X-ray Spectroscopy of Distant Active Galactic Nuclei

Abstract: The physical structure and behaviour of stars have been studied extensively throughout centuries.In contrast, the existence of objects now known as Active Galaxies has only been established since a couple of decades. The nucleus of such an object radiates an extraordinary amount of light across the electromagnetic spectrum, sometimes outshining the rest of the galaxy. However, since many Active Galactic Nuclei (AGNs) live in the distant universe, they are difficult to observe even with the advanced instruments of the 21st century and plenty of effort is being put into this field by astronomers wishing to understand the inner structure of these nuclei. One survey was started in 1999 by the 2002 Nobel Prize winner Riccardo Giacconi, where the Chandra telescope made several observations in the sky direction called Chandra Deep Field South. A separate pencil-beam survey of ~700 arcmin2 in this area has been performed by the telescope XMM-Newton in the ranges 2-10 keV and 5-10 keV, where the number of X-ray sources classified as AGNs is currently estimated to be 339 and 137 for each energy range, respectively. We studied two sources amongst the most brilliant in the surveys to explore their X-ray spectra and their X-ray variability and found that one is strongly absorbed in the line of sight while the other does not display any absorption. Their variability properties are also different, since the non-absorbed source displays variability behaviour similar to well known nearby AGNs in the literature.The study is limited to two intrinsically different AGNs finding that they differ not only in the spectral domain but also in the time domain.