Lockman Hole
Lockman Hole
Fe KαIron is the end point of thermonuclear fusion in stars, and heavier elements have to be generated during supernova explosions. This makes iron the most abundant of the heavy metals with a solar abundance of NFe = 3 10-5 NH. Also, the K fluorescence yield increases with atomic number. Both of these factors account for the prominence of ~6.4 keV iron fluorescent lines in many X-ray sources.An Fe K$\alpha$ emission line at 6.4-6.7 keV is, for example, the most prominent emission feature in AGN, along with a high-energy `bump' at >20 keV, both of them probably arising from reflection of the X-rays in some thick material. Observations of many Seyfert galaxies have shown that the profile of the Fe line varies very much from source to source. In general, the reflection Fe line arises either: (a) in the inner part of the accretion disk, at about a few hundreds of gravitational radii from the black hole event horizon, where it is likely to be highly ionised and broad, and/or (b) in much more distant regions (probably at the distance of about 1 pc from the supermassive black hole) where it reveals mostly neutral Fe with a narrow line. |
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