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A long look at the BALQSO LBQS 2212-1759 with XMM-Newton

A long look at the BALQSO LBQS 2212-1759 with XMM-Newton

Publication date: 04 January 2006

Authors: Clavel, J., et al.

Journal: Astronomy & Astrophysics
Volume: 446
Issue: 1
Page: 439
Year: 2006

Copyright: ESO

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 < 6 E-17 erg/cm2/s, while simultaneous UV and optical observations reveal a rather blue spectrum extending to 650 A 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 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} > 3.4 E25 cm-2. Such a large column has a Thomson optical depth to electron scattering tau > 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, > 2 E8, conflicting with the source detection below 912 A. 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 (~ 1) X-ray source is detected 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.

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