The Spectrum of the Isotropic Diffuse Gamma-Ray Emission Derived From
  First-Year Fermi Large Area Telescope Data
  We report on the first Fermi Large Area Telescope (LAT) measurements of the
so-called "extra-galactic" diffuse gamma-ray emission (EGB). This component of
the diffuse gamma-ray emission is generally considered to have an isotropic or
nearly isotropic distribution on the sky with diverse contributions discussed
in the literature. The derivation of the EGB is based on detailed modelling of
the bright foreground diffuse Galactic gamma-ray emission (DGE), the detected
LAT sources and the solar gamma-ray emission. We find the spectrum of the EGB
is consistent with a power law with differential spectral index g = 2.41+/-0.05
and intensity, I(> 100 MeV) = (1.03+/-0.17) 10^-5 cm^-2 s^-1 sr^-1, where the
error is systematics dominated. Our EGB spectrum is featureless, less intense,
and softer than that derived from EGRET data.
