Detection of the Angular Correlation of Faint X-Ray Sources

We have analyzed a set of deep ROSAT observations with a total sky coverage of 40 deg2 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 05-10'. 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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