Departament d'Astronomia i Astrofísica
Universitat de València

    Core-shifts and proper-motion constraints in the S5 polar cap sample at the 15 and 43 GHz bands

Fran Abellan

Departament d'Astronomia i Astrofísica, Universitat de València

Seminari del departament d'Astronomia i Astrofísica

Dijous 25 gener 2018



We have studied a complete radio sample of active galactic nuclei (AGN) with the very-long-baseline-interferometry (VLBI) technique and for the first time successfully obtained high precision phase-delay astrometry at Q band (43 GHz) from observations acquired in 2010. We have compared our astrometric results with those obtained with the same technique at U band (15 GHz) from data collected in 2000. The differences in source separations among all the source pairs observed in common at the two epochs are compatible at the 1? level between U and Q bands. With the benefit of quasi-simultaneous U and Q band observations in 2010, we have studied chromatic effects (core-shift) at the radio source cores with three different methods. The magnitudes of the core-shifts are of the same order (about 0.1 mas) for all methods. However, some discrepancies arise in the orientation of the core-shifts determined through the different methods. In some cases these discrepancies are due to insufficient signal for the method used. In others, the discrepancies reflect assumptions of the methods and could be explained by curvatures in the jets and departures from conical jets.