CMB polarimetry with BICEP: instrument characterization, calibration, and performance

BICEP is a ground-based millimeter-wave bolometric array designed to target the primordial gravity wave signature on the polarization of the cosmic microwave background (CMB) at degree angular scales. Currently in its third year of operation at the South Pole, BICEP is measuring the CMB polarization with unprecedented sensitivity at 100 and 150 GHz in the cleanest available 2% of the sky, as well as deriving independent constraints on the diffuse polarized foregrounds with select observations on and off the Galactic plane. Instrument calibrations are discussed in the context of rigorous control of systematic errors, and the performance during the first two years of the experiment is reviewed.Comment: 12 pages, 15 figures, updated version of a paper accepted for Millimeter and Submillimeter Detectors and Instrumentation for Astronomy IV, Proceedings of SPIE, 7020, 200

Absolute polarization angle calibration using polarized diffuse Galactic emission observed by BICEP

We present a method of cross-calibrating the polarization angle of a polarimeter using BICEP Galactic observations. \bicep\ was a ground based experiment using an array of 49 pairs of polarization sensitive bolometers observing from the geographic South Pole at 100 and 150 GHz. The BICEP polarimeter is calibrated to +/-0.01 in cross-polarization and less than +/-0.7 degrees in absolute polarization orientation. BICEP observed the temperature and polarization of the Galactic plane (R.A= 100 degrees ~ 270 degrees and Dec. = -67 degrees ~ -48 degrees). We show that the statistical error in the 100 GHz BICEP Galaxy map can constrain the polarization angle offset of WMAP Wband to 0.6 degrees +\- 1.4 degrees. The expected 1 sigma errors on the polarization angle cross-calibration for Planck or EPIC are 1.3 degrees and 0.3 degrees at 100 and 150 GHz, respectively. We also discuss the expected improvement of the BICEP Galactic field observations with forthcoming BICEP2 and Keck observations.Comment: 13 pages, 10 figures and 2 tables. To appear in Proceedings of SPIE Astronomical Telescopes and Instrumentation 201

Characterization of the BICEP Telescope for High-precision Cosmic Microwave Background Polarimetry

The Background Imaging of Cosmic Extragalactic Polarization (BICEP) experiment was designed specifically to search for the signature of inflationary gravitational waves in the polarization of the cosmic microwave background (CMB). Using a novel small-aperture refractor and 49 pairs of polarization-sensitive bolometers, BICEP has completed three years of successful observations at the South Pole beginning in 2006 February. To constrain the amplitude of the inflationary B-mode polarization, which is expected to be at least 7 orders of magnitude fainter than the 3 K CMB intensity, precise control of systematic effects is essential. This paper describes the characterization of potential systematic errors for the BICEP experiment, supplementing a companion paper on the initial cosmological results. Using the analysis pipelines for the experiment, we have simulated the impact of systematic errors on the B-mode polarization measurement. Guided by these simulations, we have established benchmarks for the characterization of critical instrumental properties including bolometer relative gains, beam mismatch, polarization orientation, telescope pointing, sidelobes, thermal stability, and timestream noise model. A comparison of the benchmarks with the measured values shows that we have characterized the instrument adequately to ensure that systematic errors do not limit BICEP's two-year results, and identifies which future refinements are likely necessary to probe inflationary B-mode polarization down to levels below a tensor-to-scalar ratio r = 0.1.Astronom

Millimeter-wave polarimetry instrumentation and analysis

The chapters in this thesis roughly follow a reverse chronological order of my work in graduate school. Chapter 1 is the culmination of work with Dr. Dowell at Caltech, motivated by Professor Keating, to study polarized Galactic emission. Although the main goal of BICEP was to search for CMB B-modes, observation time was also spent on the Galactic plane region. Initially the data were collected to understand Galactic emission as a foreground of CMB polarization; however, the final paper focused on studying Galactic physics and not the CMB. Through comparison of BICEP data to other experiments, different models of the polarization production were explored. This paper also served as the initial instrument paper for the 220 GHz hardware added to BICEP for the second and third observing seasons. Chapter 2 is the software analysis work related to the paper in Chapter 1 that either did not make it into the paper or did not pan out. To explore BICEP's capabilities and produce better maps different scan strategies were explored such as full 360° scans and elevation scanning. BICEP observations are contaminated on large scales by a noise source that has not been fully identified. Different mapmaking methods were explored to remove this systematic as well as 1/ f noise and telescope systematics to maximize recovered signal. Chapter 3 represents a sample of contributions to the BICEP telescope and the UCSD FTS. To characterize the spectral response of the BICEP telescope and the faraday rotation modulators, I helped design and construct the UCSD including layout and optical design, synthesizing wire grids, integrating the system with our lab's test cryostat, and developing software and analysis tools. My main contribution to the CMB polarization work on BICEP was analysis of calibration data. Specifically I talk about my work to understand the beams and differential pointing from observations of the Moon. Chapter 4 represents my work on Faraday Rotation devices. Initially, these devices were developed to overcome 1/ f noise and some beam systematics; however, the usage of these devices were limited and their full capabilities were not tested. The devices were shown to work generally as designed and were followed up by similar devices developed and deployed for the MBI-4 experimen

Absolute polarization angle calibration using polarized diffuse Galactic emission observed by BICEP

We present a method of cross-calibrating the polarization angle of a polarimeter using Bicep Galactic observations. Bicep was a ground based experiment using an array of 49 pairs of polarization sensitive bolometers observing from the geographic South Pole at 100 and 150 GHz. The Bicep polarimeter is calibrated to ±0.01 in cross-polarization and less than ±0.7◦ in absolute polarization orientation. Bicep observed the temperature and polarization of the Galactic plane (R.A = 100◦ ∼ 270◦ and Dec. = −67◦ ∼ −48◦). We show that the statistical error in the 100 GHz Bicep Galaxy map can constrain the polarization angle offset of Wmap W band to 0.6◦ ± 1.4◦. The expected 1σ errors on the polarization angle cross-calibration for Planck or EPIC are 1.3◦ and 0.3◦ at 100 and 150 GHz, respectively. We also discuss the expected improvement of the Bicep Galactic field observations with forthcoming Bicep2 and Keck observations.Astronom