Discovery of an Outflow from Radio Observations of the Tidal Disruption event ASASSN-14li

Abstract

We report the discovery of transient radio emission from the nearby optically-discovered TDE ASASSN-14li (distance of 90 Mpc), making it the first typical TDE detected in the radio, and unambiguously pointing to the formation of a non-relativistic outflow with a kinetic energy of ≈ 4−10×1047 erg, a velocity of ≈ 12, 000 − 36, 000 km s−1 , and a mass of ≈ 3 × 10−5 − 7 × 10−4 M⊙. We show that the outflow was ejected on 2014 August 11–25, in agreement with an independent estimate of the timing of super-Eddington accretion based on the optical, UV, and X-ray observations, and that the ejected mass corresponds to about 1 − 10% of the mass accreted in the super-Eddington phase. The temporal evolution of the radio emission also uncovers the circumnuclear density profile, ρ(R) ∝ R−2.5 on a scale of about 0.01 pc, a scale that cannot be probed via direct measurements even in the nearest SMBHs. Our discovery of radio emission from the nearest well-studied TDE to date, with a radio luminosity lower than all previous limits, indicates that non-relativistic outflows are ubiquitous in TDEs, and that future, more sensitive, radio surveys will uncover similar events.