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Limits for an inverse bremsstrahlung origin of the diffuse Galactic soft gamma-ray emission
Received 26 June 1998 / Accepted 31 August 1998
RXTE, GINGA, and OSSE observations have revealed an intense low-energy -ray continuum emission from the Galactic plane, which is commonly interpreted as evidence for the possible existence of a strong flux of low-energy cosmic ray electrons. In this Paper I discuss the scenario of a hadronic origin of the soft Galactic -ray continuum through inverse bremsstrahlung.
A flux of low-energy cosmic rays strong enough to produce the observed spectrum of -rays implies substantial -ray emission at a few MeV through nuclear de-excitation. It is shown that the existing limits on excess 3-7 MeV emission from the Galactic plane, in concert with the constraints from -decay -ray emission at higher energies, are in serious conflict with an inverse bremsstrahlung origin of the Galactic soft -ray emission for any physically plausible low-energy cosmic ray spectrum. While in case of energetic heavy nuclei the limits are violated by about an order of magnitude, for a large population of low-energy protons the implied -ray line flux and -decay continuum intensity are larger than the existing limits by at least a factor of 2.
Key words: acceleration of particles radiation mechanisms: non-thermal cosmic rays gamma rays: theory
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Online publication: October 21, 1998