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 tentatively been investigated recently. We report the discovery of a long-lasting luminous mid-infrared (mid-IR) flare in PS1-10adi, which is a newly-identified highly energetic transient event occurred in AGN. The IR luminosity of PS1-10adi, as well as other analogous events, are at least one order of magnitude higher than all known supernova, but can be well interpreted as the dust echoes of TDEs, whose ultra-high 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 lead 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 is also an intriguing feature of PS1-10adi, which could be attributed to the interaction between the high-velocity outflow and 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.

An extremely energetic supernova from a very massive star in a dense medium

“…Another discriminant between SN2016aps and this population of nuclear transients is the lack of a mid-IR echo. All of these event studied to date [8], including PS16dtm [7], have shown very bright mir-IR emission, detected by the Wide-field Infrared Survery Explorer (WISE), following the optical flare [91]. This has been interpreted [91] as a TDE signature, as the mid-IR luminosity in these events is challenging to produce with a SN, but consistent with a dusty AGN torus.…”

A Mid-infrared Flare in the Active Galaxy MCG-02-04-026: Dust Echo of a Nuclear Transient Event

“…Blanchard et al (2017) found that PS16dtm, a transient event hosted in a narrow-line Seyfert 1 galaxy with existing Fe II emission, enhanced the Fe II emission in half a year after the transient event's flux peaks. Also, Jiang et al (2019) noticed that along with PS1-10adi, transient Fe II emission increased rapidly around the time of the optical maximum and disappeared in an observation 3.5 yr later. These transient Fe II emissions that varied on a timescale of years were interpreted as the radiation of Fe elements in the dust clouds that is released from the solid state into the gas state under UV photons (Jiang et al 2019).…”

“…Also, Jiang et al (2019) noticed that along with PS1-10adi, transient Fe II emission increased rapidly around the time of the optical maximum and disappeared in an observation 3.5 yr later. These transient Fe II emissions that varied on a timescale of years were interpreted as the radiation of Fe elements in the dust clouds that is released from the solid state into the gas state under UV photons (Jiang et al 2019). They are the observational evidence of the dust sublimation in the model.…”

“…Many of the transient events in active galaxies are accompanied by mid-infrared (MIR) flares. The examples are CSS100217:102913+404220 (Jiang et al 2019), PS16dtm (Jiang et al 2017), F01004-2237 (Dou et al 2017), PS1-10adi (Kankare et al 2017), W0948+0318 (Assef et al 2018), and OGLE17aaj (Yang et al 2019). The MIR flares were observed by an all-sky time-domain survey in the MIR band named the Wide field Infrared Survey Explorer (WISE), which we will introduce in detail later.…”

“…We are conducting a comprehensive search of MIR flares in nearby Sloan Digital Sky Survey (SDSS) spectroscopic galaxies using WISE data (Jiang et al 2020). We found several tens of MIR flares.…”