Infrared Echo and Late-stage Rebrightening of Nuclear Transient Ps1-10adi: Exploring the Torus with Tidal Disruption Events in Active Galactic Nuclei

Abstract

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.