Abstract
We present a detailed characterization of the X-ray spectral properties of 761 type 1 AGN, selected from a cross-correlation of the SDSS DR5 quasar catalogue and the incremental version of the second XMM-Newton serendipitous X-ray source catalogue 2XMMi-DR2. The X-ray spectrum of each source is fit with models based on a simple power law to which additional cold absorption and/or soft excess features are added if an F-test at 99% significance requires them. The distribution of best-fitting photon indices, Gamma, is fit with a Gaussian with mean <gamma> = 1.99 +/- 0.01 and dispersion sigma = 0.30 +/- 0.01, however this does not provide a good representation of the distribution due to sources with very flat or steep gamma values. A highly significant trend for decreasing gamma values with increasing 2-10 keV luminosity, L_X, is seen but only a weak trend with redshift is found. Intrinsic cold absorption is detected in ~4% of the sample and soft excess emission is detected in ~8%. These values are lower limits due to the detectability being limited by the quality of the spectra and we suggest the intrinsic values may be as high as ~25% and ~80% respectively. The levels of rest-frame absorption are higher than expected for type 1 objects (N_H = 10^21-10^23 cm^-2) and the fraction of absorbed sources and the N_H values are not seen to vary with L_X or z. The average blackbody temperature used to model the soft excesses is <kT> = 0.17 +/- 0.09 keV. This temperature is found to correlate with L_X but not the blackbody luminosity or the black hole mass which do correlate with each other. A strong correlation is found between the luminosities in the blackbody and power law components suggesting that a similar fraction is re-processed from the blackbody to the power law component for the entire luminosity range of objects. . . [Abridged]
Highlights
It is widely accepted that Active Galactic Nuclei (AGN) are accreting supermassive (M > 106M⊙) black holes (SMBH) residing at the centre of galaxies (Lynden-Bell 1969)
Both fractions fall with decreasing counts. As this could be due to our reducing sensitivity to these extra components we have performed simulations of the detectability of typical values of these as a function of counts (Scott et al in prep). We find that these simulations reproduce almost exactly the behaviour observed in Figure 4, suggesting that the level of required soft excess and absorption within the overall type 1 AGN population could be as high as the 80% and 25% found in the highest count range
The main conclusions from this analysis of the largest sample of AGN X-ray spectra are summarized below: (i) When the distribution of best-fitting power law slopes is modelled with a single Gaussian as done in previous works, the best-fitting values are found to be Γ = 1.99 ± 0.01 with an dispersion of σ Γ = 0.30 ± 0.01
Summary
It is widely accepted that Active Galactic Nuclei (AGN) are accreting supermassive (M > 106M⊙) black holes (SMBH) residing at the centre of galaxies (Lynden-Bell 1969) They have bolometric luminosities which can be as high as ∼ 1048. The earliest observations of AGN revealed that their Xray spectra were remarkably similar, and could be described by a simple power law (Mushotzky et al 1980). This primary X-ray emission is believed to be due to inverse Compton scattering of low energy UV photons from the accretion disc. It has been suggested that the reflection component could be intrinsically weaker in high luminosity quasars since the inner accretion disc is more likely to become ionized, reducing the amount of neutral matter remaining, which is required to create a reflection feature (e.g. Mushotzky et al 1993)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
