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We have analyzed archival VLBA data for Cygnus A between 2002 and 2013, tosearch for radio emission from the transient discovered in 2015 by\citet{per18} approximately 0.4\arcsec~ from the nucleus of Cygnus A (Cyg A-2).\citet{per18} use VLA and VLBA archival data (between 1989 and 1997) to showthat the transient rises in flux density by a factor of at least five in lessthan approximately 20 years. With the additional data presented here, we revisethe rise time to between approximately four years and six years, based on a newdetection of the source at 15.4 GHz from October 2011. Our results strengthenthe interpretation of Cyg A-2 as the result of a Tidal Disruption Event (TDE),as we can identify the location of the compact object responsible for the TDEand can estimate the angular expansion speed of the resulting radio emittingstructures, equivalent to an apparent expansion speed of $<0.9c$. While ourresults are consistent with recent X-ray analyses, we can rule out a previouslysuggested date of early 2013 for the timing of the TDE. We favour a timingbetween early 2009 and late 2011. Applying the model of \citet{nak11}, wesuggest a TDE causing a mildly relativistic outflow with a (density-dependent)total energy $>10^{49}$ erg. Due to the improved temporal coverage of ourarchival measurements, we find that it is unlikely that Cyg A-2 has previouslybeen in a high luminosity radio state over the last 30 years.

Archival VLBA observations of the Cygnus A Nuclear Radio Transient (Cyg A-2) Strengthen the Tidal Disruption Event Interpretation