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Date and Time of the Query: 2019-04-24 T19:25:38 PDT
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For refcode 2016ApJ...825...85K:
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2016ApJ...825...85K A New Population of Compton-thick AGNs Identified Using the Spectral Curvature above 10 keV Koss, Michael J.; Assef, R.; Balokovic, M.; Stern, D.; Gandhi, P.; Lamperti, I.; Alexander, D. M.; Ballantyne, D. R.; Bauer, F. E.; Berney, S.; Brandt, W. N.; Comastri, A.; Gehrels, N.; Harrison, F. A.; Lansbury, G.; Markwardt, C.; Ricci, C.; Rivers, E.; Schawinski, K.; Trakhtenbrot, B.; Treister, E.; Urry, C. Megan Abstract. We present a new metric that uses the spectral curvature (SC) above 10 keV to identify Compton-thick active galactic nuclei (AGNs) in low-quality Swift/Burst Alert Telescope (BAT) X-ray data. Using NuSTAR, we observe nine high SC-selected AGNs. We find that high-sensitivity spectra show that the majority are Compton-thick (78% or 7/9) and the remaining two are nearly Compton-thick (N_H_ ~= (5--8) x 10^23^ cm^-2^). We find that the SC_ BAT_ and SC_ NuSTAR_ measurements are consistent, suggesting that this technique can be applied to future telescopes. We tested the SC method on well-known Compton-thick AGNs and found that it is much more effective than broadband ratios (e.g., 100% using SC versus 20% using 8--24 keV/3--8 keV). Our results suggest that using the >10 keV emission may be the only way to identify this population since only two sources show Compton-thick levels of excess in the Balmer decrement corrected [O III] to observed X-ray emission ratio ({F}_[{{O_}{{III}}]}/{F}_2{--_10 {keV}}^{obs^}\gt 1) and WISE colors do not identify most of them as AGNs. Based on this small sample, we find that a higher fraction of these AGNs are in the final merger stage (<10 kpc) than typical BAT AGNs. Additionally, these nine obscured AGNs have, on average, ~4x higher accretion rates than other BAT-detected AGNs (< {lambda}_{Edd_}> \=\0.068+/- 0.023 compared to < {lambda}_{Edd_}> \=\0.016+/- 0.004). The robustness of SC at identifying Compton-thick AGNs implies that a higher fraction of nearby AGNs may be Compton-thick (~22%) and the sum of black hole growth in Compton-thick AGNs (Eddington ratio times population percentage) is nearly as large as mildly obscured and unobscured AGNs. Key words: galaxies: active, galaxies: Seyfert, X-rays: galaxies
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