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

We report the development of a semi-automatic pipeline for the calibration of 86GHz 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 43GHz has not yet been well established. We also present, for the first time, a full-polarization global-VLBI image at 86GHz (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.