2008A&A...478..267M

We report on the first wide-field, high-precision astrometric analysis of the 13 extragalactic radio sources of the complete S5 polar cap sample at 15.4GHz. We describe new algorithms developed to enable the use of differenced phase delays in wide-field astrometric observations and discuss the impact of using differenced phase delays on the precision of the wide-field astrometric analysis. From this global fit, we obtained estimates of the relative source positions with precisions ranging from 14 to 200µas at 15.4GHz, depending on the angular separation of the sources (from ∼1.6 to ∼20.8degrees). These precisions are ∼10 times higher than the achievable precisions using the phase-reference mapping technique.