The large-scale diffuse X-ray emission surrounding quasars: an   investigation using the scaling-index method
  The large-scale (~ 20') diffuse x-ray background surrounding a sample of quasars observed during ROSAT PSPC pointed observations is studied using a new source-detection algorithm, the scaling-index method. This algorithm, which can identify individual photons as belonging to a source or background, is useful for detecting faint, extended sources in noisy fields. Using this method, we find that, contrary to conclusions drawn by others, there is scant evidence for preferential enhancement of x-ray backgrounds surrounding radio-loud quasars by foreground x-ray emitting clusters of galaxies. Rather, all fluctuations in these backgrounds can be explained by varying levels of emission from a galactic thermal plasma of temperature T ~ 0.14 keV. No difference is observed between the diffuse x-ray backgrounds of radio-loud and radio-quiet quasars. 
K. A. Williams, W. Brinkmann and G. Wiedenmann (MPE Garching)