A New Method for Cross Polarized Delay Calibration of Radio Interferometers

TL;DR

This paper introduces a novel calibration technique for correcting instrumental delays in cross-polarized radio interferometry data, enhancing the accuracy of polarization measurements in radio astronomy.

Contribution

It presents a new method for cross-polarized delay calibration and demonstrates its application within the Obit software package using EVLA data.

Findings

Successfully calibrated EVLA data with the new method

Effective in both strongly and weakly polarized calibrator observations

Improves polarization measurement accuracy

Abstract

Radio interferometers can measure the full polarization state of incoming waves by cross--correlating all combinations of two orthogonal polarizations at each antenna. The independent sets of electronics used to detect the two polarization states will introduce a differential instrumental delay between the two data streams. The usual technique of separate calibration of the parallel--hand sets of visibilities still allows for an arbitrary offset in group delay and phase between the two parallel systems. In order to use the cross--polarized visibilities, this instrumental offset must be determined and removed. This paper describes one such technique and explores its application in the Obit package. The technique is successfully applied to some EVLA data using both strongly and weakly polarized calibrators.