The XMM-Newton Wide-Field Survey in the COSMOS Field. IV. X-Ray Spectral Properties of Active Galactic Nuclei

We present a detailed spectral analysis of pointlike X-ray sources in the XMM-NewtonCOSMOS field. Our sample of 135 sources only includes those that have more than 100 net counts in the 0.3-10 keV energy band and have been identified through optical spectroscopy. The majority of the sources are well described by a simple power-law model with either no absorption (76%) or a significant intrinsic, absorbing column (20%). The remaining ~4% of the sources require a more complex modeling by incorporating additional components to the power law. For sourceswith more than 180 net counts (bright sample), we allowed both the photon spectral index Γ and the equivalent hydrogen column N_H to be free parameters. For fainter sources, we fix Γ to the average value and allow N_H to vary. The mean spectral index of the 82 sources in the bright sample is = 2:06 ± 0:08, with an intrinsic dispersion of ~0.24. Each of these sources has fractional errors on the value of Γ below 20%. As expected, the distribution of intrinsic absorbing column densities is markedly different between AGNs with or without broad optical emission lines. We find within our sample four type 2 QSO candidates (L_X >10^(44) ergs s^(-1), N_H >10^(22) cm^(-2)), with a spectral energy distribution well reproduced by a composite Seyfert 2 spectrum, that demonstrates the strength of the wide-field COSMOS XMM-Newton survey to detect these rare and underrepresented sources. In addition, we have identified a Compton-thick (N_H >1:5 ; 10^(24) cm^(-)2) AGN at z = 0:1248. Its X-ray spectrum is well fitted by a pure reflection model and a significant Fe Kα line at rest-frame energy of 6.4 keV.

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