Inverse Multview I: Multi-Calibrator inverse phase referencing for Microarcsecond VLBI Astrometry

TL;DR

This paper introduces an extension of the Multiview VLBI calibration method, called inverse Multiview, which significantly improves astrometric accuracy at lower frequencies by better modeling ionospheric delays.

Contribution

The paper presents the inverse Multiview technique, enhancing VLBI calibration by phase referencing to the target, achieving near 20 microarcsecond accuracy at 8.3 GHz.

Findings

Achieved ~20 μas astrometric accuracy in single-epoch observations.

Improved accuracy by up to an order of magnitude over standard phase referencing.

Effective for target-reference separations up to 7 degrees.

Abstract

Very Long Baseline Interferometry (VLBI) astrometry is a well established technique for achieving $\pm10~\mu$as parallax accuracies at frequencies well above 10~GHz. At lower frequencies, uncompensated interferometer delays associated with the ionosphere play the dominant role in limiting the astrometric accuracy. Multiview is a novel VLBI calibration method, which uses observations of multiple quasars to accurately model and remove time-variable, directional-dependent changes to the interferometer delay. Here we extend the Multiview technique by phase referencing data to the target source ("inverse Multiview") and test its performance. Multiple observations with a four-antenna VLBI array operating at 8.3~GHz show single-epoch astrometric accuracies near $20~\mu$as for target-reference quasar separations up to about 7 degrees. This represents an improvement in astrometric accuracy by up to an order of magnitude compared to standard phase referencing.