DIFFUSE-X-RAY EMISSION AROUND HIGH-REDSHIFT, RADIO-LOUD QSOS

We announce the detection of correlations on angular scales of greater than or similar to 10' between optically bright, high-redshift, radio -loud QSOs with diffuse X-ray emission seen by ROSAT in the All-Sky Su rvey. These correlations reach significance levels of up to 99.8%. A c omparison of the results with a sample of control fields, bootstrappin g analyses, and Kolmogorov-Smirnov tests provide unambiguous support f or the statistical significance of the correlations found. We argue th at the detected enhanced diffuse X-ray emission is in the foreground o f the QSOs, and that it is probably due to galaxy clusters which magni fy the QSOs by their gravitational lensing effect, thereby giving rise to a magnification bias in the background source sample. A comparison of the results presented below with correlations previously found bet ween the same QSO sample and either Lick or IRAS galaxies provides fur ther evidence for this interpretation, and identifies positions in the sky where weak gravitational lensing may be detected by searching for coherent distortions of background galaxy images.