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 ∼GHz radio luminosity of νLνlsim1038 erg s−1 to νLν∼1040 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 nvsim 3000 days with an average 0.1LT⟨beta⟩LT0.6. The jet is energetic (∼1051−52 erg), and had a radius ∼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.