Pixel space convolution for cosmic microwave background experiments

Fluxà, Pedro; Brewer, Michael K.; Dünner, Rolando

doi:10.1088/1475-7516/2020/02/030

Cited by 4 publications

(6 citation statements)

References 27 publications

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“…Two colocated detectors sharing a feed have sensitivity to orthogonal states of linear polarization. When these point at slightly different locations on the sky, the resulting differential pointing can lead to nonzero polarization systematics in a pair-differencing experiment (Shimon et al 2008;Miller et al 2009;Fluxá et al 2020). Figure 5 shows the differential pointing between colocated detectors for 115 feeds across the focal plane, which have both detectors operational.…”

Section: Differential Pointingmentioning

confidence: 99%

“…A beam mismatch due to differential shape and gain between the beams of detectors with orthogonal polarization axes sharing a common feed can introduce systematics in the polarization analysis (Shimon et al 2008;Fluxá et al 2020) if not properly accounted for. However, since our cosmological analysis pipeline works with individual detectors, the impact of these systematics is negligible.…”

Section: Beam Measurementsmentioning

confidence: 99%

“…The impact of the systematics is assessed by comparing the EE/BB autocorrelation spectra before and after the inclusion of systematics. For the ghosting beam and dipolar T → P leakage simulations, the corresponding beams are convolved with the polarization and temperature component of CMB simulations respectively, using a pixelized beam convolutor pisco (Fluxá et al 2020). The resulting power spectra are shown in Figure 16; in both cases, the systematics errors are subdominant compared to the cosmological signal.…”

Section: Impact Of Beam Systematicsmentioning

confidence: 99%

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Cosmology Large Angular Scale Surveyor (CLASS): 90 GHz Telescope Pointing, Beam Profile, Window Function, and Polarization Performance

Datta,

Brewer,

Couto

et al. 2024

ApJS

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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 CMB polarization to constrain the tensor-to-scalar ratio and the optical depth to last scattering. This paper presents the optical characterization of the 90 GHz telescope. Observations of the Moon establish the pointing while dedicated observations of Jupiter are used for beam calibration. The standard deviations of the pointing error in azimuth, elevation, and boresight angle are 1.′3, 2.′1, and 2.′0, respectively, over the first 3 yr of observations. This corresponds to a pointing uncertainty ∼7% of the beam’s full width at half-maximum (FWHM). The effective azimuthally symmetrized instrument 1D beam estimated at 90 GHz has an FWHM of 0.°620 ± 0.°003 and a solid angle of 138.7 ± 0.6(stats.) ± 1.1(sys.) μsr integrated to a radius of 4°. The corresponding beam window function drops to b ℓ 2 = 0.93 , 0.71 , 0.14 at ℓ = 30, 100, 300, respectively. Far-sidelobes are studied using detector-centered intensity maps of the Moon and measured to be at a level of 10−3 or below relative to the peak. The polarization angle of Tau A estimated from preliminary survey maps is 149°.6 ± 0°.2(stats.) in equatorial coordinates. The instrumental temperature-to-polarization (T → P) leakage fraction, inferred from per-detector demodulated Jupiter scan data, has a monopole component at the level of 1.7 × 10−3, a dipole component with an amplitude of 4.3 × 10−3, with no evidence of quadrupolar leakage.

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Section: Differential Pointingmentioning

confidence: 99%

Section: Beam Measurementsmentioning

confidence: 99%

Section: Impact Of Beam Systematicsmentioning

confidence: 99%

See 1 more Smart Citation

Cosmology Large Angular Scale Surveyor (CLASS): 90 GHz Telescope Pointing, Beam Profile, Window Function, and Polarization Performance

