Tidal disruption events (TDEs) in active galactic nuclei (AGNs) have been overlooked for a long time but have recently been tentatively investigated. We report the discovery of a long-lasting, luminous mid-infrared (mid-IR) flare in PS1-10adi, which is a newly identified and highly energetic transient event occurring in an AGN. The IR luminosity of PS1-10adi, as well as other analogous events, is at least one order of magnitude higher than that of all known supernova, but can be well interpreted as the dust echoes of TDEs, whose ultrahigh IR energy is reprocessed from the dusty torus around the black hole. The torus dust is sublimating during the early stage of the outburst and probably leads to the observed rapid emergence of Fe ii lines. Moreover, the UV-optical rebrightening and contemporaneous X-ray onset after ∼1500 rest-frame days since the optical peak are also an intriguing feature of PS1-10adi that can be attributed to the interaction between the high-velocity outflow and the torus. We suggest that the luminous IR echo is a very typical phenomenon of TDEs in AGNs and may provide us an ideal opportunity to explore the torus properties.

Quasar outflows may play a crucial role in regulating the host galaxy, although the spatial scale of quasar outflows remain a major enigma, with their acceleration mechanism poorly understood. The kinematic information of outflow is the key to understanding its origin and acceleration mechanism. Here, we report the galactocentric distances of different outflow components for both a sample and an individual quasar. We find that the outflow distance increases with velocity, with a typical value from several parsecs to more than one hundred parsecs, providing direct evidence for an acceleration happening at a scale of the order of 10 parsecs. These outflows carry ∼1% of the total quasar energy, while their kinematics are consistent with a dust-driven model with a launching radius comparable to the scale of a dusty torus, indicating that the coupling between dust and quasar radiation may produce powerful feedback that is crucial to galaxy evolution.

Tidal disruption event (TDE) can launch an ultrafast outflow. If the black hole is surrounded by large amounts of clouds, outflow–cloud interaction will generate bow shocks, accelerate electrons, and produce radio emission. Here, we investigate the interaction between a non-relativistic outflow and clouds in active galaxies, which is manifested as outflow–BLR (broad-line region) interaction, and can be extended to outflow–torus interaction. This process can generate considerable radio emission, which may account for the radio flares appearing a few months later after TDE outbursts. Benefitting from efficient energy conversion from outflow to shocks and the strong magnetic field, outflow–cloud interaction may play a non-negligible, or even dominating role in generating radio flares in a cloudy circumnuclear environment if the CNM density is no more than 100 times the Sgr A*-like one. In this case, the evolution of radio spectra can be used to directly constrain the properties of outflows.

A tidal disruption event (TDE), AT2019dsg, was observed to be associated with a PeV neutrino event, IceCube-191001A, lagging the optical outburst by a half year. It is known that TDEs may generate ultrafast outflows. If the TDE occurs in a cloudy environment, the outflow-cloud interactions may form shock waves which generate accelerated protons and hence delayed neutrinos from hadronic interactions in clouds. Here we investigate the neutrino production in AT2019dsg by examining the TDE outflow-cloud interaction model. We find that, for an outflow with a velocity of 0.07c and a kinetic luminosity of |$10^{45}\rm erg\ s^{-1}$|⁠, protons may be accelerated up to ∼ 60 PeV by the bow shocks, and generate PeV neutrinos by interactions with clouds. The predicted neutrino number in this model depends on the uncertainties of model parameters and in order to match the observations, some challenging values of parameters have been involved. The PeV neutrino event number can be ∼4 × 10⁻³ for a hard proton index Γ = 1.5.

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 10^41 − 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.