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The presence of an obscuring torus at parsec-scale distances from the central black hole is the main ingredient for the Unified Model of active galactic nuclei (AGN), as obscured sources are thought to be seen through this structure. However, the Unified Model fails to describe a class of sources that undergo dramatic spectral changes, transitioning from obscured to unobscured and vice versa through time. The variability in these sources, which are known as changing-look AGN (CLAGN), is thought to be produced by a clumpy medium at much smaller distances than the conventional obscuring torus. ESO 323-G77 is a CLAGN that was observed in various states through the years with Chandra, Suzaku, Swift-XRT, and XMM-Newton, from unobscured (NH < 31022 cm2) to Compton-thin (NH ~ 16 1023 cm2) and even Compton-thick (NH > 1 1024 cm2), on timescales as short as one month. We present an analysis of the first NuSTAR monitoring of ESO 323-G77, consisting of five observations taken at different timescales (1, 2, 4, and 8 weeks from the first one) in 2016-2017, in which the AGN was caught in a persistent Compton-thin obscured state (NH ~ 24 1023 cm2). We find that a Compton-thick reflector is present (NH;refl = 5 1024 cm), most likely associated with the presence of the putative torus. Two ionized absorbers are unequivocally present, located within maximum radii of rmax;1 = 1:5 pc and rmax;2 = 0:01 pc. In one of the observations, the inner ionized absorber is blueshifted, indicating the presence of a possible faster (vout = 0:2c) ionized absorber, marginally detected at 3. Finally, we are able to constrain the coronal temperature and the optical depth of ESO 323-G77, obtaining kTe = 38 keV or kTe = 36 keV, and = 1:4 or = 2:8, depending on the coronal geometry assumed. [ABSTRACT FROM AUTHOR]

According to theory, the torus of active galactic nuclei (AGN) is sustained from a wind coming off the accretion disc, and for low efficient AGN, it has been proposed that such structure disappears. However, the exact conditions for its disappearance remain unclear. This can be studied throughout the reflection component at X-rays, which is associated with distant and neutral material at the inner walls of the torus in obscured AGN. We select a sample of 81 AGNs observed with NuSTAR with a distance limit of D< 200 Mpc and Eddington rate |$\rm {\lambda _{Edd} \equiv L_{bol}/L_{Edd}\lt 10^{-3}}$|⁠. We fit the 3–70 keV spectra using a model accounting for a partial-covering absorber plus a reflection component from neutral material. We find that the existence of the reflection component spans in a wide range of black hole mass and bolometric luminosities, with only ∼13 per cent of our sample (11 sources) lacking of any reflection signatures. These sources fall in the region in which the torus may be lacking in the L-MBH diagram. For the sources with a detected reflection component, we find that the vast majority of them are highly obscured (⁠|$\rm {\log \ N_H \gt 23}$|⁠), with |$\rm {\sim 20{{\ \rm per\ cent}}}$| being Compton-thick. We also find an increase in the number of unobscured sources and a tentative increase on the ratio between |$\rm {FeK\alpha }$| emission line and Compton-hump luminosities toward |$\rm {\lambda _{Edd}=10^{-5}}$|⁠ , suggesting that the contribution of the |$\rm {FeK\alpha }$| line changes with Eddington ratio. [ABSTRACT FROM AUTHOR]

Tidal disruption events (TDEs) that occur in active galactic nuclei (AGNs) with dusty tori are a special class of sources. TDEs can generate ultrafast and large opening-angle wind, which will almost inevitably collide with the pre-existing AGN dusty tori a few years later after the TDE outburst. The wind–torus interactions drive two kinds of shocks: the bow shocks at the windward side of the torus clouds, and the cloud shocks inside the torus clouds. In a previous work, we proved that the shocked clouds will give rise to considerable X-ray emissions which can reach 1041 − 42 erg s−1 (so called years delayed X-ray afterglows). In this work, we focus on the radiations of high energy particles accelerated at both shocks. Benefiting from the strong radiation field at the inner edge of the torus, the inverse Compton scatterings of AGN photons by relativistic electrons at bow shocks dominate the overall gamma-ray radiation. The gamma-ray luminosity can reach |$10^{41}~{\rm erg~s^{-1}}(L_{\rm kin}/10^{45}\, {\rm erg \, s^{-1}})$|⁠ , where L kin is the kinetic luminosity of TDE wind. Synchrotron radiation at bow shocks contributes to the radio afterglow with a luminosity of 10 |$^{38-39} ~{\rm erg~s^{-1}}(L_{\rm kin}/10^{45}\, {\rm erg \, s^{-1}})$| at 1–10 GHz if the magnetic field is 100 mGauss, and extends to infrared with a luminosity of |$\sim 10^{39-40}~{\rm erg \, s^{-1}} (L_{\rm kin}/10^{45}\, {\rm erg \, s^{-1}})$|⁠. Our scenario provides a prediction of the years delayed afterglows in multiple wavebands for TDEs and reveals their connections. [ABSTRACT FROM AUTHOR]