Long observations of the BALQSO LBQS 2212-1759 with XMM-Newton

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, F0.64-32.2 <= 6 x 10(-17) erg cm(-2) s(-1), while simultaneous UV and optical observations reveal a rather blue spectrum extending to 650 angstrom 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) <= -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 aox 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 >= 3.4 x 10(25) cm(-2). Such a large column has a Thomson optical depth to electron scattering tau(Th) >= 23, sufficient to extinguish the optical and UV emission. The contradiction becomes even more acute if the gas is neutral since the opacity in the Lyman continuum becomes extremely large, tau(Ly) = 2 x 10(8), conflicting with the source detection below 912 angstrom. 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 completely covers the compact X-ray source but only partially the more extended source of ultraviolet photons. An extended (similar or equal to 1') X-ray source is detected similar to 2' to the south-east of the QSO. Given its thermal spectrum and temperature (1.5 <= T <= 3.0 keV), it is probably a foreground (0.29 <= z <= 0.46) cluster of galaxies.