A Growth-rate Indicator for Compton-thick Active Galactic Nuclei

Brightman, M.M.BrightmanMasini, A.A.MasiniBallantyne, D. R.D. R.BallantyneBaloković, M.M.BalokovićBrandt, W. N.W. N.BrandtChen, C. -T.C. -T.ChenCOMASTRI, AndreaAndreaCOMASTRIFarrah, D.D.FarrahGandhi, P.P.GandhiHarrison, F. A.F. A.HarrisonRicci, C.C.RicciStern, D.D.SternWalton, D. J.D. J.Walton2020-05-152020-05-1520160004-637Xhttp://hdl.handle.net/20.500.12386/24893Due 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, λ Edd, and the X-ray power-law index, Γ, 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 Γ 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 Γ values and X-ray luminosities, L X. With a simple bolometric correction to L X to calculate λ Edd, we find a statistically significant correlation between Γ and λ Edd (p = 0.007). A linear fit to the data yields Γ = (0.41 ± 0.18)log10 λ 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 ≈ 106-107 M ☉) and are highly inclined, our results extend the Γ-λ 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 Γ as a growth-rate indicator for accreting black holes, even for CT AGNs.ELETTRONICOenA Growth-rate Indicator for Compton-thick Active Galactic NucleiArticle10.3847/0004-637X/826/1/932-s2.0-84994323462000381962200093https://iopscience.iop.org/article/10.3847/0004-637X/826/1/93https://iopscience.iop.org/article/10.3847/0004-637X/826/1/93/pdf2016ApJ...826...93BFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation