High-resolution VLBI observations of and modelling the radio emission from the TDE AT2019dsg

Abstract

A tidal disruption event (TDE) involves the shredding of a star in the proximity of a supermassive black hole (SMBH). The nearby ($\approx$230 Mpc) relatively radio-quiet, thermal emission dominated source AT2019dsg is the first TDE with a potential neutrino association. The origin of non-thermal emission remains inconclusive; possibilities include a relativistic jet or a sub-relativistic 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 $\pm$ 0.65 mas yr${}^{-1}$ ($3.2\pm 2.2c$; $1-\sigma$). Modelling the radio emission favors an origin from the interaction between a decelerating outflow (velocity $\approx$ 0.1 $c$) and a dense circum-nuclear medium. The transition of the synchrotron self-absorption frequency through the observation band marks a peak flux density of 1.19 $\pm$ 0.18 mJy at 152.8 $\pm$ 16.2 days. An equipartition analysis indicates an emission region distance of $⩾$ 4.7 $\times$ 10${}^{16}$ cm, magnetic field strength $⩾$ 0.17 G, and number density $⩾$ 5.7 $\times$ 10${}^3$ cm${}^{-3}$. The disruption involves a $\approx$ 2 $M_{\odot }$ star with a penetration factor $\approx 1$ and a total energy output of $⩽$ 1.5 $\times$ 10${}^{52}$ erg. The outflow is radiatively driven by accretion of stellar debris onto the SMBH. Neutrino production is likely related to the acceleration of protons to PeV energies and the availability of a suitable cross-section at the outflow base. The present study thus helps exclude jet-related origins for non-thermal emission and neutrino production, and constrains non-jetted scenarios.

arXiv comment17 pages, 2 figures, 4 tables. Accepted for publication in The Astrophysical Journal

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