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The circumnuclear material around active galactic nuclei (AGNs) is one of the essential components of the obscuration-based unification model. However, our understanding of the circumnuclear material in terms of its geometrical shape, structure, and its dependence on accretion rate is still debated. In this paper, we present the multi-epoch broad-band X-ray spectral modelling of a nearby Compton-thick AGN in Circinus galaxy. We utilize all the available hard X-ray (>10 keV) observations taken from different telescopes, i.e. BeppoSAX, Suzaku, NuSTAR , and AstroSat , at 10 different epochs across 22 yr from 1998 to 2020. The 3.0–79 keV broad-band X-ray spectral modelling using physically motivated models, namely MYTorus, borus02 , and uxclumpy , infers the presence of a torus with a low covering factor of 0.28, an inclination angle of 77°–81° and Compton-thick line-of-sight column densities (N H,LOS = 4.13–9.26 × 1024 cm−2) in all the epochs. The joint multi-epoch spectral modelling suggests that the overall structure of the torus is likely to remain unchanged. However, we find tentative evidence for the variable line-of-sight column density on time-scales ranging from 1 d to 1 week to a few years, suggesting a clumpy circumnuclear material located at subparsec to tens of parsec scales. [ABSTRACT FROM AUTHOR]

We present a detailed study of the highly obscured active galaxy NGC 4507, performed using four Nuclear Spectroscopic Telescope Array (NuSTAR) observations carried out between May and August in 2015 (∼130 ks in total). Using various phenomenological and physically motivated torus models, we explore the properties of the X-ray source and those of the obscuring material. The primary X-ray emission is found to be non-variable, indicating a stable accretion during the period of the observations. We find the equatorial column density of the obscuring materials to be ∼2 × 1024 cm−2 while the line-of-sight column density to be ∼7–8 × 1023 cm−2. The source is found to be deeply buried with the torus covering factor of ∼0.85. We observe variability in the line-of-sight column density on a time-scale of <35 d. The covering factor of the Compton-Thick material is found to be ∼0.35 in agreement with the results of recent X-ray surveys. From the variability of the line-of-sight column density, we estimate that the variable absorbing material is likely located either in the BLR or in the torus. [ABSTRACT FROM AUTHOR]

Reprocessed X-ray emission in active galactic nuclei can provide fundamental information about the circumnuclear environments of supermassive black holes. Recent mid-infrared studies have shown evidence of an extended dusty structure perpendicular to the torus plane. In this work, we build a self-consistent X-ray model for the Circinus Galaxy including the different physical components observed at different wavelengths and needed to reproduce both the morphological and spectral properties of this object in the mid-infrared. The model consists of four components: the accretion disc, the broad-line region (BLR), a flared disc in the equatorial plane, and a hollow cone in the polar direction. Our final model reproduces well the 3–70 keV Chandra and NuSTAR spectra of Circinus, including the complex Fe Kα zone and the spectral curvature, although several additional Gaussian lines, associated with either ionized iron or broadened Fe Kα/Kβ lines, are needed. We find that the flared disc is Compton-thick (⁠|$N_{\rm H,d}= \rm 1.01^{+0.03}_{-0.24}\times 10^{25}\, cm^{-2}$|⁠) and geometrically thick (⁠|$\mathrm{ CF}=0.55^{+0.01}_{-0.05}$|⁠), and that the hollow cone has a Compton-thin column density (⁠|$N_{\rm H,c}= \rm 2.18^{+0.47}_{-0.43}\times 10^{23}\, cm^{-2}$|⁠), which is consistent with the values inferred by mid-infrared studies. Including also the BLR, the effective line-of-sight column density is |$N_{\rm H}= \rm 1.47^{+0.03}_{-0.24}\times 10^{25}\, cm^{-2}$|⁠. This approach to X-ray modelling, i.e. including all the different reprocessing structures, will be very important to fully exploit data from future X-ray missions. [ABSTRACT FROM AUTHOR]