Abstract
We present the results of a ROSAT XRT/PSPC observation of a field near the North Galactic Pole containing the interacting galaxy pair NGC 4725/4747. A tidal H I plume emanating from NGC 4747 and also the extended HI disc in NGC 4725 represent foreground screens which will, in principle, cast shadows on any extra-galactic component of the soft X-ray background. The failure to detect such shadowing in the ROSAT observation leads to a 95 per cent upper limit on the intensity of the unresolved extragalactic background of 26.5 keV cm −2 s −1 sr −1 keV −1 at 0.25 keV, after excluding discrete sources brighter than 1.7×10 −14 erg cm −2 s −1 in the 0.5-2 keV band
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