The Wandering Supermassive Black Hole Powering the off-nuclear TDE AT2024tvd

TL;DR

This study models the spectral energy distribution of the off-nuclear TDE AT2024tvd, revealing a wandering supermassive black hole with a high mass ratio, consistent with a tidally stripped galaxy nucleus, using relativistic accretion disk models.

Contribution

It introduces a physically consistent relativistic disk model to analyze TDE SEDs, inferring black hole properties and host galaxy characteristics with improved reliability.

Findings

Black hole mass approximately 10^6 solar masses.

No detectable host galaxy or star cluster down to specified mass limit.

Black hole-to-host mass ratio exceeds 3%, indicating a tidally stripped nucleus.

Abstract

We present an analysis of the spectral energy distribution (SED) of the off-nuclear tidal disruption event (TDE) AT2024tvd during its late-time plateau phase, combining X-ray spectra and UV/optical photometry. Using a fully relativistic, compact accretion disk model with self-consistent inner-disk Comptonization, we reproduce the observed SED without significant residuals. The inferred black hole mass ${\rm log}{10}(M{\bullet}/M_\odot) \approx 6.0 \pm 0.2$, and the inferred disk parameters place AT2024tvd within known TDE-disk scaling relations ($L_{\rm bol}^{\rm disk}/L_{\rm Edd} \propto T_{\rm p}^4 \propto M_{\bullet}^{-1}$, $L_{\rm plat} \propto M_{\bullet}^{2/3}$, $R_{\rm out}/r_{\rm g} \propto M_{\bullet}^{-2/3}$). Our results show that: (i) there is no \textit{detected} star cluster or dwarf galaxy associated with the source, down to a mass limit of $\log_{10}(M_{\rm gal}/M_{\odot}) \leq 7.6$; (ii) the black hole is a wandering supermassive, rather than intermediate-mass, black hole; and (iii) the source represents an extreme case of black hole-to-host mass ratio, with $M_{\bullet}/M_{\rm gal} > 3\%$, consistent with a heavily tidally stripped nucleus. The latter aligns with cosmological simulations predicting that surviving host remnants of most wandering black holes should not retain a detectable stellar overdensity when located at small halo-centric distances. We discuss differences with previous analyses of this source and highlight why our modeling approach provides a more physically consistent solution with more reliable parameter inference.