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The first-known tidal disruption event (TDE) with strong evidence for arelativistic jet -- based on extensive multi-wavelength campaigns -- is SwiftJ1644+5734. In order to directly measure the apparent speed of the radio jet,we performed very long baseline interferometry (VLBI) observations with theEuropean VLBI network (EVN) at 5 GHz. Our observing strategy was to identify avery nearby and compact radio source with the real-time e-EVN, and then utilisethis source as a stationary astrometry reference point in the later five deepEVN observations. With respect to the in-beam source FIRST J1644+5736, we haveachieved a statistical astrometric precision about 12 micro-arcsecond (68 %confidence level) per epoch. This is one of the best phase-referencingmeasurements available to date. No proper motion has been detected in the SwiftJ1644+5734 radio ejecta. We conclude that the apparent average ejection speedbetween 2012.2 and 2015.2 was less than 0.3c with a confidence level of 99 %.This tight limit is direct observational evidence for either a very smallviewing angle or a strong jet deceleration due to interactions with a densecircum-nuclear medium, in agreement with some recent theoretical studies.

No apparent superluminal motion in the first-known jetted tidal disruption event Swift J1644+5734