Determination of the Point-spread Function for the Fermi Large Area Telescope from On-orbit Data and Limits on Pair Halos of Active Galactic Nuclei

Markus Ackermann , Marco Ajello , A. Allafort , K. Asano , W.B. Atwood , Luca Baldini , Jean Ballet (1) , Guido Barbiellini , D. Bastieri , K. Bechtol , R. Bellazzini , E.D. Bloom , E. Bonamente , A.W. Borgland , E. Bottacini , T.J. Brandt , J. Bregeon , M. Brigida , Pascal Bruel (2) , R. Buehler , T.H. Burnett , G. Busetto , S. Buson , G.A. Caliandro , R.A. Cameron , P. A. Caraveo , J.M. Casandjian (1) , C. Cecchi , E. Charles (3) , S. Chaty , A. Chekhtman , C.C. Cheung , J. Chiang , A.N. Cillis , S. Ciprini , R. Claus , J. Cohen-Tanugi , S. Colafrancesco , J. Conrad , S. Cutini , F. d'Ammando , F. de Palma , C.D. Dermer , E.D.E. Silva , Do Couto , S. Drell , A. Drlica-Wagner , R. Dubois , C. Favuzzi , S.J. Fegan (2) , E.C. Ferrara , W.B. Focke , Y. Fukazawa , S. Funk , P. Fusco (4) , F. Gargano (4) , D. Gasparrini , N. Gehrels , S. Germani , N. Giglietto , F. Giordano (4) , M. Giroletti , T. Glanzman , G. Godfrey , P. Grandi , I.A. Grenier , J.E. Grove , S. Guiriec , D. Hadasch , M. Hayashida , E. Hays , D. Horan (2) , X. Hou (5) , R.E. Hughes , M.S. Jackson , T. Jogler , G. Jóhannesson , R.P. Johnson , A.S. Johnson , T. Kamae , J. Kataoka , M. Kerr , Jürgen Knödlseder , M. Kuss , J. Lande , S. Larsson , L. Latronico , C. Lavalley , S.H. Lee , F. Longo , F. Loparco (4) , B. Lott (5) , M.N. Lovellette , P. Lubrano , M.N. Mazziotta (4) , W. Mcconville , J.E. Mcenery , J. Mehault (6) , P.F. Michelson , R.P. Mignani , W. Mitthumsiri , T. Mizuno , A.A. Moiseev , C. Monte , M.E. Monzani , A. Morselli , I.V. Moskalenko , S. Murgia , M. Naumann-Godo , R. Nemmen , S. Nishino , J.P. Norris , E. Nuss (6) , T. Ohsugi , N. Omodei , M. Orienti , E. Orlando , J.F. Ormes , D. Paneque , J.H. Panetta , V. Pelassa , J.S. Perkins , M. Pesce-Rollins , M. Pierbattista (1) , F. Piron (6) , G. Pivato , H. Poon , T.A. Porter , S. Rainò , R. Rando , M. Razzano , S. Razzaque , A. Reimer , O. Reimer , L.C. Reyes , S. Ritz , L.S. Rochester , C. Romoli , M. Roth , D.A. Sanchez , P.M. Saz Parkinson , J.D. Scargle , C. Sgrò , E.J. Siskind , A. Snyder , G. Spandre , P. Spinelli , T.E. Stephens , D.J. Suson , H. Tajima , H. Takahashi , T. Tanaka , J.G. Thayer , D.J. Thompson , L. Tibaldo , O. Tibolla , M. Tinivella , G. Tosti , E. Troja , T.L. Usher , J. Vandenbroucke , V. Vasileiou (6) , G. Vianello , V. Vitale , A. von Kienlin , A.M. Waite , E. Wallace , P. Weltevrede , B.L. Winer , K.S. Wood , M. Wood , S. Zimmer

1 AIM (UMR7158 / UMR_E_9005 / UM_112) - Astrophysique Interprétation Modélisation
2 LLR - Laboratoire Leprince-Ringuet
3 CSIRO - Commonwealth Scientific and Industrial Research Organisation [Canberra]
4 INFN, sezione di Bari - Istituto Nazionale di Fisica Nucleare, sezione di Bari
5 GLAST
6 LUPM - Laboratoire Univers et Particules de Montpellier

The Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope is a pair-conversion telescope designed to detect photons with energies from ≈20 MeV to >300 GeV. The pre-launch response functions of the LAT were determined through extensive Monte Carlo simulations and beam tests. The point-spread function (PSF) characterizing the angular distribution of reconstructed photons as a function of energy and geometry in the detector is determined here from two years of on-orbit data by examining the distributions of γ rays from pulsars and active galactic nuclei (AGNs). Above 3 GeV, the PSF is found to be broader than the pre-launch PSF. We checked for dependence of the PSF on the class of γ-ray source and observation epoch and found none. We also investigated several possible spatial models for pair-halo emission around BL Lac AGNs. We found no evidence for a component with spatial extension larger than the PSF and set upper limits on the amplitude of halo emission in stacked images of low- and high-redshift BL Lac AGNs and the TeV blazars 1ES0229+200 and 1ES0347-121.

Mots clés: galaxies: active; galaxies: halos; gamma rays: galaxies; instrumentation: detectors; intergalactic medium

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

Markus Ackermann, Marco Ajello, A. Allafort, K. Asano, W.B. Atwood, et al.. Determination of the Point-spread Function for the Fermi Large Area Telescope from On-orbit Data and Limits on Pair Halos of Active Galactic Nuclei. The Astrophysical Journal, 2013, 765, pp.54. ⟨10.1088/0004-637X/765/1/54⟩. ⟨in2p3-00823282⟩