Verification of the Polarimetric Capability of the East Asia VLBI Network

TL;DR

This paper systematically verifies the polarimetric performance of the East Asia VLBI Network at 22 and 43 GHz, demonstrating its calibration stability and imaging capabilities comparable to VLBA, thus supporting future high-fidelity polarimetric studies.

Contribution

First comprehensive assessment of EAVN's polarimetric performance, including calibration stability, phase correction methods, and comparison with VLBA results at high frequencies.

Findings

EAVN shows stable polarimetric leakages of 5-10% over months.

Phase stability is restored after applying analytically derived FR corrections.

EAVN's polarization results broadly agree with VLBA within uncertainties.

Abstract

The East Asia VLBI Network (EAVN) has recently enabled dual-polarization observations at $22$ and $43\,\mathrm{GHz}$. We present the first systematic verification of its polarimetric performance using EAVN observations of M87, 3C 279, 3C 273, and OJ 287, calibrated with the GPCAL pipeline and evaluated against near-contemporaneous VLBA images at comparable frequencies. Most stations show stable polarimetric leakages with amplitudes of $5$-$10\%$ over monthly timescales. While several VERA stations exhibit D-term phase variations between epochs, we attribute these to field-rotator (FR) offsets and demonstrate that phase stability is restored after applying the analytically derived FR corrections. The resulting linear-polarization morphologies and EVPAs broadly agree with the VLBA results within uncertainties; fractional polarization measured by the EAVN tends to be slightly higher near polarization peaks. Although exact one-to-one comparisons are limited by moderate frequency and epoch differences, the combined evidence indicates robust EAVN polarimetric calibration and imaging capabilities at $22$ and $43\,\mathrm{GHz}$. These results support the scientific capability of EAVN polarimetry and lay the groundwork for expanded, higher-fidelity polarimetric studies in East Asia.