  Although absorbed quasars are extremely important for our understanding of
the energetics of the Universe, the main physical parameters of their central
engines are still poorly known. In this work we present and study a complete
sample of 14 quasars (QSOs) that are absorbed in the X-rays (column density
NH>4x10^21 cm-2 and X-ray luminosity L(2-10 keV)>10^44 ergs/s; XQSO2) belonging
to the XMM-Newton Bright Serendipitous Survey (XBS). From the analysis of their
ultraviolet-to-mid-infrared spectral energy distribution we can separate the
nuclear emission from the host galaxy contribution, obtaining a measurement of
the fundamental nuclear parameters, like the mass of the central supermassive
black hole and the value of Eddington ratio, lambda_Edd. Comparing the
properties of XQSO2s with those previously obtained for the X-ray unabsorbed
QSOs in the XBS, we do not find any evidence that the two samples are drawn
from different populations. In particular, the two samples span the same range
in Eddington ratios, up to lambda_Edd=0.5; this implies that our XQSO2s
populate the "forbidden region" in the so-called "effective Eddington limit
paradigm". A combination of low grain abundance, presence of stars inwards of
the absorber, and/or anisotropy of the disk emission, can explain this result.
