However, there are a few arguments allowing also different explanations for the radiation from molecular clouds in the vicinity of the Galactic Center. Fluorescence is a natural consequence of absorption. Compton scattered radiation plus a fluorescence line should be accompanied by an absorption edge, in this case by the iron K-edge at 7.1 keV. Given the iron K fluorescence yield, about three times more photons must be absorbed than reradiated in the Ka line. However, the filamentary structures within the radio arc do not exhibit such an edge . Furthermore despite their different distances from Sgr A*, the filaments have more or less comparable surface brightnesses that is not necessarily a consequence of the continously decreasing luminosity of Sgr A*. The spectra of the reflection nebulae are reasonably fit by bremsstrahlung and lines from neutral iron. Those spectra could also be created by the impact of electrons (or protons at higher energies) as in laboratory X-ray tubes. There are sufficient hints on the existence of those electrons: one of the great mysteries is the Galactic ridge X-ray emission [5,25,29], which has a scale height of «100pc and is greatly enhanced toward the Galactic Center. The overall spectrum of the ridge emission suggests a characteristic thermal temperature of 7-10 keV. Diffuse hot gas with such temperatures would escape fast into the galactic halo, demanding a very efficient heating source, which is not found in the Galactic Center. As an alternative, a nonthermal origin of the galactic X-ray background has been proposed, e.g., electrons that could be also responsible for the 6.4keV fluorescence line-similar to an ordinary X-ray tube in laboratory.
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