The Simons Observatory: modeling optical systematics in the Large Aperture Telescope

Weak gravitational lensing of the cosmic microwave background (CMB) is an important cosmological tool that allows us to learn about the structure, composition and evolution of the Universe. Upcoming CMB experiments, such as the Simons Observatory (SO), will provide high-resolution and low-noise CMB measurements. We consider the impact of instrumental systematics on the corresponding high-precision lensing reconstruction power spectrum measurements. We simulate CMB temperature and polarization maps for an SO-like instrument and potential scanning strategy, and explore systematics relating to beam asymmetries and offsets, boresight pointing, polarization angle, gain drifts, gain calibration and electric crosstalk. Our analysis shows that the majority of the biases induced by the systematics we modeled are below a detection level of ∼ 0.6σ. We discuss potential mitigation techniques to further reduce the impact of the more significant systematics, and pave the way for future lensing-related systematics analyses.

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“…A good demonstration of these correlations is shown in Ref [28],. where a more comprehensive review of the SO optics can also be found.…”

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confidence: 69%

Instrumental systematics biases in CMB lensing reconstruction: A simulation-based assessment

et al. 2021

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“…The Simons Observatory (SO; Galitzki et al 2018; The Simons Observatory Collaboration 2019) is a next-generation CMB experiment consisting of three 0.42 m small-aperture telescopes (SATs; Ali et al 2020) and one 6 m Large Aperture Telescope (LAT; Parshley et al 2018) in the Atacama Desert of Chile. The LAT utilizes a crossed-Dragone optical design with a pair of 6 m mirrors (Gallardo et al 2018;Gudmundsson et al 2021). The Large Aperture Telescope Receiver (LATR; Orlowski-Scherer et al 2018;Zhu et al 2018; can contain up to 13 optics tubes (OTs) and will cover six frequency bands centered around 27, 39, 93, 145, 225, and 280 GHz with polarization-sensitive dichroic pixels.…”

Section: Introductionmentioning

confidence: 99%

The Simons Observatory Large Aperture Telescope Receiver

Zhu

Bhandarkar

Coppi

et al. 2021

ApJS

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The Simons Observatory is a ground-based cosmic microwave background experiment that consists of three 0.4 m small-aperture telescopes and one 6 m Large Aperture Telescope, located at an elevation of 5300 m on Cerro Toco in Chile. The Simons Observatory Large Aperture Telescope Receiver (LATR) is the cryogenic camera that will be coupled to the Large Aperture Telescope. The resulting instrument will produce arcminute-resolution millimeter-wave maps of half the sky with unprecedented precision. The LATR is the largest cryogenic millimeter-wave camera built to date, with a diameter of 2.4 m and a length of 2.6 m. The coldest stage of the camera is cooled to 100 mK, the operating temperature of the bolometric detectors with bands centered around 27, 39, 93, 145, 225, and 280 GHz. Ultimately, the LATR will accommodate 13 40 cm diameter optics tubes, each with three detector wafers and a total of 62,000 detectors. The LATR design must simultaneously maintain the optical alignment of the system, control stray light, provide cryogenic isolation, limit thermal gradients, and minimize the time to cool the system from room temperature to 100 mK. The interplay between these competing factors poses unique challenges. We discuss the trade studies involved with the design, the final optimization, the construction, and ultimate performance of the system.

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“…The SO LAT is shown in Figure 1 and described in [8]. We compute its beam pattern in the near-field and far-field using physical optics [4,30] implemented in a code we call HoloSim-ML, available at GitHub.com/McMahonCosmologyLab [31].…”

Section: Beam Simulationmentioning

confidence: 99%

“…Simons Observatory (SO) is an ensemble of millimeter-wave telescopes which will observe the cosmic microwave background (CMB) temperature and polarization signals [1,2]. SO comprises one Large Aperture Telescope (LAT) [3][4][5] and three Small Aperture Telescopes (SAT) [6] which together will measure the temperature and polarization anisotropy of the CMB from several degrees to arc-minute angular scales.…”

Section: Introductionmentioning

confidence: 99%

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Simons Observatory HoloSim-ML: machine learning applied to the efficient analysis of radio holography measurements of complex optical systems

et al. 2021

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Near-field radio holography is a common method for measuring and aligning mirror surfaces for millimeter and sub-millimeter telescopes. In instruments with more than a single mirror, degeneracies arise in the holography measurement, requiring multiple measurements and new fitting methods. We present HoloSim-ML, a Python code for beam simulation and analysis of radio holography data from complex optical systems. This code uses machine learning to efficiently determine the position of hundreds of mirror adjusters on multiple mirrors with few micrometer accuracy. We apply this approach to the example of the Simons Observatory 6 m telescope.

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The Simons Observatory: modeling optical systematics in the Large Aperture Telescope

Cited by 26 publications

References 34 publications

Instrumental systematics biases in CMB lensing reconstruction: A simulation-based assessment

Instrumental systematics biases in CMB lensing reconstruction: A simulation-based assessment

The Simons Observatory Large Aperture Telescope Receiver

Simons Observatory HoloSim-ML: machine learning applied to the efficient analysis of radio holography measurements of complex optical systems

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