A candidate relativistic tidal disruption event at 340 Mpc

Abstract

We present observations of an extreme radio flare, VT J024345.70-284040.08, hereafter VT J0243, from the nucleus of a galaxy with evidence for historic Seyfert activity at redshift $z=0.074$. Between NRAO VLA Sky Survey observations in 1993 to VLA Sky Survey observations in 2018, VT J0243 rose from a $\sim$GHz radio luminosity of $\hat{I}½L_{\hat{I}}½\lesssim 10^{38}$ erg s${}^{-1}$ to $\hat{I}½L_{\hat{I}}½\sim 10^{40}$ erg s${}^{-1}$, and still continues to brighten. The radio spectral energy distribution (SED) evolution is consistent with a nascent jet that has slowed over $\sim 3000$ days with an average $0.1<⟨{\hat{I}}^2⟩<0.6$. The jet is energetic ($\sim 10^{51-52}$ erg), and had a radius $\sim 0.7$ pc in Dec. 2021. X-ray observations suggest a persistent or evolving corona, possibly associated with an accretion disk, and IR and optical observations constrain any high-energy counterpart to be sub-Eddington. VT J0243 may be an example of a young, off-axis radio jet from a slowly evolving tidal disruption event. Other more mysterious triggers for the accretion enhancement and jet launching are possible. In either case, VT J0243 is a unique example of a nascent jet, highlighting the unknown connection between supermassive black holes, the properties of their accretion flows, and jet launching.

20 pages, 5 figures, 3 tables. Submitted to ApJ