A deep X-ray view of the bare AGN Ark 120 VI. Geometry of the hot corona from spectroscopic and polarization signatures

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https://www.aanda.org/articles/aa/pdf/forth/aa34454-18.pdf

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http://hdl.handle.net/11603/12751

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UMBC Center for Space Sciences and Technology (CSST) / Center for Research and Exploration in Space Sciences & Technology II (CRSST II)

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2018-11-30

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journal articles postprints
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A. Marinucci, D. Porquet, F. Tamborra, S. Bianchi, V. Braito, A. Lobban, F. Marin, G. Matt, R. Middei, E. Nardini, J. Reeves and A. Tortosa, A deep X-ray view of the bare AGN Ark 120 VI. Geometry of the hot corona from spectroscopic and polarization signatures, Astronomy & Astrophysics manuscript no. ark120_papVI, 2018 , https://www.aanda.org/articles/aa/pdf/forth/aa34454-18.pdf

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Subjects

galaxies:active
galaxies: seyfert
galaxies: accretion
individual: ark 120

Abstract

Context. The spectral shape of the hard X-ray continuum of active galactic nuclei (AGN) can be ascribed to inverse Compton scattering of optical/UV seed photons from the accretion disc by a hot corona of electrons. This physical process produces a polarization signal which is strongly sensitive to the geometry of the scattering medium (i.e., the hot corona) and of the radiation field. Aims. MoCA (Monte Carlo code for Comptonisation in Astrophysics) is a versatile code which allows for di erent geometries and configurations to be tested for Compton scattering in compact objects. A single photon approach is considered as well as polarisation and Klein-Nishina e ects. For this work, we selected four di erent geometries for the scattering electrons cloud above the accretion disc, namely an extended slab, an extended spheroid and two compact spheroids. Methods. We discuss the first application of the MoCA model to reproduce the hard X-ray primary continuum of the bare Seyfert 1 galaxy Ark 120, using different geometries for the hot corona above the accretion disc. The lack of extragalactic absorption along the line of sight makes it an excellent target for studying the accretion disc-corona system. We report on the spectral analysis of the simultaneous 2013 and 2014 XMM-Newton and NuSTAR observations of the source. Results. A general agreement is found between the best fit values of the hot coronal parameters obtained with MoCA and those inferred using other Comptonisation codes from the literature. The expected polarization signal from the best fits with MoCA is then presented and discussed, in view of the launch in 2021 of the Imaging X-ray Polarimetry Explorer (IXPE). Conclusions. We find that none of the tested geometries for the hot corona (extended slab and extended or compact spheroids) can be statistically preferred, based on spectroscopy solely. In the future, an IXPE observation less than 1 Ms long will clearly distinguish between an extended slab or a spherical hot corona.