We present the analysis and the results of a 20 ks XMM–Newton observation of the extremely X-ray loud ( L _ { X } \approx 5 \times 10 ^ { 47 } erg s ^ { -1 } ) flat–spectrum radio quasar RBS 315 at a redshift of 2.69 .
This EPIC observation has allowed us to strongly constrain the slope of the continuum ( \Gamma = 1.23 \pm 0.01 ) as well as to discover the presence of a sharp drop below \approx 2 keV in its spectrum .
Such a flat photon index and the huge luminosity suggest that the X-ray emission is due to the low energy tail of the Comptonized spectrum , produced from plasma in a relativistic jet oriented close to our line of sight .
Even though the hypothesis of a break in the continuum can not be completely discarded as an explanation of the soft X-ray cutoff , the presence of intrinsic absorption appears more plausible .
Spectral fits with cold ( N _ { H } ^ { z } = 1.62 ^ { +0.09 } _ { -0.09 } \times 10 ^ { 22 } cm ^ { -2 } ) and lukewarm ( N _ { H } ^ { z } = 2.2 ^ { +0.9 } _ { -0.3 } \times 10 ^ { 22 } cm ^ { -2 } ; \xi = 15 ^ { +38 } _ { -12 } erg cm ^ { -2 } s ^ { -1 } ) absorbers are statistically indistinguishable .
Remarkably , our results are very similar to those reported so far for other absorbed high- z Blazars observed by XMM–Newton .
The existence of this “ homogeneous ” class of jet-dominated superluminous obscured QSOs at high z therefore could be important in the context of the formation and cosmological evolution of radio-loud objects .