A Candidate Relativistic Tidal Disruption Event at 340 Mpc

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 Very Large Array (VLA) Sky Survey observations in 1993 to VLA Sky Survey observations in 2018, VT J0243 rose from a ~ GHz radio luminosity of ν L _ν ≲ 10³⁸ erg s^-1 to ν L _ν ~ 10⁴⁰ erg s^-1, and still continues to brighten. The radio spectral energy distribution evolution is consistent with a nascent jet that has slowed over ~3000 days with an average 0.1 <<β>< 0.6. The jet is energetic (~10^51-52 erg), and had a radius ~0.7 pc in 2021 December. 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.