Datta,

Brewer,

Couto

et al. 2024

ApJS

View full text Add to dashboard Cite

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“…Furthermore, the T-to-P effect can be simulated by convolving the sky temperature signal with the dipolar beam estimated from the Moon maps for each detector and each VPM grid. The convolution was performed in the pixel space using pisco (Fluxá et al 2020). The bottom-right panel of Figure 16 shows a simulation of the bottom-left panel made by convolving the WMAP Q-band temperature maps scaled to the CLASS bandpass by the dipolar leakage beams and differencing the simulated +45°and −45°l eakage maps.…”

Section: Temperature-to-polarization Leakagementioning

confidence: 99%

CLASS Data Pipeline and Maps for 40 GHz Observations through 2022

Li 李,

Eimer,

Osumi

et al. 2023

ApJ

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The Cosmology Large Angular Scale Surveyor (CLASS) is a telescope array that observes the cosmic microwave background over 75% of the sky from the Atacama Desert, Chile, at frequency bands centered near 40, 90, 150, and 220 GHz. This paper describes the CLASS data pipeline and maps for 40 GHz observations conducted from 2016 August to 2022 May. We demonstrate how well the CLASS survey strategy, with rapid (∼10 Hz) front-end modulation, recovers the large-scale Galactic polarization signal from the ground: the mapping transfer function recovers ∼67% (85%) of EE and BB (VV) power at ℓ = 20 and ∼35% (47%) at ℓ = 10. We present linear and circular polarization maps over 75% of the sky. Simulations based on the data imply the maps have a white noise level of 110 μ K arcmin and correlated noise component rising at low-ℓ as ℓ −2.4. The transfer-function-corrected low-ℓ component is comparable to the white noise at the angular knee frequencies of ℓ ≈ 18 (linear polarization) and ℓ ≈ 12 (circular polarization). Finally, we present simulations of the level at which expected sources of systematic error bias the measurements, finding subpercent bias for the Λ cold dark matter EE power spectra. Bias from E-to-B leakage due to the data reduction pipeline and polarization angle uncertainty approaches the expected level for an r = 0.01 BB power spectrum. Improvements to the instrument calibration and the data pipeline will decrease this bias.

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“…There are of course no perfect replacements to these full realistic TOD simulations and in recent years this has led to great improvements in the efficiency of these simulations particularly in the time consuming implementation of beam convolution (see e.g. Mitra et al 2011;Wallis et al 2014;Duivenvoorden et al 2019;Fluxá et al 2020). However these remain computationally heavy processes and as such implementations which can mimic some of the salient features of a full TOD simulation in a less time costly approach are desirable.…”

Section: Introductionmentioning

confidence: 99%

Fast map-based simulations of systematics in CMB surveys including effects of the scanning strategy

McCallum¹,

Thomas²,

Brown³

2022

Monthly Notices of the Royal Astronomical Society

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We present approaches to quickly simulate systematics affecting CMB observations, including the effects of the scanning strategy. Using summary properties of the scan we capture features of full time ordered data (TOD) simulations, allowing maps and power spectra to be generated at much improved speed for a number of systematics – the cases we present experienced speed ups of 3-4 orders of magnitude when implementing the map-based approaches. We demonstrate the effectiveness of the approaches at capturing the salient features of the scan by directly comparing to full TOD simulations – seeing agreement at sub-percent levels of accuracy. We simulate the effects of differential gain, pointing, and ellipticity to show the effectiveness of the approaches, but note that one could extend these techniques to other systematics. We finally show how to apply these fast map-based simulations of systematic effects to a full focal plane showing their ability to incorporate thousands of detectors as seen in modern CMB experiments.

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Pixel space convolution for cosmic microwave background experiments

Cited by 4 publications

References 27 publications

Cosmology Large Angular Scale Surveyor (CLASS): 90 GHz Telescope Pointing, Beam Profile, Window Function, and Polarization Performance

Cosmology Large Angular Scale Surveyor (CLASS): 90 GHz Telescope Pointing, Beam Profile, Window Function, and Polarization Performance

CLASS Data Pipeline and Maps for 40 GHz Observations through 2022

Fast map-based simulations of systematics in CMB surveys including effects of the scanning strategy

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