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.
Bicep is a ground-based millimeter-wave bolometric array designed to target the primordial gravity wave signature
on the B-mode 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.
The Robinson Telescope (BICEP) is a ground-based millimeter-wave bolometric array designed to study the polarization of the cosmic microwave background radiation (CMB) and galactic foreground emission. Such measurements probe the energy scale of the inflationary epoch, tighten constraints on cosmological parameters, and verify our current understanding of CMB physics. Robinson consists of a 250-mm aperture refractive telescope that provides an instantaneous field-of-view of 17° with angular resolution of 55' and 37' at 100 GHz and 150 GHz, respectively. Forty-nine pair of polarization-sensitive bolometers are cooled to 250 mK using a <sup>4</sup>He/<sup>3</sup>He/<sup>3</sup>He sorption fridge system, and coupled to incoming radiation via corrugated feed horns. The all-refractive optics is cooled to 4 K to minimize polarization systematics and instrument loading. The fully steerable 3-axis mount is capable of continuous boresight rotation or azimuth scanning at speeds up to 5 deg/s. Robinson has begun its first season of observation at the South Pole. Given the measured performance of the instrument along with the excellent observing environment, Robinson will measure the E-mode polarization with high sensitivity, and probe for the B-modes to unprecedented depths. In this paper we discuss aspects of the instrument design and their scientific motivations, scanning and operational strategies, and the results of initial testing and observations.