Two-year Cosmology Large Angular Scale Surveyor (CLASS) Observations: 40 GHz Telescope Pointing, Beam Profile, Window Function, and Polarization Performance

Abstract

The Cosmology Large Angular Scale Surveyor (CLASS) is a telescope array that observes the cosmic microwave background (CMB) over 75% of the sky from the Atacama Desert, Chile, at frequency bands centered near 40, 90, 150, and 220 GHz. CLASS measures the large angular scale (1 • θ 90 • ) CMB polarization to constrain the tensor-to-scalar ratio at the r ∼ 0.01 level and the optical depth to last scattering to the sample variance limit. This paper presents the optical characterization of the 40 GHz telescope during its first observation era, from September 2016 to February 2018. High signal-to-noise observations of the Moon establish the pointing and beam calibration. The telescope boresight pointing variation is < 0.023 • (< 1.6% of the beam's full width at half maximum (FWHM)). We estimate beam parameters per detector and in aggregate, as in the CMB survey maps. The aggregate beam has a FWHM of 1.579 • ± .001 • and a solid angle of 838 ± 6 µsr, consistent with physical optics simulations. The corresponding beam window function has sub-percent error per multipole at < 200. An extended 90 • beam map reveals no significant far sidelobes. The observed Moon polarization shows that the instrument polarization angles are consistent with the optical model and that the temperature-topolarization leakage fraction is < 10 −4 (95% C.L.). We find that the Moon-based results are consistent with measurements of M42, RCW 38, and Tau A from CLASS's CMB survey data. In particular, Tau A measurements establish degree-level precision for instrument polarization angles.

New Extraction of the Cosmic Birefringence from the Planck 2018 Polarization Data

“…improve our measurement, one can apply our method to both the ongoing [23,[40][41][42][43] and future [44][45][46][47][48] CMB polarization experiments.…”

Constraining $M_ν$ with the Bispectrum II: The Total Information Content of the Galaxy Bispectrum

“…Therefore, when we analyze BOSS with a simulation-based approach later in the series, we will use an extended HOD framework that includes both assembly bias and velocity biases (e.g. Hearin et al 2016;Vakili & Hahn 2019;Wibking et al 2019;Zhai et al 2019;Salcedo et al 2020;Xu et al 2020). Given the improvements we see in HOD parameter constraints from B g 0 in Figure 3, B g 0 also has the potential to better constrain the assembly bias parameters and improve our understanding of the galaxy-halo connection.…”

“…CMB-S4) and will not directly constrain τ (Abazajian et al 2016). Although, the CLASS experiment aims to improve τ constraints from the ground (Xu et al 2020), future space-based experiments such as LiteBIRD 1 and LiteCOrE 2 , which have the greatest potential to precisely measure τ , have yet to be confirmed.…”

The Crab Nebula as a Calibrator for Wide-beam Cosmic Microwave Background Polarization Surveys

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