An X-ray view of the INTEGRAL/IBIS blazars
  Aim of this work is a broad-band study with INTEGRAL, Swift and XMM-Newton
satellites of a sample of 9 blazars (7 FSRQ and 2 BL Lac) with redshift up to
about 4. The spectral analysis has shown clear evidence of a flattening of the
continuum towards the low energies ($E<3$ keV observer frame). This behaviour
is well reproduced both with an absorbed power-law model
($N_H\sim10^{20}$-$10^{23}$ cm$^{-2}$ in the rest-frame of the sources) or a
broken power-law continuum model (with an energy break below 3 keV in the
observer-frame). No Compton reflection features, Fe $K\alpha$ line and hump at
high energies, have been detected, with the exception of the source IGR
J22517+2218 that shows the presence of a weak iron line. In this work we also
investigate a possible correlation between the absorption column density $N_H$
and the red-shift. We confirm the existence of a $N_H$-z trend, with the higher
absorption at z$>$2 for a larger sample compared to previous results. The
distribution of the $N_H$ and the photon index $\Gamma$ is also presented. The
hard X-ray data allow us to detect highly absorbed sources (with
$N_H\ge10^{23}$cm$^{-2}$ in rest-frame of the source) characterized by photon
index distribution peaked at harder values ($\Gamma\sim1.4$) with respect to
that obtained with XMM data only ($\Gamma\sim2$).
