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 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.

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Source ISSN: 0004-637X
Author Ackermann, Markus, Ajello, Marco, Allafort, A., Asano, K., Atwood, W.B., Baldini, Luca, Ballet, Jean, Barbiellini, Guido, Bastieri, D., Bechtol, K., Bellazzini, R., Bloom, E.D., Bonamente, E., Borgland, A.W., Bottacini, E., Brandt, T.J., Bregeon, J., Brigida, M., Bruel, Pascal, Buehler, R., Burnett, T.H., Busetto, G., Buson, S., Caliandro, G.A., Cameron, R.A., Caraveo, P. A., Casandjian, J.M., Cecchi, C., Charles, E., Chaty, S., Chekhtman, A., Cheung, C.C., Chiang, J., Cillis, A.N., Ciprini, S., Claus, R., Cohen-Tanugi, J., Colafrancesco, S., Conrad, J., Cutini, S., d'Ammando, F., de Palma, F., Dermer, C.D., Silva, E.D.E., Couto, Do, Drell, S., Drlica-Wagner, A., Dubois, R., Favuzzi, C., Fegan, S.J., Ferrara, E.C., Focke, W.B., Fukazawa, Y., Funk, S., Fusco, P., Gargano, F., Gasparrini, D., Gehrels, N., Germani, S., Giglietto, N., Giordano, F., Giroletti, M., Glanzman, T., Godfrey, G., Grandi, P., Grenier, I.A., Grove, J.E., Guiriec, S., Hadasch, D., Hayashida, M., Hays, E., Horan, D., Hou, X., Hughes, R.E., Jackson, M.S., Jogler, T., Jóhannesson, G., Johnson, R.P., Johnson, A.S., Kamae, T., Kataoka, J., Kerr, M., Knödlseder, Jürgen, Kuss, M., Lande, J., Larsson, S., Latronico, L., Lavalley, C., Lee, S.H., Longo, F., Loparco, F., Lott, B., Lovellette, M.N., Lubrano, P., Mazziotta, M.N., Mcconville, W., Mcenery, J.E., Mehault, J., Michelson, P.F., Mignani, R.P., Mitthumsiri, W., Mizuno, T., Moiseev, A.A., Monte, C., Monzani, M.E., Morselli, A., Moskalenko, I.V., Murgia, S., Naumann-Godo, M., Nemmen, R., Nishino, S., Norris, J.P., Nuss, E., Ohsugi, T., Omodei, N., Orienti, M., Orlando, E., Ormes, J.F., Paneque, D., Panetta, J.H., Pelassa, V., Perkins, J.S., Pesce-Rollins, M., Pierbattista, M., Piron, F., Pivato, G., Poon, H., Porter, T.A., Rainò, S., Rando, R., Razzano, M., Razzaque, S., Reimer, A., Reimer, O., Reyes, L.C., Ritz, S., Rochester, L.S., Romoli, C., Roth, M., Sanchez, D.A., Saz Parkinson, P.M., Scargle, J.D., Sgrò, C., Siskind, E.J., Snyder, A., Spandre, G., Spinelli, P., Stephens, T.E., Suson, D.J., Tajima, H., Takahashi, H., Tanaka, T., Thayer, J.G., Thompson, D.J., Tibaldo, L., Tibolla, O., Tinivella, M., Tosti, G., Troja, E., Usher, T.L., Vandenbroucke, J., Vasileiou, V., Vianello, G., Vitale, V., von Kienlin, A., Waite, A.M., Wallace, E., Weltevrede, P., Winer, B.L., Wood, K.S., Wood, M., Zimmer, S.
Maintainer CCSD
Last Updated May 11, 2026, 03:01 (UTC)
Created May 11, 2026, 03:01 (UTC)
Identifier in2p3-00823282
Language en
contributor Astrophysique Interprétation Modélisation (AIM (UMR7158 / UMR_E_9005 / UM_112)) ; Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS)
creator Ackermann, Markus
date 2013-05-11T00:00:00
harvest_object_id bb4982b8-169c-4f83-91ce-844b241805f3
harvest_source_id 3374d638-d20b-4672-ba96-a23232d55657
harvest_source_title test moissonnage SELUNE
metadata_modified 2026-02-04T00:00:00
relation info:eu-repo/semantics/altIdentifier/arxiv/1309.5416
set_spec type:ART