Continued Rapid Radio Brightening of the Tidal Disruption Event AT2018hyz

Abstract We present ongoing radio observations of the tidal disruption event (TDE) AT2018hyz, which was first detected in the radio at 972 days after disruption, following multiple nondetections from earlier searches. The new observations presented here span ≈1370–2160 days and 0.88–240 GHz. We find that the light curves continue to rise at all frequencies during this time period, following a power law of about F ν ∝ t 3 (compared to F ν ∝ t 5.7 at 972–1400 days) and reaching a peak luminosity of L ≈ 10 40 erg s −1 , comparable to the luminosity of the relativistic TDE Sw 1644+57 on the same timescale. The multifrequency data indicate that the peak frequency does not significantly evolve over the 1030 days span of our observations, while the peak flux density increases by an order of magnitude. The observed behavior is consistent with two possible scenarios: (i) a delayed spherical outflow launched about 620 days postdisruption with a velocity of ≈0.3 c and an energy of ∼10 50 erg; or (ii) a highly off-axis (≈80°–90°) relativistic jet with a Lorentz factor of Γ ∼ 8 and E K ≈ 10 52 erg. Continued radio observations to capture the light-curve peak, as well as very long baseline interferometry observations, could distinguish between these scenarios.