NASA/IPAC EXTRAGALACTIC DATABASE
Date and Time of the Query: 2019-06-18 T17:46:53 PDT
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For refcode 2016ApJ...826...93B:
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Copyright by American Astronomical Society. Reproduced by permission
2016ApJ...826...93B A Growth-rate Indicator for Compton-thick Active Galactic Nuclei Brightman, M.; Masini, A.; Ballantyne, D. R.; Balokovic, M.; Brandt, W. N.; Chen, C.-T.; Comastri, A.; Farrah, D.; Gandhi, P.; Harrison, F. A.; Ricci, C.; Stern, D.; Walton, D. J. Abstract. Due to their heavily obscured central engines, the growth rate of Compton-thick (CT) active galactic nuclei (AGNs) is difficult to measure. A statistically significant correlation between the Eddington ratio, lambda_Edd_, and the X-ray power-law index, Gamma, observed in unobscured AGNs offers an estimate of their growth rate from X-ray spectroscopy (albeit with large scatter). However, since X-rays undergo reprocessing by Compton scattering and photoelectric absorption when the line of sight to the central engine is heavily obscured, the recovery of the intrinsic Gamma is challenging. Here we study a sample of local, predominantly CT megamaser AGNs, where the black hole mass, and thus Eddington luminosity, are well known. We compile results of the X-ray spectral fitting of these sources with sensitive high-energy (E > 10 keV) NuSTAR data, where X-ray torus models, which take into account the reprocessing effects have been used to recover the intrinsic Gamma values and X-ray luminosities, L_X_. With a simple bolometric correction to L_X_ to calculate lambda_Edd_, we find a statistically significant correlation between Gamma and lambda_Edd_ (p = 0.007). A linear fit to the data yields Gamma = (0.41 +/- 0.18)log_10_ lambda_Edd_ + (2.38 +/- 0.20), which is statistically consistent with results for unobscured AGNs. This result implies that torus modeling successfully recovers the intrinsic AGN parameters. Since the megamasers have low-mass black holes (M_BH_ ~ 10^6^--10^7^ M_sun_) and are highly inclined, our results extend the Gamma--lambda_Edd_ relationship to lower masses and argue against strong orientation effects in the corona, in support of AGN unification. Finally this result supports the use of Gamma as a growth-rate indicator for accreting black holes, even for CT AGNs. Key words: black hole physics, galaxies: general, galaxies: nuclei, galaxies: Seyfert, masers
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