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Register a new userDegree-Scale CMB Polarization Measurements from Three Years of BICEP1 Data
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BICEP1 is a millimeter-wavelength telescope designed specifically to measure the inflationary B-mode polarization of the Cosmic Microwave Background (CMB) at degree angular scales. We present results from an analysis of the data acquired during three seasons of observations at the South Pole (2006 to 2008). This work extends the two-year result published in Chiang et al. (2010), with additional data from the third season and relaxed detector-selection criteria. This analysis also introduces a more comprehensive estimation of band-power window functions, improved likelihood estimation methods and a new technique for deprojecting monopole temperature-to-polarization leakage which reduces this class of systematic uncertainty to a negligible level. We present maps of temperature, E- and B-mode polarization, and their associated angular power spectra. The improvement in the map noise level and polarization spectra error bars are consistent with the 52% increase in integration time relative to Chiang et al. (2010). We confirm both self-consistency of the polarization data and consistency with the two-year results. We measure the angular power spectra at 21 <= l <= 335 and find that the EE spectrum is consistent with Lambda Cold Dark Matter (LCDM) cosmology, with the first acoustic peak of the EE spectrum now detected at 15sigma. The BB spectrum remains consistent with zero. From B-modes only, we constrain the tensor-to-scalar ratio to r = 0.03+0.27-0.23, or r < 0.70 at 95% confidence level.
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Cosmic Microwave Background (CMB) polarimeters aspire to measure the faint $B$-mode signature predicted to arise from inflationary gravitational waves. They also have the potential to constrain cosmic birefringence which would produce non-zero expectation values for the CMBs $TB$ and $EB$ spectra. However, instrumental systematic effects can also cause these $TB$ and $EB$ correlations to be non-zero. In particular, an overall miscalibration of the polarization orientation of the detectors produces $TB$ and $EB$ spectra which are degenerate with isotropic cosmological birefringence, while also introducing a small but predictable bias on the $BB$ spectrum. The bicep three-year spectra, which use our standard calibration of detector polarization angles from a dielectric sheet, are consistent with a polarization rotation of $alpha = -2.77^circ pm 0.86^circ text{(statistical)} pm 1.3^circ text{(systematic)}$. We revise the estimate of systematic error on the polarization rotation angle from the two-year analysis by comparing multiple calibration methods. We investigate the polarization rotation for the bicep 100 GHz and 150 GHz bands separately to investigate theoretical models that produce frequency-dependent cosmic birefringence. We find no evidence in the data supporting either these models or Faraday rotation of the CMB polarization by the Milky Way galaxys magnetic field. If we assume that there is no cosmic birefringence, we can use the $TB$ and $EB$ spectra to calibrate detector polarization orientations, thus reducing bias of the cosmological $B$-mode spectrum from leaked $E$-modes due to possible polarization orientation miscalibration. After applying this self-calibration process, we find that the upper limit on the tensor-to-scalar ratio decreases slightly, from $r<0.70$ to $r<0.65$ at $95%$ confidence.
The BICEP/Keck Array experiment is a series of small-aperture refracting telescopes observing degree-scale Cosmic Microwave Background polarization from the South Pole in search of a primordial $B$-mode signature. As a pair differencing experiment, an important systematic that must be controlled is the differential beam response between the co-located, orthogonally polarized detectors. We use high-fidelity, in-situ measurements of the beam response to estimate the temperature-to-polarization (T $rightarrow$ P) leakage in our latest data including observations from 2016 through 2018. This includes three years of BICEP3 observing at 95 GHz, and multifrequency data from Keck Array. Here we present band-averaged far-field beam maps, differential beam mismatch, and residual beam power (after filtering out the leading difference modes via deprojection) for these receivers. We show preliminary results of beam map simulations, which use these beam maps to observe a simulated temperature (no $Q/U$) sky to estimate T $rightarrow$ P leakage in our real data.
We study the propagation of a specific class of instrumental systematics to the reconstruction of the B-mode power spectrum of the cosmic microwave background (CMB). We focus on non-idealities of the half-wave plate (HWP), a polarization modulator that will be deployed by future CMB experiments, such as the phase-A satellite mission LiteBIRD. More in details, we study the effects of non-ideal HWP properties, such as transmittance, phase shift and cross-polarization. To this purpose, we develop a simple, yet stand-alone end-to-end simulation pipeline adapted to LiteBIRD. Through the latter, we analyze the effects of a possible mismatch between the measured frequency profiles of HWP properties (used in the mapmaking stage of the pipeline) and the actual profiles (used in the sky-scanning step). We simulate single-frequency, CMB-only observations to emphasize the effects of non-idealities on the BB power spectrum. We also consider multi-frequency observations to account for the frequency dependence of HWP properties and the contribution of foreground emission. We quantify the systematics effects in terms of a bias $Delta r$ on the tensor-to-scalar ratio $r$ with respect to the ideal case of no-systematics. We derive the accuracy requirements on the measurements of HWP properties by requiring $Delta r < 10^{-5}$ (1% of the expected LiteBIRD sensitivity on $r$). The analysis is introduced by a detailed presentation of the mathematical formalism employed in this work, including the use of the Jones and Mueller matrix representations.
BICEP3 is a 550 mm-aperture refracting telescope for polarimetry of radiation in the cosmic microwave background at 95 GHz. It adopts the methodology of BICEP1, BICEP2 and the Keck Array experiments - it possesses sufficient resolution to search for signatures of the inflation-induced cosmic gravitational-wave background while utilizing a compact design for ease of construction and to facilitate the characterization and mitigation of systematics. However, BICEP3 represents a significant breakthrough in per-receiver sensitivity, with a focal plane area 5$times$ larger than a BICEP2/Keck Array receiver and faster optics ($f/1.6$ vs. $f/2.4$). Large-aperture infrared-reflective metal-mesh filters and infrared-absorptive cold alumina filters and lenses were developed and implemented for its optics. The camera consists of 1280 dual-polarization pixels; each is a pair of orthogonal antenna arrays coupled to transition-edge sensor bolometers and read out by multiplexed SQUIDs. Upon deployment at the South Pole during the 2014-15 season, BICEP3 will have survey speed comparable to Keck Array 150 GHz (2013), and will significantly enhance spectral separation of primordial B-mode power from that of possible galactic dust contamination in the BICEP2 observation patch.
We present a new upper limit on CMB circular polarization from the 2015 flight of SPIDER, a balloon-borne telescope designed to search for $B$-mode linear polarization from cosmic inflation. Although the level of circular polarization in the CMB is predicted to be very small, experimental limits provide a valuable test of the underlying models. By exploiting the non-zero circular-to-linear polarization coupling of the HWP polarization modulators, data from SPIDERs 2015 Antarctic flight provide a constraint on Stokes $V$ at 95 and 150 GHz from $33<ell<307$. No other limits exist over this full range of angular scales, and SPIDER improves upon the previous limit by several orders of magnitude, providing 95% C.L. constraints on $ell (ell+1)C_{ell}^{VV}/(2pi)$ ranging from 141 $mu K ^2$ to 255 $mu K ^2$ at 150 GHz for a thermal CMB spectrum. As linear CMB polarization experiments become increasingly sensitive, the techniques described in this paper can be applied to obtain even stronger constraints on circular polarization.
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