5 Conclusions

We have made VLBA observations of the quasar 3C395 at 8.4 and 15.4 in 1995.91, and at 15.4 and 22.2 in 1998.50, and have obtained detailed maps of its parsec-scale jet, in total intensity and in polarization. The one-sided jet is complex, showing the previously reported gross structure of three components, A, B and C, but with remarkable sub-structure when observed at sub-milliarcsecond angular resolution. The emission of 3C395 is strongly dominated by component A. The new data confirm the stationary character of component B, also in polarized emission. Component C appears very elongated at 8.4 GHz, being more likely the result of the underlying jet emission. It is resolved out at higher frequencies.

We have studied the sub-structure within component A, i.e. the core and the inner jet region (of $\sim$3 mas length), which is crucial to understand the relation between flux density and structural variability in 3C395. We have found clear structural variations in the inner jet, with a new component ejected from the core. In polarization, we have observed also important time and frequency dependent variations of the inner jet structure, most possibly associated with the ejection of a new component from the core. The variability of this region of 3C395 contrasts with the apparent stability inferred from lower angular resolution observations, which could only determine that total flux density variability was due to activity within component A.

The observations show that the jet of 3C395 has a projected magnetic field essentially aligned with the direction of the jet, indicating that this parallel field is stronger than the field compression exerted by the shock wave associated with the new ejected component. The underlying parallel magnetic field is strong enough to be detected at a distance of 16 mas ($\sim$60 pc) from the core. We find good agreement when comparing the degree of polarization and the electric vector position angle obtained from our VLBA data (Table 2) and from close-in-time single dish data (database of the University of Michigan Radio Astronomy Observatory: EVPA 33$^{\circ}$ and polarization degree of 3% at 15 GHz in epoch 1998.37), indicating that the polarization of the source as a whole is mainly associated with the compact radio source and, in particular, components A and B.

Finally, we estimate a high Faraday RM, $\sim$+2500 rad m^-2, close to the core region, and a strong gradient along the inner jet, reaching RM $\sim$-350 rad m^-2 at a distance of only 2 - 3 mas from the core. These values are in agreement with the results derived by Taylor (2000).

Follow up observations of moving components such as A2 in the inner jet of 3C395 at high angular resolution, by means of high frequency and/or space-VLBI observations, would eventually allow us to trace the jet curvature close to the core before those components fade away below the noise level as they reach the sharp cut in the emission profile beyond component A. We guess that only very strong components would be detected in the region between components A and B, probably similar to the one observed during the 1980's (Waak et al. 1985).

Acknowledgements

We thank Kari Leppänen for his invaluable help during the 1995 data reduction process and the referee for helpful and constructive comments to the paper. A. A. acknowledges the European Commission's TMR Programme, Access to Large Scale Facilities, under contract No. ERBFMGECT950012 for providing financial support to visit the Joint Institute for VLBI in Europe (JIVE) for data reduction. This research is supported in part by the Spanish DGES Grant (PB97-1164) and has made use of data from the University of Michigan Radio Astronomy Observatory which is supported by funds from the University of Michigan. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.