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ADS Astronomy Abstract Service

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 Title:              COMPTEL measurements of the Cosmic Diffuse Gamma-Ray
                     Spectrum from 800 keV to 30 MeV
 Authors:            KAPPADATH, S.C.; RYAN, J.; MCCONNELL, M.;
                     BENNETT, K.; WINKLER, C.; BLOEMEN, H.; HERMSEN, W.;
                     DIEHL, R.; SCHONFELDER, V.; VARENDORFF, M.;
                     WEIDENSPOINTNER, G.
 Affiliation:        AA(U. New Hampshire), AD(Astrophysics Div., ESTEC, The
                     Netherlands), AF(SRON-Utrecht, The Netherlands),
                     AH(MPE-Garching, Germany)
 Journal:            Bull. American Astron. Soc., 192, #70.03
 Publication Date:   05/1998
 Origin:             AAS
 Abstract Copyright: (c) 1998: American Astronomical Society
 Bibliographic Code: 1998AAS...192.7003K

                                  Abstract

We report on the Cosmic Diffuse Gamma Ray (CDG) spectrum from 800 keV to 30
MeV obtained with the Imaging Compton telescope COMPTEL, on-board the
Compton Gamma Ray Observatory. The spectrum is constructed by measuring the
count rate of gamma rays from high galactic latitudes during periods when
the Earth is outside the COMPTEL field-of-view. Special data selections are
applied to suppress the prompt and delayed background contributions. Above
4.2 MeV, in the absence of long-lived background, the count rates are
extrapolated to zero cosmic-ray intensity to eliminate the prompt background
and arrive at the CDG count rates. The prompt background is produced
primarily by the interactions of neutrons and protons with the spacecraft.
The delayed emission from long-lived radioactivity, present only below 4.2
MeV, is determined by fitting the energy spectrum. Their contributions are
first subtracted before the extrapolation to zero cosmic-ray flux to
determine the CDG contributions. These COMPTEL CDG flux values in the 1-30
MeV range are in good agreement with the our results reported earlier. The
COMPTEL flux in the 1-10 MeV range is about 5-10 times lower than the
pre-COMPTEL reports. The 1-30 MeV flux is consistent with power-law
extrapolations from lower and higher energies. The CDG measurements show no
evidence of a 'MeV bump' in the 1-10 MeV range.
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