The Fermi-LAT high-latitude Survey: Source Count Distributions and the Origin of the Extragalactic Diffuse Background

A. A. Abdo , Markus Ackermann , Marco Ajello , E. Antolini , Luca Baldini , Jean Ballet (1) , Guido Barbiellini , D. Bastieri , B. M. Baughman , K. Bechtol , R. Bellazzini , B. Berenji , R. D. Blandford , E. D. Bloom , E. Bonamente , A. W. Borgland , A. Bouvier , J. Bregeon , A. Brez , M. Brigida , Pascal Bruel (2) , T. H. Burnett , S. Buson , G. A. Caliandro , R. A. Cameron , P. A. Caraveo , S. Carrigan , J. M. Casandjian (1) , E. Cavazzuti , C. Cecchi , O. Celik , E. Charles , A. Chekhtman , C. C. Cheung , J. Chiang , S. Ciprini , R. Claus , J. Cohen-Tanugi (3) , J. Conrad , L. Costamante , S. Cutini , C. D. Dermer , A. de Angelis , F. de Palma , E. Do Couto E Silva , P. S. Drell , R. Dubois , D. Dumora (4) , C. Farnier (3) , C. Favuzzi , S. J. Fegan (2) , W. B. Focke , Y. Fukazawa , S. Funk , P. Fusco , F. Gargano , D. Gasparrini , N. Gehrels , S. Germani , N. Giglietto , P. Giommi , F. Giordano , T. Glanzman , G. Godfrey , I. A. Grenier (1) , J. E. Grove , S. Guiriec , D. Hadasch , M. Hayashida , E. Hays , S. E. Healey , D. Horan (2) , R. E. Hughes , R. Itoh , G. Johannesson , A. S. Johnson , T. J. Johnson , W. N. Johnson , T. Kamae , H. Katagiri , J. Kataoka , N. Kawai , Jürgen Knödlseder (5) , M. Kuss , J. Lande , L. Latronico , S.-H. Lee , M. Lemoine-Goumard (4) , M. Llena Garde , F. Longo , F. Loparco , B. Lott (4) , M. N. Lovellette , P. Lubrano , G. M. Madejski , A. Makeev , M. N. Mazziotta , W. Mcconville , J. E. Mcenery , C. Meurer , P. F. Michelson , W. Mitthumsiri , T. Mizuno , C. Monte , M. E. Monzani , A. Morselli , I. V. Moskalenko , S. Murgia , P. L. Nolan , J. P. Norris , E. Nuss (3) , T. Ohsugi , N. Omodei , E. Orlando , J. F. Ormes , M. Ozaki , D. Paneque , J. H. Panetta , D. Parent (4) , V. Pelassa (3) , M. Pepe , M. Pesce-Rollins , F. Piron (3) , T.A. Porter , S. Raino , R. Rando , M. Razzano , A. Reimer , O. Reimer , S. Ritz , L. S. Rochester , A. Y. Rodriguez , R. W. Romani , M. Roth , H. F.-W. Sadrozinski , A. Sander , P. M. Saz Parkinson , J. D. Scargle , C. Sgro , M. S. Shaw , P. D. Smith , G. Spandre , P. Spinelli , Jean-Luc Starck , M. S. Strickman , A. W. Strong , D. J. Suson , H. Tajima , H. Takahashi , T. Takahashi , T. Tanaka , J. B. Thayer , J. G. Thayer , D. J. Thompson , L. Tibaldo (1) , D. F. Torres , G. Tosti , A. Tramacere , Y. Uchiyama , T. L. Usher , V. Vasileiou , N. Vilchez (5) , V. Vitale , A. P. Waite , P. Wang , B. L. Winer , K. S. Wood , Z. Yang , T. Ylinen , M. Ziegler

1 AIM (UMR7158 / UMR_E_9005 / UM_112) - Astrophysique Interprétation Modélisation
2 LLR - Laboratoire Leprince-Ringuet
3 LPTA - Laboratoire de Physique Théorique et Astroparticules
4 CENBG - Centre d'Etudes Nucléaires de Bordeaux Gradignan
5 CESR - Centre d'étude spatiale des rayonnements

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.

Mots clés: cosmology: observations; diffuse radiation; galaxies: active; galaxies: jets; gamma rays: diffuse background; surveys

Domaines: Phénomènes cosmiques de haute energie [astro-ph.HE]; Phénomènes cosmiques de haute energie [astro-ph.HE]

A. A. Abdo, Markus Ackermann, Marco Ajello, E. Antolini, Luca Baldini, et al.. The Fermi-LAT high-latitude Survey: Source Count Distributions and the Origin of the Extragalactic Diffuse Background. The Astrophysical Journal, 2010, 720, pp.435-453. ⟨10.1088/0004-637X/720/1/435⟩. ⟨in2p3-00530044⟩