The Simons Observatory: Detector Polarization Angle Calibration Using a Sparse Wire Grid with Initial Datasets of the Small-aperture Telescopes
Year: 2026
Type: article
Abstract: Improved measurements of B -modes in the cosmic microwave background can be obtained through accurate calibration of the orientation of detector antennas as projected onto the sky. Miscalibration of the detector polarization angle leads to a leakage of E -modes into B -modes, which can bias the detection of the latter. To achieve a σ ( r ) of 0.003, the Simons Observatory small-aperture telescopes are required to calibrate the global polarization angle on the sky with an accuracy ≲0 . ° 1. We demonstrate a fully remote-controllable calibration system using a “sparse wire grid,” which injects a rotatable linear polarized signal across the telescope’s focal plane. This calibration system is installed and operational on one of the small-aperture telescopes at its observing site at the Parque Astronómico in the Atacama desert in Chile. We developed a pipeline for the detector polarization angle calibration, and demonstrate it using initial data for 93 and 145 GHz frequency bands. The observed distribution of detector polarization angles is in agreement with the instrument design. Statistical uncertainties for the relatively calibrated polarization angles are 0 . ° 02 and 0 . ° 03 at 93 and 145 GHz, respectively. Systematic uncertainty was evaluated to be 0 . ° 08 at the hardware development and fabrication stage. Their sum in quadrature is less than 0 . ° 1.
Authors: Hironobu Nakata, Shunsuke Adachi, Kyohei Yamada, Michael Randall, Yutaro Kasai, Kam Arnold, Bryce Bixler, Yuji Chinone, Kevin T. Crowley, Nadia Dachlythra, Samuel Day-Weiss, Nicholas Galitzki, Serena Giardiello, Bradley R. Johnson, Brian Keating, Brian J. Koopman, Akito Kusaka, Jack Lashner, Federico Nati, Lyman Page, Daichi Sasaki, Yoshinori Sueno, Junya Suzuki, Osamu Tajima, Tran Tsan
Institutions: Kyoto University, Okayama University, Princeton University, University of California San Diego, High Energy Accelerator Research Organization, Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo, University of Milano-Bicocca, The University of Texas at Austin, Cardiff University, University of Virginia, Yale University, Lawrence Berkeley National Laboratory
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $4,499
Awards: Elucidating the Universe's Creation with Neutrinos based on International Science Collaborations, 宇宙背景放射の偏光観測を通した超高エネルギー物理の研究, Exploration of the origin of Big Bang - CMB observastion using the largest telescope array and cutting-edge superconducting technologies, SO:UK - A major UK contribution to Simons Observatory, Probing the origin of the Big-Bang and neutrino mass using the largest CMB telescope array to date, SO:UK - A major UK contribution to the Simons Observatory, Probing the origin of the universe using the largest CMB telescope arrays to date, G4085995257, G4253729788, G4582035553, The exploration of the primordial universe and the mystery of the dark cosmos through high-precision CMB polarimetry, Mid-scale RI-2: Advanced Millimeter Survey Instrumentation in Chile, G8562884025
OpenAlex ID: W7147264100