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The 2009 Fermi Symposium

Extragalactic Diffuse

Markus Ackermann, SLAC


The Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope provides tremendous advances in studying the high-energy diffuse gamma-ray emission at energies between 100 MeV and >300 GeV. Its large field-of-view of 2.4 sr and its peak effective area of >0.8 m2, combined with a sky-survey observation strategy, allow for an almost uniform exposure of the whole sky with unprecedented statistics. The diffuse emission observed by the Fermi LAT is a superposition of several components. A highly structured Galactic component arising from the interactions of cosmic rays with the interstellar gas and radiation is dominant at low Galactic latitudes. The target of this study is an additional isotropic component which is commonly attributed to be of extragalactic origin. We present an analysis of the flux and spectrum of the extragalactic diffuse gamma-ray emission observed by the LAT, based on detailed modeling and subtraction of foreground contributions from the LAT point sources, the Galactic diffuse and solar system emission as well as residual contamination by cosmic rays.