Towards an astronomical use of new-generation geodetic observations

I. From the correlator to full-polarization images

¹ Observatorio Astronómico Nacional (OAN-IGN), Alfonso XII 3, 28014 Madrid, Spain
e-mail: v.perez@oan.es
² Dpt. Astronomia i Astrofísica, Universitat de València, C/ Dr. Moliner 50, 46120 Burjassot, Spain
³ Observatori Astronòmic, Universitat de València, C/ Cat. José Beltrán 2, 46980 Paterna, Spain
⁴ Centro de Desarrollos Tecnológicos, Observatorio de Yebes (IGN), 19141 Yebes, Guadalajara, Spain
⁵ Technische Universität Wien, Wiedner Hauptstraße 8–10, 1040 Wien, Austria
⁶ Aalto University Metsähovi Radio Observatory, Metsähovintie 114, 02540 Kylmälä, Finland
⁷ Aalto University Department of Electronics and Nanoengineering, PO Box 15500, 00076 Aalto, Finland
⁸ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁹ GFZ German Research Centre for Geosciences, 14473 Potsdam, Germany

Received: 16 November 2023
Accepted: 3 June 2024

Abstract

Context. The current algorithms used for the calibration and analysis of very long baseline interferometry (VLBI) networks that only use linear polarizers (as is the case of the VLBI Global Observing System, VGOS) do not properly account for instrumental and source-intrinsic polarimetry, which can cause errors in geodetic and astronomical products.

Aims. We aim to develop a calibration pipeline for VLBI interferometers that observe in a basis of linear polarization, as is the case of VGOS. The products from this pipeline can be used to obtain valuable full-polarization astronomical information from the observed sources, and they can be used to potentially improve the geodetic results.

Methods. We used the algorithm PolConvert to write the correlation products in a basis of circular polarization that is compatible with the standard VLBI calibration procedures. In addition to this, we implemented a wide-band global fringe-fitting algorithm that accounts for dispersive effects (ionospheric delay) and allows us to perform full-polarization imaging of all the observed sources, covering the whole frequency band of VGOS.

Results. We present the outcome of our pipeline applied to a global IVS VGOS epoch of observations and show example imaging results in total intensity and polarization. We also discuss issues encountered during the analysis and suggest points of improvement in the VGOS system for an optimum geodetic and astronomical exploitation of this interferometer.