paper

Infrared Echoes of Optical Tidal Disruption Events: ~1% Dust Covering Factor or Less at sub-parsec Scale

arXiv:2102.08044 · doi:10.3847/1538-4357/abe772

Abstract

The past decade has experienced an explosive increase of optically-discovered tidal disruption events (TDEs) with the advent of modern time-domain surveys. However, we still lack a comprehensive observational view of their infrared (IR) echoes in spite of individual detections. To this end, we have conducted a statistical study of IR variability of the 23 optical TDEs discovered between 2009 and 2018 utilizing the full public dataset of Wide-field Infrared Survey Explorer. The detection of variability is performed on the difference images, yielding out 11 objects with significant (>) variability in at least one band while dust emission can be only fitted in 8 objects. Their peak dust luminosity is around - erg/s, corresponding to a dust covering factor at scale of sub-parsec. The only exception is the disputed source ASASSN-15lh, which shows an ultra-high dust luminosity ( erg/s) and make its nature even elusive. Other non-detected objects show even lower , which could be one more order of magnitude lower. The derived is generally much smaller than those of dusty tori in active galactic nuclei (AGNs), suggesting either a dearth of dust or a geometrically thin and flat disk in the vicinity of SMBHs. Our results also indicate that the optical TDE sample (post-starburst galaxies overrepresented) is seriously biased to events with little dust at sub-pc scale while TDEs in dusty star-forming systems could be more efficiently unveiled by IR echoes.

ApJ accepted, 5 figures, 3 tables

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