On the calibration of full-polarization 86 GHz global VLBI observations

I. Martí-Vidal^1,2, T. P. Krichbaum¹, A. Marscher³, W. Alef¹, A. Bertarini^1,4, U. Bach¹, F. K. Schinzel^1⋆, H. Rottmann¹, J. M. Anderson¹, J. A. Zensus¹, M. Bremer⁵, S. Sanchez⁶, M. Lindqvist² and A. Mujunen⁷

¹ Max-Planck-Institut für Radioastronomie (MPIfR), Auf dem Hügel 69, 53121 Bonn, Germany
² Onsala Space Observatory, Chalmers University of Technology, Observatorievägen 90, 43992 Onsala, Sweden
e-mail: ivan.marti-vidal@chalmers.se
³ Institute for Astrophysical Research, Boston University, 725 Commonwealth Avenue, Boston, MA-02215, USA
⁴ Institute of Geodesy and Geoinformation, Bonn University, Nussallee 17, 53115 Bonn, Germany
⁵ Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, 38406 Saint Martin d’ Hères, France
⁶ Instituto de Radioastronomía Milimétrica (IRAM), Av. Divina Pastora 7, Núcleo Central, 18012 Granada, Spain
⁷ Metsähovi Radio Observatory (Aalto University), Metsähovintie 114, 02540 Kylmälä, Finland

Received: 3 February 2012
Accepted: 7 March 2012

Abstract

We report the development of a semi-automatic pipeline for the calibration of 86 GHz full-polarization observations performed with the Global Millimeter-VLBI array (GMVA) and describe the calibration strategy followed in the data reduction. Our calibration pipeline involves non-standard procedures, since VLBI polarimetry at frequencies above 43 GHz has not yet been well established. We also present, for the first time, a full-polarization global-VLBI image at 86 GHz (source 3C 345), as an example of the final product of our calibration pipeline, and discuss the effect of instrumental limitations on the fidelity of the polarization images. Our calibration strategy is not exclusive to the GMVA, and could be applied to other VLBI arrays at millimeter wavelengths. The use of this pipeline will allow GMVA observers to obtain fully calibrated datasets shortly after the data correlation.