BAT AGN Spectroscopic Survey XXVII: scattered X-Ray radiation in obscured active galactic nuclei

Creators: Gupta, K. K.; Ricci, C.; Tortosa, A.; Ueda, Y.; Kawamuro, T.; Koss, M.; Trakhtenbrot, B.; Oh, K.; Bauer, F. E.; Ricci, F.; Privon, G. C.; Zappacosta, L.; Stern, D.; Kakkad, D.; Piconcelli, E.; Veilleux, S.; Mushotzky, R.; Caglar, T.; Ichikawa, K.; Elagali, A.; Powell, M. C.; Urry, C. M.; Harrison, F.

Abstract

Accreting supermassive black holes (SMBHs), also known as active galactic nuclei (AGN), are generally surrounded by large amounts of gas and dust. This surrounding material reprocesses the primary X-ray emission produced close to the SMBH and gives rise to several components in the broadband X-ray spectra of AGN, including a power-law possibly associated with Thomson-scattered radiation. In this work, we study the properties of this scattered component for a sample of 386 hard-X-ray-selected, nearby (⁠z∼0.03⁠) obscured AGN from the 70-month Swift/BAT catalogue. We investigate how the fraction of Thomson-scattered radiation correlates with different physical properties of AGN, such as line-of-sight column density, X-ray luminosity, black hole mass, and Eddington ratio. We find a significant negative correlation between the scattering fraction and the column density. Based on a large number of spectral simulations, we exclude the possibility that this anticorrelation is due to degeneracies between the parameters. The negative correlation also persists when considering different ranges of luminosity, black hole mass, and Eddington ratio. We discuss how this correlation might be either due to the angle dependence of the Thomson cross-section or to more obscured sources having a higher covering factor of the torus. We also find a positive correlation between the scattering fraction and the ratio of [O III] λ5007 to X-ray luminosity. This result is consistent with previous studies and suggests that the Thomson-scattered component is associated with the narrow-line region.

Additional Information

© 2021 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model). Accepted 2021 March 15. Received 2021 February 16; in original form 2020 November 19. Published: 24 March 2021. We would like to thank the anonymous referee for the prompt and constructive report that strengthened this paper. We thank Matthew Temple for his valuable comments. This work made use of data from the NASA/IPAC Infrared Science Archive and NASA/IPAC Extragalactic Database (NED), which are operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This research has made use of data and/or software provided by the High Energy Astrophysics Science Archive Research Center (HEASARC), which is a service of the Astrophysics Science Division at NASA/GSFC and the High Energy Astrophysics Division of the Smithsonian Astrophysical Observatory. KKG was supported by a 2018 grant from the ESO – Government of Chile Joint Committee. We acknowledge support from FONDECYT Iniciacion grant 11190831 (CR), ANID grants CATA-Basal AFB-170002 (FEB), FONDECYT Regular 1190818 and 1200495 (FEB), and Millennium Science Initiative ICN12_009 (FEB). MK acknowledges support from NASA through ADAP award 80NSSC19K0749. KO acknowledges support from the National Research Foundation of Korea (NRF-2020R1C1C1005462). EP acknowledges financial support under ASI/INAF contract 2017-14-H.0. Data Availability: The data underlying this article are available in Ricci et al. (2017a), Koss et al. (2017), Koss et al. (in preparation), and Oh et al. (in preparation). Additional data will be shared on a reasonable request to the corresponding author.

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