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

¹ Research & Scientific Support Department, ESTEC, SCI-SA, Postbus 299 2200 AG – Noordwijk, The Netherlands e-mail: Jean.Clavel@esa.int
² XMM-Newton Science Operations Centre, ESAC, Apartado 50727, 28080 Madrid, Spain e-mail: [nscharte;ltomas]@xmm.vilspa.esa.es

Received: 6 September 2004
Accepted: 9 September 2005

Abstract

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, , while simultaneous UV and optical observations reveal a rather blue spectrum extending to 650 Åin the source rest frame. These results are used to set a tight upper-limit on its optical to X-ray spectral index . 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 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 . Such a large column has a Thomson optical depth to electron scattering , 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, , 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 completely covers the compact X-ray source but only partially the more extended source of ultraviolet photons. An extended () X-ray source is detected to the south-east of the QSO. Given its thermal spectrum and temperature (), it is probably a foreground () cluster of galaxies.