We present XMM-Newton X-ray spectra and optical photometry of four high redshift ( z = 2.96 - -3.77 ) quasars , [ HB89 ] 0438 - 436 , [ HB89 ] 2000 - 330 , [ SP89 ] 1107+487 and RX J122135.6+280613 ; of these four objects the former two are radio-loud , the latter two radio-quiet .
Model fits require only a power law with Galactic absorption in each case ; additional intrinsic absorption is also needed for [ HB89 ] 0438 - 436 and RX J122135.6+280613 .
The spectra are hard ( \Gamma \sim 1.7 for [ HB89 ] 0438 - 436 , [ HB89 ] 2000 - 330 and \sim 1.4 for RX J122135.6+280613 ) with the exception of [ SP89 ] 1107+487 which is softer ( \Gamma \sim 2.0 ) ; the combined Galactic and intrinsic absorption of lower energy X-rays in the latter source is much less significant than in the other three .
The two intrinsically unabsorbed sources have greater optical fluxes relative to the X-ray contributions at the observed energies .
While there is no need to include reflection or iron line components in the models , our derived upper limits ( 99 % confidence ) on these parameters are not stringent ; the absence of these features , if confirmed , may be explained in terms of the high power law contribution and/or a potentially lower albedo due to the low disc temperature .
However , we note that the power-law spectrum can be produced via mechanisms other than the Comptonization of accretion disc emission by a corona ; given that all four of these quasars are radio sources at some level we should also consider the possibility that the X-ray emission originates , at least partially , in a jet .