ar X iv : a st ro - p h / 05 01 52 1 v 2 2 0 O ct 2 00 5 XMM - Newton Observations of High Redshift Quasars

We report on our XMM observations of the high redshift quasars BR 2237–0607 (z=4.558) and BR 0351–1034 (z=4.351). We also report on XMM observations of 19 other z> 4 objects available in the public archive of which 14 were detected. We find that the optical to X-ray spectral index αox is correlated with the luminosity density at 2500Å, but does not show a correlation with redshift, consistent with earlier results. Radio loud quasars are brighter and have flatter X-ray slopes compared to radio-quiet quasars. There is some evidence for the jet dominated sources to be intrinsically absorbed. The mean intrinsic 2-10 keV power-law slope of the 10 high redshift radio-quiet quasars in our sample for which a spectral analysis can be performed is αX=1.21±0.52 (ranging between 0.32 to 1.96), more like αX=1.19±0.10 found from the ASCA observations of low redshift Narrow-Line Seyfert 1 galaxies (NLS1s), but different from αX=0.78±0.11 found for low redshift Broad-Line Seyfert galaxies. The steep X-ray spectral index suggests high Eddington ratios L/LEdd. These observations give credence to the hypothesis of Mathur (2000) that NLS1s are low luminosity cousins of high redshift quasars. Comparison with other results from literature indicates that perhaps most luminous quasars, from low to high redshift, have similarly steep X-ray spectra suggestive of high Eddington luminosity. Subject headings: galaxies: active quasars:general quasars: individual (BR 2237–0607, BR0351–1034)