Quasar 4C39.25 is not contracting

Abstract

The milli-arc second radio structure of the quasar 4C39.25 has previously been described as consisting of two components whose angular separation remained constant at ˜2 marc s, whereas their relative flux densities varied with time^1–3. This behaviour is in marked contrast to other similar sources whose radio structures expand superluminally⁴. Recently, Shaffer⁵ suggested that 4C39. 25 may have been contracting superluminally in the period 1979–82. Here, based on our map of this source made from VLBI observations in 1983 at λ3.6 cm, we conclude that this conjecture is not correct. We find three distinct components in the structure, two of which are separated by 2.0 marc s, whereas the third, presumably new and not previously reported, is situated between the other two. It is possible either that the third component is stationary and that its flux density has rapidly increased to render it visible, or that it has recently been ejected from the westernmost component.