  This paper presents the clustering properties of hard (2-8 keV) X-ray
selected sources detected in a wide field ($\approx \rm 2 deg^{2}$) shallow
[$f_X(\rm 2-8 keV)\approx 10^{-14}\rm erg cm^{-2} s^{-1}$] and contiguous
XMM-{\it Newton} survey. We perform an angular correlation function analysis
using a total of 171 sources to the above flux limit. We detect a $\sim
4\sigma$ correlation signal out to 300 arcsec with $w(\theta < 300^{''})\simeq
0.13 \pm 0.03$. Modeling the two point correlation function as a power law of
the form $w(\theta)=(\theta_{\circ}/\theta)^{\gamma-1}$ we find:
$\theta_{\circ}=48.9^{+15.8}_{-24.5}$ arcsec and $\gamma=2.2\pm {0.30}$. Fixing
the correlation function slope to $\gamma=1.8$ we obtain
$\theta_{\circ}=22.2^{+9.4}_{-8.6}$ arcsec. Using Limber's intergral equation
and a variety of possible luminosity functions of the hard X-ray population, we
find a relatively large correlation length, ranging from $r_{\circ}\sim 9$ to
19 $h^{-1}$ Mpc (for $\gamma=1.8$ and the {\em concordance} cosmological
model), with this range reflecting also different evolutionary models for the
source luminosities and clustering characteristics. The relatively large
correlation length is comparable to that of extremely red objects and luminous
radio sources.
