We have analyzed a set of deep ROSAT observations with a total sky coverage of 40 deg~2 to search for clustering of faint X-ray sources. Using the resulting catalog of discrete X-ray sources, we detect, for the first time in the X-ray band, a positive correlation on angular scales of 0.5′-10′. When corrected for a bias due to limited spatial resolution, which amplifies the correlation, the observed angular correlation function agrees well with that expected from the spatial correlation of optically selected quasars provided that they comprise an appreciable fraction (≥50%) of detected X-ray sources.
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