Abstract
Abstract We present results of spectroscopic monitoring observations of the ultraluminous infrared galaxy F01004−2237. This galaxy was observed to undergo changes in its optical spectrum, detected by comparing a spectrum from 2015 with one from 2000. These changes were coincident with photometric brightening. The main changes detected in the optical spectrum are enhanced He ii λ4686 emission and the appearance of He i λ3898,λ5876 emission lines. The favored interpretation of these changes was that of a tidal disruption event (TDE) happening in 2010. However, subsequent work suggested that these changes are caused by another hitherto unknown effect related to variations in the accretion rate in the active galactic nucleus (AGN). Our optical spectroscopic monitoring observations show that the evolution of the He lines is in line with the evolution seen in TDEs and opposite of what is observed from reverberation-mapping studies of AGNs, renewing the discussion of the interpretation of the flare as a TDE.
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