Very long ( 172 ks effective exposure time ) observations of the BALQSO LBQS~2212-1759 with XMM-Newton yield a stringent upper-limit on its 0.2–10 keV ( rest- frame 0.64–32.2 keV ) flux , { F _ { 0.64 - 32.2 } \leq 6 \times 10 ^ { -17 } ~ { } erg cm ^ { -2 } s ^ { -1 } } , while simultaneous UV and optical observations reveal a rather blue spectrum extending to 650 Å in the source rest frame .
These results are used to set a tight upper-limit on its optical to X-ray spectral index { \alpha _ { ox } \leq - 2.56 } .
Given the HI-BAL nature of LBQS 212-1759 , its X-ray weakness is most likely due to intrinsic absorption .
If this is the case , and assuming that the intrinsic { \alpha _ { ox } } of LBQS 2212-1759 is -1.63 – a value appropriate for a radio-quiet quasar of this luminosity – one can set a lower limit on the X-ray absorbing column { N _ { H } \geq 3.4 10 ^ { 25 } cm ^ { -2 } } .
Such a large column has a Thomson optical depth to electron scattering { \tau _ { Th } \geq 23 } , sufficient to extinguish the optical and UV emission .
The problem only gets worse if the gas is neutral since the opacity in the Lyman continuum becomes extremely large , { \tau _ { Ly } \geq 2 \times 10 ^ { 8 } } , conflicting with the source detection below 912 Å .
This apparent contradiction probably means that our lines-of-sight to the X-ray and to the UV emitting regions are different , such that the gas covers completely the compact X-ray source but only partially the more extended source of ultraviolet photons .
An extended ( \simeq 1 \arcmin ) X-ray source is detected \sim 2 \arcmin to the south-east of the QSO .
Given its thermal spectrum and temperature ( { 1.5 \leq T \leq 3.0 keV } ) , it is probably a foreground ( 0.29 \leq z \leq 0.46 ) cluster of galaxies .