Long Fading Mid-Infrared Emission in Transient Coronal Line Emitters: Dust Echo of Tidal Disruption Flare

TL;DR

This study reports the detection of long-lasting mid-infrared emission as an echo of tidal disruption events in galactic nuclei, revealing dust response to the flare over several years.

Contribution

It presents the first evidence of long-duration mid-IR echoes in TDE candidates, linking infrared emission to the tidal disruption flare in gas-rich environments.

Findings

Mid-IR emission lasts up to 14 years after TDE flare.

Dust temperatures decrease from 570K to 800K over time.

Estimated UV luminosity at peak ranges from 10^{44} erg/s.

Abstract

The sporadic accretion following the tidal disruption of a star by a super-massive black hole (TDE) leads to a bright UV and soft X-ray flare in the galactic nucleus. The gas and dust surrounding the black hole responses to such a flare with an echo in emission lines and infrared emission. In this paper, we report the detection of long fading mid-IR emission lasting up to 14 years after the flare in four TDE candidates with transient coronal lines using the WISE public data release. We estimate that the reprocessed mid-IR luminosities are in the range between $4\times 10^{42}$ and $2\times 10^{43}$ erg~s$^{-1}$ and dust temperature in the range of 570-800K when WISE first detected these sources three to five years after the flare. Both luminosity and dust temperature decreases with time. We interpret the mid-IR emission as the infrared echo of the tidal disruption flare. We estimate the UV luminosity at the peak flare to be 1 to 30 times $10^{44}$ erg s$^{-1}$ and for warm dust masses to be in the range of 0.05-1.3 Msun within a few parsecs. Our results suggest that the mid-infrared echo is a general signature of TDE in the gas-rich environment.