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arXiv · 1605.06461

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

J. Yang·Z. Paragi·A. J. van der Horst·L. I. Gurvits·R. M. Campbell·D. Giannios·T. An·S. Komossa
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Abstract

The first-known tidal disruption event (TDE) with strong evidence for a relativistic jet -- based on extensive multi-wavelength campaigns -- is Swift J1644+5734. In order to directly measure the apparent speed of the radio jet, we performed very long baseline interferometry (VLBI) observations with the European VLBI network (EVN) at 5 GHz. Our observing strategy was to identify a very nearby and compact radio source with the real-time e-EVN, and then utilise this source as a stationary astrometry reference point in the later five deep EVN observations. With respect to the in-beam source FIRST J1644+5736, we have achieved a statistical astrometric precision about 12 micro-arcsecond (68 % confidence level) per epoch. This is one of the best phase-referencing measurements available to date. No proper motion has been detected in the Swift J1644+5734 radio ejecta. We conclude that the apparent average ejection speed between 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 small viewing angle or a strong jet deceleration due to interactions with a dense circum-nuclear medium, in agreement with some recent theoretical studies.

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J. Yang, Z. Paragi, A. J. van der Horst, L. I. Gurvits, R. M. Campbell, D. Giannios, T. An, S. Komossa. 2016-05-23. No apparent superluminal motion in the first-known jetted tidal disruption event Swift J1644+5734. https://doi.org/10.1093/mnrasl%2Fslw107

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