Observational hints on the torus obscuring gas behaviour through X-rays with NuSTAR data

Author:

Osorio-Clavijo N1ORCID,González-Martín O1,Sánchez S F2,Esparza-Arredondo D1,Masegosa J3,Victoria-Ceballos C1,Hernández-García L45,Díaz Y5

Affiliation:

1. Instituto de Radioastronomía and Astrofisica (IRyA-UNAM), 3-72 (Xangari), 8701 Morelia, Mexico

2. Instituto de Astronomía, Universidad Nacional Autónoma de México, A. P. 70-264, C.P. 04510 México, D.F., Mexico

3. IAA - Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astonomía, E-18008 Granada, Spain

4. Millennium Institute of Astrophysics (MAS), Nuncio Monseñor Sótero Sanz 100, Providencia, Santiago, Chile

5. Instituto de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Gran Bretaña 1111, Playa Ancha, Valparaíso, Chile

Abstract

ABSTRACT According to theory, the torus of active galactic nuclei (AGN) is sustained from a wind coming off the accretion disc, and for low efficient AGN, it has been proposed that such structure disappears. However, the exact conditions for its disappearance remain unclear. This can be studied throughout the reflection component at X-rays, which is associated with distant and neutral material at the inner walls of the torus in obscured AGN. We select a sample of 81 AGNs observed with NuSTAR with a distance limit of D< 200 Mpc and Eddington rate $\rm {\lambda _{Edd} \equiv L_{bol}/L_{Edd}\lt 10^{-3}}$. We fit the 3–70 keV spectra using a model accounting for a partial-covering absorber plus a reflection component from neutral material. We find that the existence of the reflection component spans in a wide range of black hole mass and bolometric luminosities, with only ∼13 per cent of our sample (11 sources) lacking of any reflection signatures. These sources fall in the region in which the torus may be lacking in the L-MBH diagram. For the sources with a detected reflection component, we find that the vast majority of them are highly obscured ($\rm {\log \ N_H \gt 23}$), with $\rm {\sim 20{{\ \rm per\ cent}}}$ being Compton-thick. We also find an increase in the number of unobscured sources and a tentative increase on the ratio between $\rm {FeK\alpha }$ emission line and Compton-hump luminosities toward $\rm {\lambda _{Edd}=10^{-5}}$, suggesting that the contribution of the $\rm {FeK\alpha }$ line changes with Eddington ratio.

Funder

UNAM

ANID

Publisher

Oxford University Press (OUP)

Subject

Space and Planetary Science,Astronomy and Astrophysics

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