and Cosmology

5. Active Galactic Nuclei
192
Fig. 5.16. The profile of the broad iron line is caused by
a combination of Doppler shift, relativistic beaming, and
gravitational redshift. On the left, the observed energy of
the line as a function of position on a rotating disk is indicated
by colors. Here, the energy in the right part of the
disk which is moving towards us is blueshifted, whereas the
left part of the disk emits redshifted radiation. Besides this
Doppler effect, all radiation is redshifted because the photons
must escape from the deep potential well. The smaller
the radius of the emitting region, the larger this gravitational
redshift. The line profile we would obtain from a ring-shaped
section of the disk (dashed ellipses) is plotted in the panels
on the right. The uppermost panel shows the shape of
the line we would obtain if no relativistic effects occurred
besides the non-relativistic Doppler effect. Below, the line
profile is plotted taking the relativistic Doppler effect and
beaming (see Eq. 5.31) into account. This line profile is
shifted towards smaller energies by gravitational redshift so
that, in combination, the line profile shown at the bottom
results
Fig. 5.17. The ratio of the X-ray spectrum of AGNs and a fitted
power law averaged over 53 Type 1 AGNs (left panel) and 41
Type 2 AGNs (right panel). The gray and black data points
are from two different detectors on-board the XMM-Newton
observatory. In both AGN samples, a broad relativistic iron
line is visible; in the Type 2 AGNs, an additional narrow
line component at 6.4 keV can be identified. The line strength
indicates that the average iron abundance in these sources is
about three times the Solar value