Properties of the integrated spectrum of active galactic nuclei
b'The aim of this thesis is to characterize the properties of the integrated spectrum of active galactic nuclei(AGNs), such as the ubiquity of the Fe K\\u03b1 emission in AGNs, the dependence of the spectral parameters(e.g. the power law photon index and the Fe K\\u03b1 equivalent width etc.) on the X-ray luminosity and redshift, and mean properties (including the line profile) of the Fe K\\u03b1 line which can be addressed via stacking in the source rest-frame.\\nI selected 2646 point sources observed with XMM-Newton at high galactic latitude (|BII| > 25 degrees) and with the sum of EPIC-PN and EPIC-MOS 0.2\\u201312 keV counts greater than\\n1000. Redshifts were obtained for 919 sources from the Nasa\\u2019s Extragalactic Database. In order to prepare a clean sample, I retained only reliable sources (those for which the detection and the spectral products do not show obvious problems). I also excluded sources classified as HII\\nregions, groups/clusters, star-forming/starburst galaxies. The final sample consists of 507 AGNs.\\nTo examine the ubiquity of the Fe K\\u03b1 emission in AGNs and the dependence of the spectral parameters on the X-ray luminosity and redshift, I employed the observed-frame stacking technique, in which individual source spectra were summed in the observed-frame to compute the integrated spectra in different redshift and luminosity bins over the range 0 < z < 5. Detailed analysis of these spectra used appropriately normalized background spectra and exposure time weighted response and ancillary files. I find that the narrow Fe K\\u03b1 line at 6.4 keV is significantly detected up to z = 1. The line equivalent width decreases with increasing the X-ray luminosity in the 2\\u201310 keV band (\\u201cIwasawa-Taniguchi effect\\u201d). The anticorrelation is characterized by the relation log(EW_Fe) = (1.66 \\xb1 0.09) + (\\u22120.43 \\xb1 0.07) log(LX,44), where EW_Fe is the rest-frame equivalent width of the neutral Fe K\\u03b1 line in eV and LX,44 is the 2\\u201310 keV X-ray luminosity in units of 10^44 erg/s. The equivalent width is nearly independent of redshift up to z \\u223c 0.8 with\\nan average value of 101 \\xb1 40 (rms dispersion) eV in the luminosity range 43.5 \\u2264 log LX \\u2264 44.5. This analysis also confirms the hardening of the spectral indices at low luminosities, implying a dependence of obscuration on luminosity.\\nTo derive the mean properties of the Fe K\\u03b1 line in the source rest-frame, I refined the final sample of 507 AGNs and selected 248 AGNs with the EPIC-PN net 2\\u201310 keV rest-frame counts \\u2265200 and power law photon indices in the range 1.5\\u20132.2. I computed the integrated spectrum of these 248 AGNs in the source rest-frame using two different rest-frame stacking procedures. I carried out a detailed spectral analysis of these integrated spectra using various models comprising simple/complex continuum and Fe K\\u03b1 line components. I find that the average Fe K\\u03b1 line profile in our sample is best represented by a combination of a narrow and a broad line. The equivalent widths of the narrow and broad components are \\u223c30 eV and \\u223c100 eV, respectively. The broad line parameters such as its shape, equivalent width and its detection significance in the integrated spectrum of the 248 AGNs are observed to be very sensitive to the assumed continuum and adopted stacking method. However, despite having a well-defined sample with reasonable statistics (net counts \\u223c 198000) in the integrated spectrum, I do not detect a clear extended red-wing, and the measured equivalent width of the broad feature is always lower than 170 eV, implying that most black holes are not maximally rotating.'