Discovery of a Mid-infrared Echo from the TDE candidate in the nucleus of ULIRG F01004-2237

We present the mid-infrared light curves (LC) of a tidal disruption event (TDE) candidate in the center of a nearby ultraluminous infrared galaxy (ULIRG) F01004-2237 using archival WISE and NEOWISE data with time span of 2010 to 2016. At the peak of the optical flare, F01004-2237 is IR quiescent. About 3 years later, its mid-IR fluxes show steady increase, rising by 1.34 and 1.04 magnitude in 3.4 and 4.6 {\mu}m up to the end of 2016. The host subtracted mid-IR peak luminosity is $2-3\times10^{44} erg s^{-1}$. We interpret the mid-IR LCs as an infrared echo, i.e. dust reprocessed emission of the optical flare. Fitting the mid-IR LCs using our dust model, we infer a dust torus of size a few parsecs at some inclined angle. The derived dust temperatures range from $590-850$ K, and warm dust mass ~7 Msun. Our dust model also explains the long tail of the optical flare as scattered light. The bolometric luminosity is $4-11\times10^{44} erg s^{-1}$, implying a total energy of $1-4\times10^{52}$ erg, suggesting a large dust covering factor.

Comments: submitted to ApJL

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