...)

An additional source, XID = 62 from Giacconi et al. (2002), which would fit these selection criteria has been excluded since the optical spectroscopy reveals its BAL-QSO nature.

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... III]  $\lambda 5007$

Emission line fluxes for 7 of the sources are also shown in a paper by Nagao et al. that was submitted to publication after the submission of our paper - see arXiv:astro-ph/0508652.

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... survey

The optical spectra are publicly available at: http://www.bo.astro.it/~hellas/sample.html

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