Spectroscopic monitoring of the candidate tidal disruption event in F01004-2237

TL;DR

This study reports spectroscopic monitoring of galaxy F01004-2237, revealing spectral changes consistent with a tidal disruption event, but also compatible with AGN activity, thus challenging the interpretation of the flare.

Contribution

It provides long-term spectroscopic data showing spectral evolution that supports the TDE hypothesis while also considering alternative AGN-related explanations.

Findings

Spectral changes align with typical TDE evolution.

Spectral variations are inconsistent with standard AGN reverberation.

Results renew debate on the nature of the observed flare.

Abstract

We present results of spectroscopic monitoring observations of the Ultra-Luminous Infra Red 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 $\lambda$4686 emission and the appearance of He I $\lambda$3898,$\lambda$5876 emission lines. The favoured 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 reason 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 observed from reverberation mapping studies of AGNs, renewing the discussion on the interpretation of the flare as a TDE.