In the ROSAT Survey, the entire sky was mapped and sources were visible a hundred times fainter than in any previous survey. Altogether, 150,000 X-ray sources were discovered with ROSAT, twenty-five times more than with all previous X-ray satellites together. In the survey with its unlimited field of view, regions of diffuse X-ray emission, for instance from the supernova remnants and clusters of galaxies, were reproduced and spectroscopally analyzed for the first time. The ROSAT All-Sky Survey Bright Source Catalogue (RASS-BSC) was derived from the all-sky survey containing 18,811 sources with a limiting ROSAT PSPC count rate of 0.05 counts/s.
Figure 1: The 18,811 sources in this map are catalogued, with a limiting ROSAT PSPC count rate of 0.05 cts/s in the 0.1-2.4 keV energy band. The sources have a detection likelihood of at least 15 and contain at least 15 source photons. At a brightness limit of 0.1 cts/s (8,547 sources) the catalogue represents a sky coverage of 92%. The typical positional accuracy is 30 arcsec.
Figure 2: ROSAT sky map for the energy range 0.5-0.9 keV (3/4 keV band) in zero-centered, north-oriented galactic coordinates with an Aitoff equal-area projection. The galactic plane is represented by the horizontal line. The X-rays are emitted mainly by some million-degree gases such as stellar coronae, supernova remnants, superbubbles, and the hot plasma of the galactic nucleus. Aside from this, one can recognize a weak isotropic extragalactic radiation from the superposition of unresolved active galaxies and clusters of galaxies.
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