Polarization VLBI at 22 and 43~GHz

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Session 75 -- VLBI Obsesrvations
Display presentation, Friday, January 14, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[75.01] Polarization VLBI at 22 and 43~GHz

K.~J.~Lepp\"anen, J.~A.~Zensus, P.~J.~Diamond (NRAO)

We discuss a new technique for imaging the radio polarization structure of extragalactic objects at unprecedented angular resolution using Very Long Baseline Interferometry (VLBI). The technique is under development and employs observing frequencies of 22 and 43~GHz yielding an improvement in resolution by an order of magnitude with respect to observations up to date. It relies on the use of strong water/SiO-maser line calibrator sources to overcome the difficulties of conventional calibration schemes, which have so far limited continuum polarization VLBI observations to much lower frequencies---usually 5~GHz. The high signal to noise ratio and the relatively simple structure of these sources (small number of point-like components) on a single frequency channel allow accurate calibration of the feed polarization parameters, essential for imaging the weak cross polarized continuum emission from the program source. Some maser components exhibit strong linear polarization, making it easier to maintain phase coherence between the two orthogonally polarized observing channels, and possibly enabling the determination of the true E-vector position angle. This technique will be established for the reduction of high frequency polarization data from the Very Long Baseline Array within the Astronomical Image Processing System (AIPS).

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