8,405 research outputs found
Modelling cosmic rays and gamma rays in the Galaxy
An extensive program for the calculation of galactic cosmic-ray propagation
has been developed. This is a continuation of the work described in Strong &
Youssefi (1995). The main motivation for developing this code is the prediction
of diffuse Galactic gamma rays for comparison with data from the CGRO
instruments EGRET, COMPTEL, and OSSE. The basic spatial propagation mechanisms
are (momentum-dependent) diffusion, convection, while in momentum space energy
loss and diffusive reacceleration are treated. Primary and secondary nucleons,
primary and secondary electrons, and secondary positrons are included.
Fragmentation and energy losses are computed using realistic distributions for
the interstellar gas and radiation fields.
This study indicates that it is possible to construct a model satisfying a
wide range of observational constraints and provides a basis for future
developments.Comment: 5 pages including 7 figures, latex, aipproc.sty, aipproc.cls,
epsfig.sty. To be published in Proc. 4th Compton Symp., 1997 (27-30 April,
Williamsburg, Virginia). Details can be found at
http://www.gamma.mpe-garching.mpg.de/~aws/aws.htm
A New Determination Of The Diffuse Galactic and Extragalactic Gamma-Ray Emission
The GALPROP model for cosmic-ray propagation is able to make explicit
predictions for the distribution of galactic diffuse gamma-rays. We compare
different propagation models with gamma-ray spectra measured by EGRET for
various regions of the sky. This allows sensitive tests of alternative
explanations for the apparent excess emission observed at GeV gamma-rays. We
find that a population of hard-spectrum gamma-ray sources cannot be solely
responsible for the excess since it also appears at high latitudes; on the
other hand a hard cosmic-ray electron spectrum cannot explain the gamma-ray
excess in the inner Galaxy. By normalizing the cosmic ray spectra within
reasonable bounds under preservation of their shape we are able to obtain our
best prediction of the Galactic component of diffuse gamma rays, and show that
away from the Galactic plane it gives an accurate prediction of the observed
gamma-ray intensities. On this basis we reevaluate the extragalactic gamma-ray
background. We find that for some energies previous work underestimated the
Galactic contribution and hence overestimated the background. The new EGRB
spectrum shows a positive curvature similar to that expected for models of the
extragalactic gamma-ray emission based on contributions from unresolved
blazars.Comment: 6 pages, 3 figures, 1 tabl
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