High-resolution VLBI Observations of and Modeling the Radio Emission from the Tidal Disruption Event AT2019dsg

Abstract

Abstract A tidal disruption event (TDE) involves the shredding of a star in the proximity of a supermassive black hole (SMBH). The nearby (≈230 Mpc) relatively radio-quiet, thermal-emission-dominated source AT2019dsg is the first TDE with a potential neutrino association. The origin of nonthermal emission remains inconclusive; possibilities include a relativistic jet or a subrelativistic outflow. Distinguishing between them can address neutrino production mechanisms. High-resolution very long baseline interferometry 5 GHz observations provide a proper motion of 0.94 ± 0.65 mas yr−1 (3.2 ± 2.2 c; 1σ). Modeling the radio emission favors an origin from the interaction between a decelerating outflow (velocity ≈0.1 c) and a dense circumnuclear medium. The transition of the synchrotron self-absorption frequency through the observation band marks a peak flux density of 1.19 ± 0.18 mJy at 152.8 ± 16.2 days. An equipartition analysis indicates an emission-region distance of ≥ 4.7 × 1016 cm, magnetic field strength ≥ 0.17 G, and number density ≥ 5.7 × 103 cm−3. The disruption involves a ≈2 M ⊙ star with a penetration factor ≈1 and a total energy output of ≤ 1.5 × 1052 erg. The outflow is radiatively driven by the accretion of stellar debris onto the SMBH. Neutrino production is likely related to the acceleration of protons to peta-electron-volt energies and the availability of a suitable cross section at the outflow base. The present study thus helps exclude jet-related origins for nonthermal emission and neutrino production, and constrains nonjetted scenarios.