On the Calibration of Full-polarization 86GHz Global VLBI Observations

TL;DR

This paper introduces a semi-automatic calibration pipeline for 86 GHz full-polarization VLBI observations, enabling improved data quality and polarization imaging at millimeter wavelengths, exemplified by the first full-polarization image of 3C 345.

Contribution

The paper presents a novel calibration pipeline for 86 GHz VLBI polarimetry, including non-standard procedures and a demonstration with the first full-polarization image at this frequency.

Findings

First full-polarization 86 GHz VLBI image of 3C 345.

Calibration pipeline reduces instrumental effects and improves image fidelity.

Pipeline is adaptable to other millimeter VLBI arrays.

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 is not yet 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 for the GMVA, and could be applied on other VLBI arrays at millimeter wavelengths. The use of this pipeline will allow GMVA observers to get fully-calibrated datasets shortly after the data correlation.