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Journal Articles The Astrophysical Journal Year : 2013

Deexcitation nuclear gamma-ray line emission from low-energy cosmic rays in the inner Galaxy

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Abstract

Recent observations of high ionization rates of molecular hydrogen in diffuse interstellar clouds point to a distinct low-energy cosmic-ray component. Supposing that this component is made of nuclei, two models for the origin of such particles are explored and low-energy cosmic-ray spectra are calculated which, added to the standard cosmic ray spectra, produce the observed ionization rates. The clearest evidence of the presence of such low-energy nuclei between a few MeV per nucleon and several hundred MeV per nucleon in the interstellar medium would be a detection of nuclear ϒ-ray line emission in the range E _ 0.1 - 10 MeV, which is strongly produced in their collisions with the interstellar gas and dust. Using a recent ϒ-ray cross section compilation for nuclear collisions, ϒ-ray line emission spectra are calculated alongside with the high-energy ϒ-ray emission due to π 0 decay, the latter providing normalization of the absolute fluxes by comparison with Fermi-LAT observations of the diffuse emission above E ϒ = 0.1 GeV. Our predicted fluxes of strong nuclear ϒ-ray lines from the inner Galaxy are well below the detection sensitivies of INTEGRAL, but a detection, especially of the 4.4-MeV line, seems possible with new-generation ϒ-ray telescopes based on available technology. We predict also strong ϒ-ray continuum emission in the 1-8 MeV range, which in a large part of our model space for low-energy cosmic rays exceeds considerably estimated instrument sensitivities of future telescopes.
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Dates and versions

in2p3-00762601 , version 1 (07-12-2012)

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H. Benhabiles-Mezhoud, J. Kiener, V. Tatischeff, A. W. Strong. Deexcitation nuclear gamma-ray line emission from low-energy cosmic rays in the inner Galaxy. The Astrophysical Journal, 2013, 763, pp.98. ⟨10.1088/0004-637X/763/2/98⟩. ⟨in2p3-00762601⟩
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