Optimal scan strategies for future CMB satellite experiments

TL;DR

This paper analyzes how different satellite scan strategies can reduce systematic errors in measuring the faint B-mode polarization of the CMB, proposing an optimal approach for future satellite experiments.

Contribution

It provides analytic models for systematic errors and identifies scan strategy features that effectively mitigate these errors in CMB polarization measurements.

Findings

Identified scan strategies that minimize systematic errors.

Developed analytic formulas for error estimation due to instrument imperfections.

Proposed a practical scan strategy for ESA's future CMB satellite mission.

Abstract

The B-mode polarisation power spectrum in the Cosmic Microwave Background (CMB) is about four orders of magnitude fainter than the CMB temperature power spectrum. Any instrumental imperfections that couple temperature fluctuations to B-mode polarisation must therefore be carefully controlled and/or removed. We investigate the role that a scan strategy can have in mitigating certain common systematics by averaging systematic errors down with many crossing angles. We present approximate analytic forms for the error on the recovered B-mode power spectrum that would result from differential gain, differential pointing and differential ellipticity for the case where two detector pairs are used in a polarisation experiment. We use these analytic predictions to search the parameter space of common satellite scan strategies in order to identify those features of a scan strategy that have most impact in mitigating systematic effects. As an example we go on to identify a scan strategy suitable for the CMB satellite proposed for the ESA M5 call. considering the practical considerations of fuel requirement, data rate and the relative orientation of the telescope to the earth. Having chosen a scan strategy we then go on to investigate the suitability of the scan strategy.