4C 39.25: Multi-epoch polarisation observations at 15, 22 and 43 GHz

We present multi-epoch simultaneous 15, 22 and 43 GHz VLBA polarimetric radio observations of the quasar 4C 39.25 which provide further evidence for the ongoing interaction between components 'a' and 'b' through the monitoring of the total and polarised flux densities of both components, the proper motion of 'b' and, more importantly, of the polarisation angle associated with components 'a' and 'b'. There are strong pieces of evidence indicating that the superluminal component 'b' is 'colliding' or 'crossing' the region associated with the stationary component 'a': (i) at millimeter wavelengths, the total flux density of 4C 39.25 has reached a maximum and is already beginning to decline; (ii) at centimeter wavelengths, the total flux density light curve has reached a 'plateau' at its maximum value while the polarised flux density is already decreasing; and (iii) the proper motion of 4C 39.25 with respect to the quasi-inertial reference frame defined by the sources observed in the USNO-programme shows a sharp change in the slope during 1997-1998.