We present a spectroscopic study of 41 hard X-ray sources detected serendipitously with high significance ( > 5 \sigma in the 2-10 keV band ) in seven EPIC performance/verification phase observations .
The large collecting area of EPIC allows us to explore the spectral properties of these faint hard X-ray sources with 2 < F _ { 2 - 10 } < 80 \times 10 ^ { -14 } erg cm ^ { -2 } s ^ { -1 } even though the length of the exposures are modest ( \sim 20 ks ) .
Optical identifications are available for 21 sources of our sample .
Using a simple power law plus Galactic absorption model we find an average value of the photon index \Gamma \sim 1.6-1.7 , broadly consistent with recent measurements made at similar fluxes with ASCA and with Chandra stacked spectral analyses .
We find that 31 out of 41 sources are well fitted by this simple model and only eight sources require absorption in excess of the Galactic value .
Interestingly enough , one third of these absorbed sources are broad line objects , though with moderate column densities .
Two sources in the sample are X-ray bright optically quiet galaxies and show flat X-ray spectra .
Comparing our observational results with those expected from standard synthesis models of the cosmic X-ray background ( CXB ) we find a fraction of unabsorbed to absorbed sources larger than predicted by theoretical models at our completeness limit of F _ { 2 - 10 } \sim 5 \times 10 ^ { -14 } erg cm ^ { -2 } s ^ { -1 } .
The results presented here illustrate well how wide-angle surveys performed with EPIC on board XMM-Newton allow population studies of interesting and unusual sources to be made as well as enabling constraints to be placed on some input parameters for synthesis models of the CXB .