BICEP2. III. Instrumental Systematics
In a companion paper, we have reported a >5σ 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 reduces power in Bicep2's actual and null-test BB spectra 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 of ~10× below Bicep2's three-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) × 10^(−3).
© 2015 American Astronomical Society. Received 2015 February 9; accepted 2015 October 21; published 2015 November 23. Bicep2 was supported by the U.S. National Science Foundation under grants ANT-0742818 and ANT-1044978 (Caltech/Harvard) and ANT-0742592 and ANT-1110087 (Chicago/Minnesota). The development of antenna-coupled detector technology was supported by the JPL Research and Technology Development Fund and grants 06-ARPA206-0040 and 10-SAT10-0017 from the NASA APRA and SAT programs. The development and testing of focal planes were supported by the Gordon and Betty Moore Foundation at Caltech. Readout electronics were supported by a Canada Foundation for Innovation grant to UBC. The receiver development was supported in part by a grant from the W. M. Keck Foundation. Partial support for C. Sheehy was also provided by the Kavli Institute for Cosmological Physics at the University of Chicago through grant NSF PHY-1125897 and an endowment from the Kavli Foundation and its founder Fred Kavli. The computations in this paper were run on the Odyssey cluster supported by the FAS Science Division Research Computing Group at Harvard University. Tireless administrative support was provided by Irene Coyle and Kathy Deniston. We thank the staff of the U.S. Antarctic Program and in particular the South Pole Station without whose help this research would not have been possible. We thank all those who have contributed past efforts to the Bicep/Keck Array series of experiments, including the Bicep1 and Keck Array teams, as well as our colleagues on the Spider team with whom we coordinated receiver and detector development efforts at Caltech. We dedicate this paper to the memory of Andrew Lange, whom we sorely miss.
Published - Ade_2015p110.pdf
Submitted - 1502.00608v2.pdf