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.