A Mildly Relativistic Outflow Launched Two Years after Disruption in Tidal Disruption Event AT2018hyz

Abstract We present late-time radio/millimeter (as well as optical/UV and X-ray) detections of tidal disruption event (TDE) AT2018hyz, spanning 970–1300 d after optical discovery. In conjunction with earlier deeper limits, including those at ?700 days, our observations reveal rapidly rising emission 0.8–240 GHz, steeper than F ? ? t 5 relative to the time Such a steep rise cannot be explained in any reasonable scenario an outflow launched (e.g., off-axis jet, sudden increase ambient density), instead points delayed launch. Our multifrequency data allow us directly determine radius energy radio-emitting outflow, we find from modeling that was ?750 days The velocity is mildly relativistic, ? ? 0.25 ?0.6 for spherical geometry 10° jet geometry, respectively, minimum kinetic E K 5.8 × 10 49 ?6.3 erg, respectively. This first definitive evidence production relativistic TDE; comparison recently published radio light curve ASASSN-15oi suggests final rebrightening observed (at single frequency time) may due similar comparable energy. Finally, note AT2018hyz are intermediate between past nonrelativistic TDEs ASASSN-14li, AT2019dsg) TDE Sw J1644+57. suggest such outflows common TDEs.