Removing beam asymmetry bias in precision CMB temperature and polarisation experiments

Abstract

Asymmetric beams can create significant bias in estimates of the power spectra from CMB experiments. With the temperature power spectrum many orders of magnitude stronger than the B-mode power spectrum any systematic error that couples the two must be carefully controlled and/or removed. Here, we derive unbiased estimators for the CMB temperature and polarisation power spectra taking into account general beams and general scan strategies. A simple consequence of asymmetric beams is that, even with an ideal scan strategy where every sky pixel is seen at every orientation, there will be residual coupling from temperature power to B-mode power if the orientation of the beam asymmetry is not aligned with the orientation of the co-polarisation. We test our correction algorithm on simulations of two temperature-only experiments and demonstrate that it is unbiased. The simulated experiments use realistic scan strategies, noise levels and highly asymmetric beams. We also develop a map-making algorithm that is capable of removing beam asymmetry bias at the map level. We demonstrate its implementation using simulations and show that it is capable of accurately correcting both temperature and polarisation maps for all of the effects of beam asymmetry including the effects of temperature to polarisation leakage.

18 pages, 9 figures

References in corpus (8)

• Polarization Observations with the Cosmic Background Imager
• Measurement of the Cosmic Microwave Background Polarization Lensing Power Spectrum with the POLARBEAR experiment
• CMB Polarization Systematics Due to Beam Asymmetry: Impact on Inflationary Science
• Asymmetric Beams and CMB Statistical Anisotropy
• Systematic errors in cosmic microwave background polarization measurements
• Study of the Experimental Probe of Inflationary Cosmology (EPIC)-Intemediate Mission for NASA's Einstein Inflation Probe
• The Large-Scale Polarization Explorer (LSPE)
• CMB polarization TE power spectrum estimation with non-circular beam

Cited by in corpus (9)

• CMB-S4: Forecasting Constraints on Primordial Gravitational Waves
• QuickPol: Fast calculation of effective beam matrices for CMB polarization
• Optimal scan strategies for future CMB satellite experiments
• Instrumental systematics biases in CMB lensing reconstruction: a simulation-based assessment
• Full-sky beam convolution for cosmic microwave background applications
• Spin characterisation of systematics in CMB surveys -- a comprehensive formalism
• A new map-making algorithm for CMB polarisation experiments
• Consequences of constant elevation scans for instrumental systematics in Cosmic Microwave Background Experiments
• Fast map-based simulations of systematics in CMB surveys including effects of the scanning strategy