BICEP2 III: Instrumental Systematics

Abstract

In a companion paper we have reported a $>5\sigma$ detection of degree scale $B$-mode polarization at 150 GHz by the BICEP2 experiment. Here we provide a detailed study of potential instrumental systematic contamination to that measurement. We focus extensively on spurious polarization that can potentially arise from beam imperfections. We present a heuristic classification of beam imperfections according to their symmetries and uniformities, and discuss how resulting contamination adds or cancels in maps that combine observations made at multiple orientations of the telescope about its boresight axis. We introduce a technique, which we call "deprojection", for filtering the leading order beam-induced contamination from time ordered data, and show that it removes power from BICEP2's $BB$ spectrum consistent with predictions using high signal-to-noise beam shape measurements. We detail the simulation pipeline that we use to directly simulate instrumental systematics and the calibration data used as input to that pipeline. Finally, we present the constraints on $BB$ contamination from individual sources of potential systematics. We find that systematics contribute $BB$ power that is a factor $\sim 10\times$ below BICEP2's 3-year statistical uncertainty, and negligible compared to the observed $BB$ signal. The contribution to the best-fit tensor/scalar ratio is at a level equivalent to $r=(3-6)\times 10^{-3}$.

26 pages, 16 figures, higher quality figures available at http://bicepkeck.org

References in corpus (10)

• CMB Polarization Systematics Due to Beam Asymmetry: Impact on Inflationary Science
• Self-Calibration of CMB Polarization Experiments
• BICEP2 / Keck Array V: Measurements of B-mode Polarization at Degree Angular Scales and 150 GHz by the Keck Array
• Second Season QUIET Observations: Measurements of the CMB Polarization Power Spectrum at 95 GHz
• CMB Polarization can constrain cosmology better than CMB temperature
• Systematic errors in cosmic microwave background polarization measurements
• Antenna-coupled TES bolometers used in BICEP2, Keck array, and SPIDER
• The Robinson Gravitational Wave Background Telescope (BICEP): a bolometric large angular scale CMB polarimeter
• BICEP2/Keck Array IV: Optical Characterization and Performance of the BICEP2 and Keck Array Experiments
• Antenna-coupled TES bolometer arrays for CMB polarimetry

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