Observations of shadows in the diffuse X-ray radiation at an energy of 1/4 keV have essentially changed our understanding of its origin. The image shows an X-ray intensity image in the constellation Draco. The contour lines show the IRAS 100 µm emission. Since the Draco Nebula is more than 1,000 light years away from the Sun and more than 650 light years above the Galactic plane this shadow suggests X-ray radiation from a halo at least partially surrounding our Milky Way.
Snowden, S. L., U. Mebold, W. Hirth, U. Herbstmeier, and J. H. M. Schmitt,
Rosat detection of an x-ray shadow in the 1/4-kev diffuse background in the
draco nebula, Science 252, 1529-1532 (1991)
see also: LHEA Soft X-ray Diffuse Background Home Page
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