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|Title:||Searching for highly obscured AGNs in the XMM-Newton serendipitous source catalog|
Watson, M. G.
Rosen, S. R.
Page, K. L.
Stewart, G. C.
Pye, John Patrick
|Publisher:||EDP Sciences for European Southern Observatory (ESO)|
|Citation:||Astronomy & Astrophysics, 2014, 569, A71|
|Abstract:||The majority of active galactic nuclei (AGNs) are obscured by large amounts of absorbing material that makes them invisible at many wavelengths. X-rays, given their penetrating power, provide the most secure way for finding these AGNs. The XMM-Newton serendipitous source catalog, of which 3XMM-DR4 is the latest version, is the largest catalog of X-ray sources ever produced; it contains about half a million detections. These sources are mostly AGNs. We have derived X-ray spectral fits for very many 3XMM-DR4 sources (≳114 000 observations, corresponding to ~77 000 unique sources), which contain more than 50 source photons per detector. Here, we use a subsample of ≃1000 AGNs in the footprint of the SDSS area (covering 120 deg2) with available spectroscopic redshifts. We searched for highly obscured AGNs by applying an automated selection technique based on X-ray spectral analysis that is capable of efficiently selecting AGNs. The selection is based on the presence of either a) flat rest-frame spectra from a simple power-law fit; b) flat observed spectra from an absorbed power-law fit; c) an absorption turnover, indicative of a high rest-frame column density; or d) the presence of an Fe Kα line with a large equivalent width (>500 eV). We found 81 highly obscured candidate sources. Subsequent detailed manual spectral fits revealed that 28 of them are heavily absorbed by column densities higher than 10[Superscript: 23] cm[Superscript: -2]. Of these 28 AGNs, 15 are candidate Compton-thick AGNs on the basis of either a high column density, consistent within the 90% confidence level with NH> 10[Superscript: 24] cm[Superscript: -2], or a large equivalent width (>500 eV) of the Fe Kα line. Another six are associated with near-Compton-thick AGNs with column densities of ~ 5 × 10[Superscript: 23] cm[Superscript: -2]. A combination of selection criteria a) and c) for low-quality spectra, and a) and d) for medium- to high-quality spectra, pinpoint highly absorbed AGNs with an efficiency of 80%.|
|Rights:||Copyright © 2014 ESO. Reproduced with permission from Astronomy & Astrophysics, © ESO.|
|Appears in Collections:||Published Articles, Dept. of Physics and Astronomy|
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