http://arxiv.org/abs/1510.01226
The tidal disruption of stars by supermassive black holes (SMBH) lights up dormant systems and can be used to probe accretion and outflow processes. Theoretical calculations indicate that most tidal disruption events (TDEs) lead to super-Eddington accretion, which in turn drives outflows. The discovery of luminous radio emission from the $\gamma$-ray TDE Sw J1644+57 revealed the formation of a relativistic jetted outflow, but such events represent $\lesssim 1\%$ of the TDE population. Direct evidence for outflows in the bulk of the TDE population, discovered through optical, ultraviolet (UV), and X-ray observations, has been lacking. Here we report the discovery of transient radio emission from the nearby optically-discovered TDE ASASSN-14li (distance of 90 Mpc), making it the first normal TDE detected in the radio, and unambiguously pointing to the formation of a non-relativistic outflow with a kinetic energy of $\approx 10^{48}$ erg, a velocity of $\approx 12,000-39,000$ km s$^{-1}$, and a mass of $\approx 10^{-4}-10^{-3}$ M$_{\odot}$. 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, $\rho(R)\propto R^{-2.6}$ 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 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.
K. Alexander, E. Berger, J. Guillochon, et. al.
Tue, 6 Oct 15
22/78
Comments: 5 figures, 2 tables
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