Abstract
THE weak extended X-ray source at the Galactic Centre has so far lacked a reasonable explanation. Measurements of this roughly elliptical source from the Ginga satellite revealed1 emission in the 6.7-keV line of ionized iron, indicating that the X-rays originate in an optically thin plasma. But to account for the hard X-ray spectrum, this plasma needs to be very hot — too hot, in fact, to be confined by the gravitational potential of the Galactic Centre2. We have recently shown3 that the morphology of the emitting region changes at energies above 11 keV: the source becomes extended in the galactic plane, resembling the distribution of the molecular gas clouds in this region. Here we report the detection of a pronounced absorption feature in the emission spectrum in the energy range 8–11 keV. This result, combined with the changing spatial distribution, suggests that the high-energy emissions arise from the scattering of X-rays from the nearby compact sources by the dense molecular clouds. As no comparable absorption feature is seen at lower energies, the softer X-ray emissions may still be understood in terms of thermal emission from a plasma, but the required temperature is no longer unreasonably high.
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Markevitch, Sunyaev, R. & Pavlinsky, M. Two sources of diffuse X-ray emission from the Galactic Centre. Nature 364, 40–42 (1993). https://doi.org/10.1038/364040a0
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DOI: https://doi.org/10.1038/364040a0
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