We identify sources with extremely hard X-ray spectra (i.e., with photon indices of G<=0.6) in the 13 deg2 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; NH>1.5 1E24 cm-2) 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 5E42 to 1045 erg s-1. 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 fCT obs = 30% -12+16 . 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.
Lansbury G.B., Alexander D.M., Aird J., Gandhi P., Stern D., Koss M., et al. (2017). The NuSTAR Serendipitous Survey: Hunting for the Most Extreme Obscured AGN at >10 keV. THE ASTROPHYSICAL JOURNAL, 846(1), 1-19 [10.3847/1538-4357/aa8176].
The NuSTAR Serendipitous Survey: Hunting for the Most Extreme Obscured AGN at >10 keV
Marchesi S.Writing – Review & Editing
;
2017
Abstract
We identify sources with extremely hard X-ray spectra (i.e., with photon indices of G<=0.6) in the 13 deg2 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; NH>1.5 1E24 cm-2) 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 5E42 to 1045 erg s-1. 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 fCT obs = 30% -12+16 . 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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
