Program: GN-2022B-Q-122

We serendipitously discovered an exceptional MIR flare at the center of NGC 3786 that occurred in late-2020 using multi-epoch data from WISE. Intriguingly, there was no optical variability corresponding to MIR flare as if the event is obscured by a dusty torus, although NGC 3786 hosts a type 1.8/1.9 AGN. As a rising time scale of the transient is relatively short and the W1-W2 color becomes redder as it brightens, this event is more likely to be a tidal disruption event (TDE), highly variable AGN, or changing-look (CL) AGN rather than a supernova. From the follow-up observations with GMOS-N and GNIRS, we found that the broad emission lines newly appeared and were highly redshifted, implying that this flare can originate from the TDE accompanied by the CL phenomenon. To further unveil the physical nature of this ongoing MIR-only flare, we propose to obtain multi-epoch optical and NIR spectra. Because TDEs and extremely variable AGNs with significant obscuration are very rare, this observation can provide useful insight into the demography of those species.