XMM-Newton observation of the Chandra Deep Field-South: statistical treatment of faint source spectra

Abstract We present first results of the X-ray spectral analysis of 500 ksec deep survey images obtained with XMM-Newton on the Chandra Deep Field South (CDFS). Statistical distributions of spectral index and intrinsic absorption are derived for a sample containing 70 sources with a count limit of 100 (flux limit in the 2-10 keV band of 8.9×10 −16 erg cm −2 s −1 ), of which 44 sources have had redshifts identified. We observe a spatial separation between the type-1 and the type-2 AGN in diagnostics involving different X-ray parameters. Using the subsample with known z , we show that this separation between the AGN populations is a consequence of different absorption column densities. The two populations have the same average spectral index, 〈Γ〉=2±0.1. We present integrated spectra for the most distant type-2 QSO which shows strong X-ray absorption and a clear soft excess; we obtained the best fit for this object with a scattering model. We also confirm a progressive hardening for the combined integral spectra for faint objects which at first was noted by [Proceedings of the XXI Moriond Astrophysics Meeting (2001)]. Our results show a clear evolution of decrease of 〈Γ〉 with decreasing flux in the hard 2-10 keV band. However, we detect not only a regular increase in 〈Γ〉 for different subsamples of fluxes compared to Chandra results, but also a discrepancy of the values within our own data set, if we fitted in the different energy bands.