The Cosmic Diffuse Gamma-Ray Spectrum
The COMPTEL CDG flux measurements in the 1 to 10 MeV range are about
5-10 times lower than the pre-COMPTEL estimates. The CDG measurements
show no evidence of the MeV bump in the 1 to 10 MeV range. The
integrated flux from 0.8 to 9 MeV is (4.7 ± 1.7) x 10^-3
photons/cm^2-s-sr and that from 9 to 30 MeV is (1.5 ± 0.3) x 10^-4
photons/cm^2-s-sr. This represents the first significant detection
(statistical significance of 7.2 sigma) of the CDG emission in the 9
to 30 MeV range. The preliminary COMPTEL CDG estimates reported
earlier (Kappadath et al. 1995; 1996; 1997) are in good agreement with
these results.
The COMPTEL CDG spectrum is fit to power-law function, A x (E/E0)^-a,
where A is the flux normalization, E is the photon energy, E0 is taken
to be 5 MeV (the logarithmic-midpoint energy between 0.8 and 30 MeV)
and a is the spectral index. The resulting differential photon
spectrum from 800 keV to 30 MeV is well described by a photon spectral
index of -2.4 ± 0.2 and a flux normalization of (1.05 ± 0.2) x
10^-4 photons/cm^2-s-sr-MeV at 5 MeV.
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