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 M _ { \sun } within a few parsecs .
Our results suggest that the mid-infrared echo is a general signature of TDE in the gas-rich environment .