Gradignan (CENBG) CNRS : UMR5797 – IN2P3 – Université Sciences et Technologies - Bordeaux I 5: Centre d'étude spatiale des rayonnements (CESR) CNRS : UMR5187 – Observatoire Midi-Pyrénées – INSU – Université Paul Sabatier [UPS] - Toulouse III
 Subject(s) : Physics/Astrophysics/High Energy Astrophysical PhenomenaSciences of the Universe/Astrophysics/High Energy Astrophysical Phenomena
 Keyword(s): cosmology: observations – diffuse radiation – galaxies: active – galaxies: jets – gamma rays: diffuse background – surveys