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Cross-polarization gain calibration of linearly polarized VLBI antennas by observations of 4C 39.25
  • +12
  • Frédéric Jaron,
  • I Martí-Vidal,
  • M Schartner,
  • J González-García,
  • E Albentosa-Ruiz,
  • S Bernhart,
  • J Böhm,
  • J Gruber,
  • S Modiri,
  • A Nothnagel,
  • V Pérez-Díez,
  • T Savolainen,
  • B Soja,
  • E Varenius,
  • M H Xu
Frédéric Jaron
Max-Planck-Institut für Radioastronomie, Technische Universität Wien

Corresponding Author:[email protected]

Author Profile
I Martí-Vidal
Observatori Astronòmic, Universitat de València, Departament d'Astronomia i Astrofìsica, Universitat de València
M Schartner
Institute of Geodesy and Photogrammetry, ETH Zürich
J González-García
Centro Astronómico de Yebes (IGN)
E Albentosa-Ruiz
Observatori Astronòmic, Universitat de València
S Bernhart
Federal Agency for Cartography and Geodesy (BKG), Department Geodesy, Reichert GmbH, Max-Planck-Institut für Radioastronomie
J Böhm
Technische Universität Wien
J Gruber
Technische Universität Wien
S Modiri
Federal Agency for Cartography and Geodesy (BKG), Department Geodesy
A Nothnagel
Technische Universität Wien
V Pérez-Díez
OAN-IGN), Observatorio Astronómico Nacional, Centro Astronómico de Yebes (IGN)
T Savolainen
Department of Electronics and Nanoengineering, Aalto University, Aalto University Metsähovi Radio Observatory, Max-Planck-Institut für Radioastronomie
B Soja
Institute of Geodesy and Photogrammetry, ETH Zürich
E Varenius
Chalmers University of Technology
M H Xu
GFZ German Research Centre for Geosciences, Aalto University Metsähovi Radio Observatory


Radio telescopes with dual linearly polarized feeds regularly participate in Very Long Baseline Interferometry (VLBI). One example is the VLBI Global Observing System (VGOS), which is employed for high-precision geodesy and astrometry. In order to achieve the maximum signal-to-noise ratio, the visibilities of all four polarization products are combined to Stokes I before fringe-fitting. Our aim is to improve cross-polarization bandpass calibration, which is an essential processing step in this context. Here we investigate the shapes of these station-specific quantities as a function of frequency and time. We observed the extra-galactic source 4C 39.25 for six hours with a VGOS network. We correlated the data with the DiFX software and analyzed the visibilities with PolConvert to determine the complex cross-bandpasses with high accuracy. Their frequency-dependent shape is to first order characterized by a group delay between the two orthogonal polarizations, in the order of several hundred picoseconds. We find that this group delay shows systematic variability in the range of a few picoseconds, but can remain stable within this range for several years, as evident from earlier sessions. On top of the linear phase-frequency relationship there are systematic deviations of several tens of degrees, which in addition are subject to smooth temporal evolution. The antenna cross-bandpasses are variable on time scales of ∼ 1 hour, which defines the frequency of necessary calibrator scans. The source 4C 39.25 is confirmed as an excellent cross-bandpass calibrator. Dedicated surveys are highly encouraged to search for more calibrators of similar quality.
01 Mar 2024Submitted to ESS Open Archive
04 Mar 2024Published in ESS Open Archive