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

TL;DR

AT2024tvd investigates an off-nuclear TDE around a wandering SMBH with no detectable nearby host. The authors perform full SED fitting using a color-corrected relativistic accretion-disk model with self-consistent inner-disk Comptonization (kerrSED with SimPL) on two epochs of X-ray and UV/optical data within a Bayesian framework. They find $M_{bh} ≈ 10^6 M_sun$ (i.e., log10$(M_{bh}/M_sun) ≈ 6.0 ± 0.2$) and disk scalings that match known TDE-disk relations, with no detected stellar overdensity down to log10$(M_{gal}/M_sun) ≤ 7.6$ indicating $M_{bh}/M_{gal} > 3 ext{%}$. The results support a physically consistent disk+corona interpretation and demonstrate improved parameter inference over previous analyses, aligning with simulations predicting undetectable overdensities for remnants at small halo-centric distances.

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.

Figures (2)

• Figure 1: Left: diffraction limit RGB image of AT2024tvd using HST+JWST imaging. Right: multi-wavelength light curves of AT2024tvd, with the orange marker shewing the epochs in which our SED fitting was performed. For plotting purposes the UVOT light curves were binned to have no more than one point each five days.
• Figure 2: Spectral energy distribution modeling of AT2024tvd. The upper panels show the emission in the observer frame, while the lower panels display the rest-frame emission corrected for all absorption and extinction/attenuation effects. The left column presents the early-time, disk-dominated XMM-Newton spectrum, which is well reproduced within an inner accretion disk plus corona framework. At later times, the full optical/UV–X-ray SED is consistently reproduced using the same disk framework (right column). The dashed lines indicate the median disk solutions with the coronal component turned off.