Physics of the central region in the quasar 0850+581
  The apparent position of the origin (core) of extragalactic radio jets shifts with the observing frequency, owing to synchrotron self-absorption and external absorption. One of the largest core shifts was detected by us in the quasar 0850+581 between 2 and 8 GHz. We have followed this up recently by a dedicated VLBA experiment at 5, 8, 15, 24, and 43 GHz. First results from this study enabled estimating the absolute geometry and physical conditions in the parsec-scale jet origin. 
Y. Y. Kovalev (MPIfR and ASC Lebedev), A. P. Lobanov (MPIfR), A. B.   Pushkarev (MPIfR, CrAO, Pulkovo)