Solving for closure errors due to polarization leakage in radio interferometry of unpolarized sources

Abstract

Mechanical and electronic imperfections can result into polarization leakage in individual antennas of a radio interferometer. Such leakages manifest themselves as closure errors even in co-polar visibility measurements of unpolarized sources. This paper describes and tests a method for the study of polarization leakage for radio interferometric telescopes using only the nominally co-polar visibilities for unpolarized calibrators. Interpretation of the resulting closure phases on the Poincaré sphere is presented. Since unpolarized sources are used, the actual solutions for leakage parameters is subject to a degeneracy which is discussed. This however, does not affect the correction of closure errors in our scheme.