The EXOSAT High Galactic Latitude Survey /

The authors have performed a survey of ≡570 square degrees of high galactic latitude sky using a large number of EXOSAT X-ray images. 130 serendipitous sources were detected and ≡60% of them have been identified with catalogued objects. The large majority of the remaining sources have faint optical counterparts on POSS or ESO plates and are expected to be extragalactic. The comparison of the results with those of the Einstein Medium Sensitivity Survey and an analysis of the correlation between the spatial distribution of EXOSAT serendipitous sources and the amount of galactic hydrogen column density indicate that the average spectral index of extragalactic X-ray sources is steeper than the canonical AGN slope.