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

H. Benhabiles-Mezhoud 1 J. Kiener 2 V. Tatischeff 1 A. W. Strong 3
1 CSNSM AN
CSNSM - Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse, CSNSM - Centre de Sciences Nucléaires et de Sciences de la Matière
2 CSNSM AS
CSNSM - Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse
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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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. Astronomy and Astrophysics - A&A, EDP Sciences, 2012, 551, pp.A128. ⟨10.1051/0004-6361/201220870⟩. ⟨in2p3-00762601⟩

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