Dual differential polarimetry. A technique to recover polarimetric information from dual polarization observations

TL;DR

This paper introduces a novel dual differential polarimetry technique that enables extraction of full-polarization information from dual-polarization interferometric observations, expanding the capabilities of current mm/submm arrays like ALMA.

Contribution

The paper presents a new method that derives full-polarization data from dual-polarization observations, reducing the need for full-polarization mode and extensive calibration.

Findings

Enables recovery of full-polarization information from dual-polarization data.

Applicable to sources with complex structures.

Inspired by Earth-rotation polarization synthesis.

Abstract

Current mm/submm interferometers, like the Atacama Large mm/submm Array (ALMA), use receivers that register the sky signal in a linear polarization basis. In the case of observations performed in full-polarization mode (where the cross-correlations are computed among all the polarization channels) it is possible to reconstruct the full-polarization brightness distribution of the observed sources, as long as a proper calibration of delay offsets and leakage among polarization channels can be performed. Observations of calibrators, preferably with some linear polarization, with a good parallactic angle coverage are usually needed for such a calibration. In principle, dual-polarization observations only allow us to recover the Stokes $I$ intensity distribution of the sources, regardless of the parallactic angle coverage of the observations. In this paper, we present a novel technique of dual differential polarimetry that makes it possible to obtain information related to the full-polarization brightness distribution of the observed sources from dual-polarization observations. This technique is inspired in the Earth-rotation polarization synthesis and can be applied even to sources with complex structures.