THE DIFFUSE SOFT-X-RAY BACKGROUND AS SEEN WITH THE EINSTEIN-OBSERVATORY

We present a systematic survey of the diffuse soft X-ray background as seen directly with the Einstein Observatory. Using 1633 selected 1-degrees x 1-degrees fields of view obtained by the Imaging Proportional Counter (IPC) to provide almost-equal-to 5% sky coverage, with some bias toward the Galactic plane, we are able to spatially resolve the background in the 0.16-3.5 keV spectral region on this angular scale. The moderate energy resolution of the IPC also enables us to characterize and produce maps of the background at different energies within the Einstein passband. We confirm that the Galactic ridge is not present at energies below 0.33 keV and demonstrate that the appearance of the ridge above this energy is not due to hard Galactic sources with a flux above 10(-13) ergs cm-2 s-1. We have identified a southern Galactic region, with l between 80-degrees and 180-degrees and b less than -5-degrees, where the mean background intensity has the lowest value and is homogeneous within better than 9%; the background in this region likely represents an isotropic component with mean intensity, in the (9.16-2.7 keV energy range) of almost-equal-to 19 keV cm-2 keV-1 sr-1, approximately 2.5 times more than the value extrapolated from higher energy measurements. We discuss the implications of our results for Galactic structure and for the nature of the extragalactic X-ray background.