Diffuse Gamma Rays of Extragalactic Origin

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Session 4 -- Gamma Ray Astrophysics
Display presentation, Wednesday, January 12, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[4.04] Diffuse Gamma Rays of Extragalactic Origin

P. Sreekumar, B. L. Dingus, J. A. Esposito (NASA/GSFC, USRA), D. L. Bertsch, C. E. Fichtel, R. C. Hartman, S. D. Hunter, F. W. Stecker, D. J. Thompson (NASA/GSFC), J. R. Mattox (NASA/GSFC, CSC), G. Kanbach, H. A. Mayer-Hasselwander, C. von Montigny (MPE), J. Chiang, Y. C. Lin, P. F. Michelson, P. L. Nolan, T. D. Willis (Stanford Univ.), and E. Schneid (Grumman), M. H. Salamon (Univ. of Utah)

{The all-sky survey in high energy gamma rays (E$>$30 MeV) carried out by EGRET aboard the Compton Observatory provides for the first time an opportunity to examine in detail diffuse gamma ray emission of extragalactic origin. The observed diffuse emission at high galactic latitudes is generally assumed to have a galactic component arising from cosmic ray interactions with the local interstellar gas and radiation, in addition to an isotropic extragalactic component. Using a model calculation of the galactic component, EGRET observations of the high latitude emission are used to examine the flux and spectrum of the extragalactic emission. These results will be compared with previous estimates from the SAS-2 experiment (Thompson \& Fichtel, 1982).

Bignami, Fichtel, Hartman and Thompson (1979), showed that it was plausible that active galaxies could account for the extragalactic diffuse radiation. Recently, Stecker, Solomon, and Malkan (1993) have estimated the blazar component of the extragalactic diffuse radiation based on flat spectrum radio source studies. At MeV energies, a component from matter-antimatter annihilation (Stecker 1985) may also exist. An improved version of these models will be compared to the recent EGRET observations.}

\vskip 0.1in \noindent{Thompson \& Fichtel, 1982, A\&A, 109, 352} \goodbreak \noindent{Bignami, Fichtel, Hartman \& Thompson, 1979, ApJ 232, 649} \goodbreak \noindent{Stecker, Solomon, \& Malkan, 1993, ApJ 410, L71} \goodbreak \noindent{Stecker, 1985, Nuc.Phys.B 252, 25}

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