The cosmic diffuse gamma-ray background
measured with COMPTEL
G. Weidenspointner, M. Varendorff, R. Diehl, G.G. Lichti, V. Schönfelder
H. Bloemen, W. Hermsen
We report an independent and refined analysis of the cosmic diffuse
gamma-ray background (hereafter CDG) in the energy range 0.8-30 MeV
with the Compton telescope COMPTEL onboard the Compton Gamma-Ray
Observatory. This analysis extends earlier work on the extrapolation
method, using improved instrumental-background treatment and more
data. We have identified all major instrumental-background lines and
included the results of a detailed study of the instantaneous
instrumental continuum-background characteristics. Furthermore, we
used all available COMPTEL data at high galactic latitudes, rather
than only those from the Virgo region and the south Galactic pole.
The new ``whole-sky'' average CDG spectrum again shows no evidence for
an MeV-bump, merges smoothly with the spectra at higher and lower
energies, and is consistent with a transition from a softer to a
harder component around a few MeV. This spectrum is consistent with
previous COMPTEL results from the Virgo region and all-sky model
fitting analysis within statistical and systematic uncertainties. In
addition, comparison of the CDG intensity from various regions of the
sky allows us to place limits on the large-scale anisotropy of the CDG
in selected energy bands. Upper limits on the relative deviations from
isotropy consistent with the data at the 95% confidence limit range
from about 24% to about 45% on scales of a few steradian.
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On 16 Jul 1999, 09:19.