ROSAT HRI observations of seven high redshift quasars
  We present ROSAT HRI observations of six quasars with redshifts >3.4: PKS 0335-122, S4 0620+389, B1422+231, PKS 2215+02, Q 2239-386 and PC 2331+0216. We include the observation of the radio-quiet quasar BG 57 9, whose redshift has recently been revised to z = 0.965. S4 0620+389, B1422+231, PKS 2215+02 and BG 57 9 are detected in the ROSAT energy band (0.1-2.4 keV). 2 sigma upper limits are given for the remaining objects. All X-ray sources are point like to the limit of the HRI point spread function. We report marginal evidence for X-ray variability in S4 0620+389 on timescales of several hours (rest frame). No significant X-ray variability is found in the gravitationally lensed quasar B1422+231 on rest frame timescales of hours and months. We present the spectral energy distributions for six of the high redshift quasars and compare them to the mean distribution of low redshift quasars. 
J. Siebert and W. Brinkmann (Max-Planck-Institut f. extraterrestrische   Physik, MPE)