Abstract :
[en] Active galactic nuclei (AGN) emit radiation via accretion across the entire energy spectrum. While the standard disk and corona model can somewhat describe this emission, it fails to predict specific features such as the soft X-ray excess, the short-term optical/UV variability, and the observed UV/X-ray correlation in AGN. In this context, the fraction of AGN emission in different bands (i.e., bolometric corrections) can be useful to better understand the accretion physics of AGN. Past studies have shown that the X-ray bolometric corrections are strongly dependent on the physical properties of AGN, such as their luminosities and Eddington ratios. However, since these two parameters depend on each other, it has been unclear which is the main driver of the X-ray bolometric corrections. We present here results from a large study of hard-X-ray-selected (14-195 keV) nearby (z < 0.1) AGN. Based on our systematic analysis of the simultaneous optical-to-X-ray spectral energy distributions of 236 unobscured AGN, we found that the primary parameter controlling the X-ray bolometric corrections is the Eddington ratio. Our results show that, while the X-ray bolometric correction increases with the bolometric luminosity for sources with intermediate Eddington ratios (0.01-1), this dependence vanishes for sources with lower Eddington ratios (<0.01). This could be used as evidence for a change in the accretion physics of AGN at low Eddington ratios.
Funding text :
We thank the anonymous referee for providing insightful comments that improved this manuscript. 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. We acknowledge the usage 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. We acknowledge financial support from: a 2018 grant from the ESO-Government of Chile Joint Committee (K.K.G.); the Belgian Federal Science Policy Office (BELSPO) for the provision of financial support in the framework of the PRODEX Programme of the European Space Agency (K.K.G.); ANID CATA-BASAL project FB210003 (C.R., F.E.B., and E.T.); ANID FONDECYT Regular grant #1230345 (C.R.), #1241005 (F.E.B. and E.T.), #1250821 (F.E.B. and E.T.), and #1200495 (E.T.); ANID Millennium Science Initiative\u2014AIM23-0001 (F.E.B.); NASA ADAP award 80NSSC19K0749 (M.J.K.); Fondecyt Postdoctoral Fellowship #3220516 (M.J.T.), #3230310 (Y.D.), #3230303 (A.J.), and #3230653 (I.M.C.); STFC #ST/X001075/1 (M.J.T.). C.R. acknowledges support from the China-Chile joint research fund. B.T. acknowledges support from the European Research Council under the European Union\u2019s Horizon 2020 research and innovation program (grant agreement #950533) and from the Israel Science Foundation (grant #1849/19). This research was supported by the Excellence Cluster ORIGINS, which is funded by the Deutsche Forschungsgemeinschaft (DFG; German Research Foundation) under Germany\u2019s Excellence Strategy\u2014EXC 2094\u2014390783311. B.T. also acknowledges the hospitality of the Instituto de Estudios Astrof\u00ECsicos at Universidad Diego Portales, and of the Instituto de Astrof\u00ECsica at Pontificia Universidad Cat\u00F3lica de Chile. K.O. acknowledges support from the Korea Astronomy and Space Science Institute under the R&D program (Project #2025-1-831-01), supervised by the Korea AeroSpace Administration, and the National Research Foundation of Korea grant funded by the Korea government (MSIT; RS-2025-00553982).
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