Hot Coronae in Local AGN: Present Status and Future Perspectives

Abstract

The nuclear X-ray emission in radio-quiet Active Galactic Nuclei (AGN) is commonly believed to be due to inverse Compton scattering of soft UV photons in a hot corona. The radiation is expected to be polarized, the polarization degree depending mainly on the geometry and optical depth of the corona. Nuclear Spectroscopic Telescope Array (NuSTAR) observations are providing for the first time high quality measurements of the coronal physical parameters-temperature and optical depth. We hereby review the NuSTAR results on the coronal physical parameters (temperature and optical depth) and discuss their implications for future X-ray polarimetric studies.

Spectral and polarization properties of reflected X-ray emission from black-hole accretion discs for a distant observer: the lamp-post model

“…In this section, we plan to discuss the impact of variable incident polarization that we studied in semi-realistic conditions of p 0 = 0 (purple lines in figures), p 0 = 0.01 and χ 0 = 0 • (green lines in figures), p 0 = 0.01 and χ 0 = 90 • (orange lines in figures; Beheshtipour et al 2017 ;Beheshtipour 2018 ;Tamborra et al 2018 ). But we note that KYNSTOKES allows for studies of arbitrary primary polarization state, which is calculated at the disc from the 0 per cent and 100 per cent polarized local reflection tables through ( 2 ).…”

“…Staying in the lamp-post scheme, which itself is a simplified concept (see e.g. Kubota & Done 2018 ;Marinucci et al 2018 ;Poutanen et al 2018 ), we may first develop the non-isotropic lamp-post emission. This would certainly impro v e precision in polarization quantities, especially for the reflected component, because the disc is expected to recei ve v ariable flux and polarization, depending on each position and each incident angle.…”

“…MNRAS 524, 3853-3876 (2023) processed by the disc or by more distant components of the system. The primary X-rays can already obtain partial scattering-induced polarization ( 10 per cent ) in the corona (Poutanen & Svensson 1996 ;Schnittman & Krolik 2010 ;Beheshtipour, Krawczynski & Malzac 2017 ;Beheshtipour 2018 ;Marinucci et al 2018 ;Tamborra et al 2018 ;Krawczynski & Beheshtipour 2022 ;Krawczynski et al 2022 ;Ursini et al 2022 ;Poutanen, Veledina & Beloborodov 2023 ). Our objective is to focus on the reflection of the X-ray powerlaw emission from the accretion disc and to discuss spectral and polarization signatures of such radiation for a distant observer, i.e.…”

“…The integration and ray-tracing processes require choosing some prescribed simple coronal geometry, which is until today one of the main unknowns of such modeling (see e.g. Kubota & Done 2018 ; Marinucci et al 2018 ;Poutanen, Veledina & Zdziarski 2018 ). Several global geometries of the corona can be considered.…”

“…Other classes of models assume e.g. the extended corona (Haardt & Maraschi 1991 ;Haardt 1993 ;Poutanen & Svensson 1996 ;Dabrowski & Lasenby 2001 ;Malzac, Dumont & Mouchet 2005 ;Nied źwiecki & Życki 2008 ;Schnittman & Krolik 2010 ;Marinucci et al 2018 ;Poutanen et al 2018 ; a diffuse optically thin hot corona near abo v e large area of the disc ranging from slab to spherical assumptions) or a truncated inner accretion disc (i.e. not extending to the innermost stable circular orbit) with the so-called hot inner accretion flow , which can be divided into sub-classes based on plasma interaction of the hot flow with the inner edge of the cold disc (Poutanen & Svensson 1996 ;Do v e et al 1997 ;Esin, McClintock & Narayan 1997 ;Esin et al 1998 ;Zdziarski et al 1998 ;Liu et al 2007 ;Poutanen & Vurm 2009 ;Veledina, Poutanen & Vurm 2013 ;Poutanen et al 2018 ).…”