The WISE Detection of an Infrared Echo in Tidal Disruption Event ASASSN-14li

TL;DR

This paper reports the first confirmed detection of infrared dust echoes in a tidal disruption event, ASASSN-14li, revealing dust heating and re-emission consistent with the event's luminosity.

Contribution

It provides the first observational evidence of infrared echoes from dust in a TDE, linking infrared variability to the event's peak luminosity and dust sublimation.

Findings

Infrared flux increased by 0.12 and 0.16 magnitudes in W1 and W2 bands.

Infrared emission persisted for over 170 days after initial detection.

Dust temperature estimated at ~2100 K, near sublimation temperature.

Abstract

We report the detection of a significant infrared variability of the nearest tidal disruption event (TDE) ASASSN-14li using Wide-field Infrared Survey Explorer} and newly released Near-Earth Object WISE Reactivation} data. In comparison with the quiescent state, the infrared flux is brightened by 0.12 and 0.16 magnitude in the W1 ($3.4\mu$m) and W2 ($4.6\mu$m) bands at 36 days after the optical discovery (or $\sim110$ days after the peak disruption date). The flux excess is still detectable $\sim170$ more days later. Assuming that the flare-like infrared emission is from the dust around the black hole, its blackbody temperature is estimated to be $\sim2.1\times10^3$~K, slightly higher than the dust sublimation temperature, indicating that the dust is likely located close to the dust sublimation radius. The equilibrium between the heating and radiation of the dust claims a bolometric luminosity of $\sim10^{43}-10^{45}$~\lum, comparable with the observed peak luminosity. This result has for the first time confirmed the detection of infrared emission from the dust echoes of TDEs.