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Diffuse Gamma Rays of Galactic and Extragalactic Origin: Preliminary Results from EGRET

Published online by Cambridge University Press:  25 May 2016

P. Sreekumar  and
D.A. Kniffen
P. Sreekumar
Affiliation:
NASA/Goddard Space Flight Center (USRA), Greenbelt, MD 20771, USA
D.A. Kniffen
Affiliation:
Hampden-Sydney College, Hampden-Sydney, VA 23943, USA

Abstract

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The all-sky survey in high energy gamma rays (E>30 MeV) carried out by the Energetic Gamma Ray Experiment Telescope (EGRET) aboard the Compton Gamma Ray Observatory provides for the first time an opportunity to examine in detail diffuse gamma-ray emission of extra-galactic 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 component presumably of extragalactic origin. The galactic component can be estimated from a model of the interstellar medium and cosmic-ray distribution. Since the derived extragalactic spectrum depends very much on the success of our galactic model, the consistency of the galactic diffuse emission model is examined both spectrally and spatially with existing EGRET observations. In conjunction with this model, EGRET observations of the high latitude emission are used to examine the flux and spectrum of the residual extragalactic emission. This residual emission could be either truly diffuse in origin or could arise from accumulated emission from unresolved sources particularly in the light of EGRET observations showing the presence of numerous gamma-ray bright active galactic nuclei.

Type
Part I: Invited Reviews
Information
Symposium - International Astronomical Union , Volume 168: Examining the Big Bang and the Diffuse Background Radiations , 1996 , pp. 279 - 288
Copyright
Copyright © Kluwer 1996 

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