NuSTAR Measurement of Coronal Temperature in Two Luminous, High-redshift Quasars

Abstract

X-ray emission from AGN is believed to be produced via Comptonization of optical/UV seed photons emitted by the accretion disk, up-scattered by hot electrons in a corona surrounding the black hole. A critical compactness vs. temperature threshold is predicted above which any increase in the source luminosity, for a fixed size, would then generate positron-electron pairs rather than continue heating the coronal plasma. Current observations seem to confirm that all AGN populate the region below this critical line. These models, however, have never been probed by observations in the high-luminosity regime, where the critical line is expected to reach low temperatures. To fill this observational gap, we selected two luminous (log(L Bol )> 47.5 erg/s) quasars, 2MASSJ1614346+470420 (z=1.86) and B1422+231 (z=3.62), and obtained XMM-Newton and NuSTAR deep observations for them. We performed detailed spectral analysis of their quasi-simultaneous soft and hard Xray data, in order to constrain the parameters of their coronae. Using a phenomenological cut-off power-law model, with the inclusion of a reflection component, we derived rest-frame values of the high energy cut-off of E cut = 106 +102 −37 keV and E cut = 66 +17 −12 keV, respectively. Comptonization models consistently give as best-fit parameters electron temperatures of ∼ 45 keV and ∼ 28 keV, respectively, and optically thick coronae (τ > 1). These low coronal temperatures fall in the limited region allowed at these luminosities to avoid runaway pair production.

NuSTAR Survey of Obscured Swift/BAT-selected Active Galactic Nuclei: II. Median High-energy Cutoff in Seyfert II Hard X-ray Spectra

“…ward comparison between coronae of obscured and unobscured AGN, their physical properties, and possibly scaling relations and evolution (e.g., Kammoun et al 2017, Lanzuisi et al 2019. More similar studies are expected in the future based on NuSTAR data, though higher sensitivity and higher-energy coverage of the proposed missions HEX-P (Madsen et al 2018(Madsen et al , 2019 or FORCE (Nakazawa et al 2018) will be needed in order to reach large AGN samples and detailed coronal physics (Kamraj et al 2019).…”

NuSTAR Survey of Obscured Swift/BAT-selected Active Galactic Nuclei. II. Median High-energy Cutoff in Seyfert II Hard X-Ray Spectra

“…physically motivated spectral models for coronal emission. This will enable more straightforward comparison between coronae of obscured and unobscured AGNs, their physical properties, and possibly scaling relations and evolution (e.g., Kammoun et al 2017;Lanzuisi et al 2019). More similar studies are expected in the future based on NuSTAR data, though higher-sensitivity and higher-energy coverage of the proposed missions HEX-P (Madsen et al 2018(Madsen et al , 2019 or FORCE (Nakazawa et al 2018) will be needed in order to reach large AGN samples and detailed coronal physics (Kamraj et al 2019 We have made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration.…”

The X-ray emission of the Seyfert 2 galaxy MCG-01-24-12

“…Rybicki & Lightman 1979;Beloborodov 1999;Petrucci et al 2000Petrucci et al , 2001Ghisellini 2013;Middei et al 2019). The relations between Γ-E c and kT e -τ e have been recently derived by Middei et al (2019) that used extensive simulations computed with MoCA (Monte Carlo code for Comptonisation in Astrophysics, Tamborra et al 2018) for studying the Comptonised spectrum of AGNs (see also Marinucci et al 2019;Lanzuisi et al 2019, for further applications of this code). In particular, using Eqs.…”