A new map-making algorithm for CMB polarisation experiments

TL;DR

This paper introduces two innovative map-making algorithms for CMB polarisation experiments that effectively eliminate temperature-to-polarisation leakage systematics without prior knowledge of instrument imperfections, enhancing the accuracy of polarisation maps.

Contribution

The paper presents two new algorithms that remove temperature leakage systematics directly from time-ordered data, adaptable to different scan strategies and capable of identifying specific systematic errors.

Findings

Algorithms successfully remove temperature-to-polarisation leakage in simulations.

Effective in identifying systematic errors with specific spin properties.

Applicable to realistic scan strategies and instrumental noise conditions.

Abstract

With the temperature power spectrum of the cosmic microwave background (CMB) at least four orders of magnitude larger than the B-mode polarisation power spectrum, any instrumental imperfections that couple temperature to polarisation must be carefully controlled and/or removed. Here we present two new map-making algorithms that can create polarisation maps that are clean of temperature-to-polarisation leakage systematics due to differential gain and pointing between a detector pair. Where a half wave plate is used, we show that the spin-2 systematic due to differential ellipticity can also by removed using our algorithms. The algorithms require no prior knowledge of the imperfections or temperature sky to remove the temperature leakage. Instead, they calculate the systematic and polarisation maps in one step directly from the time ordered data (TOD). The first algorithm is designed to work with scan strategies that have a good range of crossing angles for each map pixel and the second for scan strategies that have a limited range of crossing angles. The first algorithm can also be used to identify if systematic errors that have a particular spin are present in a TOD. We demonstrate the use of both algorithms and the ability to identify systematics with simulations of TOD with realistic scan strategies and instrumental noise.