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http://hdl.handle.net/20.500.12386/26877
Titolo: | The NuSTAR Serendipitous Survey: Hunting for the Most Extreme Obscured AGN at >10 keV | Autori: | Lansbury, G. B. Alexander, D. M. Aird, J. Gandhi, P. Stern, D. Koss, M. Lamperti, I. Ajello, M. Annuar, A. Assef, R. J. Ballantyne, D. R. Baloković, M. Bauer, F. E. Brandt, W. N. Brightman, M. Chen, C. -T. J. Civano, F. COMASTRI, Andrea Del Moro, A. Fuentes, C. Harrison, F. A. MARCHESI, STEFANO Masini, A. Mullaney, J. R. Ricci, C. Saez, C. Tomsick, J. A. Treister, E. Walton, D. J. Zappacosta, L. |
Data pubblicazione: | 2017 | Rivista: | THE ASTROPHYSICAL JOURNAL | Numero: | 846 | Fascicolo: | 1 | Da pagina:: | 20 | Abstract: | We identify sources with extremely hard X-ray spectra (I.e., with photon indices of {{Γ }}≲ 0.6) in the 13 deg<SUP>2</SUP> NuSTAR serendipitous survey, to search for the most highly obscured active galactic nuclei (AGNs) detected at > 10 {keV}. Eight extreme NuSTAR sources are identified, and we use the NuSTAR data in combination with lower-energy X-ray observations (from Chandra, Swift XRT, and XMM-Newton) to characterize the broadband (0.5-24 keV) X-ray spectra. We find that all of the extreme sources are highly obscured AGNs, including three robust Compton-thick (CT; {N}<SUB>{{H</SUB>}}> 1.5× {10}<SUP>24</SUP> cm<SUP>-2</SUP>) AGNs at low redshift (z< 0.1) and a likely CT AGN at higher redshift (z = 0.16). Most of the extreme sources would not have been identified as highly obscured based on the low-energy (< 10 keV) X-ray coverage alone. The multiwavelength properties (e.g., optical spectra and X-ray-mid-IR luminosity ratios) provide further support for the eight sources being significantly obscured. Correcting for absorption, the intrinsic rest-frame 10-40 keV luminosities of the extreme sources cover a broad range, from ≈ 5× {10}<SUP>42</SUP> to 10<SUP>45</SUP> erg s<SUP>-1</SUP>. The estimated number counts of CT AGNs in the NuSTAR serendipitous survey are in broad agreement with model expectations based on previous X-ray surveys, except for the lowest redshifts (z< 0.07), where we measure a high CT fraction of {f}<SUB>{CT</SUB>}<SUP>{obs</SUP>}={30}<SUB>-12</SUB><SUP>+16</SUP> % . For the small sample of CT AGNs, we find a high fraction of galaxy major mergers (50% ± 33%) compared to control samples of “normal” AGNs. | URI: | http://hdl.handle.net/20.500.12386/26877 | URL: | https://iopscience.iop.org/article/10.3847/1538-4357/aa8176 | ISSN: | 0004-637X | DOI: | 10.3847/1538-4357/aa8176 | Bibcode ADS: | 2017ApJ...846...20L | Fulltext: | open |
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