University of Leicester
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Spectral Properties of AGN in 2XMMi

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posted on 2013-01-10, 13:53 authored by Amy Elizabeth Scott
Studying the emission of Active Galactic Nuclei (AGN), particularly in the X-ray band can offer considerable insights into the accretion process. This is important as AGN activity has a strong effect on the evolution of their host galaxies. This thesis reports studies of a large sample of type 1 AGN, created by cross-correlating the optical SDSS DR5 quasar catalogue and the catalogue of serendipitous X-ray source detections, 2XMMi. A sample of 761 sources with X-ray spectra of sufficient quality for spectral modelling was obtained. The typical spectral shape of the sources is a power law of ‹Γ› = 1.99 ± 0.01 with an intrinsic dispersion of σ‹Γ› = 0.30 ± 0.01. However, ~ 3% were found to have intrinsically flat or steep Γ slopes. Significant trends between Γ and LX and Γ and Eddington ratio were found. The radio loudness of the sources was also determined and the RLQ show higher LX values and flatter Γ values than RQQ, suggesting an additional X-ray component is present. Intrinsic cold absorption was found in ~ 4% of sources with NH ~ 1021 − 1023 cm−2, despite being unexpected in optically classified type 1 AGN. A soft excess was found in ~ 8% of sources with an average blackbody temperature of ‹kT› = 0.17 ± 0.09 keV. This temperature correlates with LX and a strong correlation is found between the luminosities in the blackbody and power-law components. The detectability of these additional components is limited by the quality of the spectra. By simulating spectra with typical spectral shapes, the intrinsic percentage of the sample with a soft excess was found to be 75 ± 23%. The sample is also cross-correlated with archival multiwavelength catalogues and spectral energy distributions are created for each object. The infrared to ultraviolet region is found to be similar between sources regardless of their radio loudness, and the SEDs of low luminosity, low accretion rate sources tend to be flatter, with the optical/UV disc emission becoming more prominent with increases in these parameters.



Stewart, Gordon; Watson, Michael

Date of award


Awarding institution

University of Leicester

Qualification level

  • Doctoral

Qualification name

  • PhD



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