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A Measurement of Atmospheric Circular Polarization with POLARBEAR

Fujino, Takuro [Yokohama National University (Japan)] (ORCID:0000000212117850)·Takakura, Satoru [High Energy Accelerator Research Organization (KEK), Tsukuba (Japan); University of Tokyo (Japan)] (ORCID:0000000194617519)·Arani, Shahed Shayan [University of California, San Diego, CA (United States)] (ORCID:0009000541682858)·Barron, Darcy [University of New Mexico, Albuquerque, NM (United States)] (ORCID:0000000216235651)·Baccigalupi, Carlo [International School for Advanced Studies (SISSA), Trieste (Italy); Istituto Nazionale di Fisica Nucleare (INFN), Trieste (Italy)] (ORCID:0000000282111630)·Chinone, Yuji [High Energy Accelerator Research Organization (KEK), Tsukuba (Japan); University of Tokyo (Japan). Kavli Institute for the Physics and Mathematics of the Universe (WPI)] (ORCID:000000023266857X)·Errard, Josquin [Université Paris Cité (France); Centre National de la Recherche Scientifique (CNRS), Paris (France). AstroParticule et Cosmologie (APC)] (ORCID:0000000214190031)·Fabbian, Giulio [University of Cambridge (United Kingdom)] (ORCID:0000000232554695)·Feng, Chang [University of Science and Technology of China, Hefei (China)] (ORCID:0000000174385896)·Halverson, Nils W. [University of Colorado, Boulder, CO (United States)] (ORCID:0000000326069340)·Hasegawa, Masaya [High Energy Accelerator Research Organization (KEK), Tsukuba (Japan)] (ORCID:0000000314431082)·Hazumi, Masashi [High Energy Accelerator Research Organization (KEK), Tsukuba (Japan); University of Tokyo (Japan). Kavli Institute for the Physics and Mathematics of the Universe (WPI); Japan Aerospace Exploration Agency (ISAS/JAXA), Sagamihara, Kanagawa (Japan). Institute of Space and Astronautical Science; Graduate University for Advanced Studies, SOKENDAI, Kanagawa (Japan)] (ORCID:0000000168308309)·Jeong, Oliver [University of California, Berkeley, CA (United States)] (ORCID:0000000158937697)·Kaneko, Daisuke [High Energy Accelerator Research Organization (KEK), Tsukuba (Japan)] (ORCID:000000033917086X)·Keating, Brian [University of California, San Diego, CA (United States)] (ORCID:0000000331185514)·Kusaka, Akito [University of Tokyo (Japan); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)] (ORCID:0009000496312451)·Lee, Adrian [University of California, Berkeley, CA (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)] (ORCID:0000000331063218)·Matsumura, Tomotake [University of Tokyo (Japan). Kavli Institute for the Physics and Mathematics of the Universe (WPI)] (ORCID:0000000190020686)·Piccirillo, Lucio [University of Manchester (United Kingdom)] (ORCID:0000000178680841)·Reichardt, Christian L. [University of Melbourne, Parkville, VIC (Australia)] (ORCID:0000000322269169)·Sakaguri, Kana [University of Tokyo (Japan)] (ORCID:0000000156678118)·Siritanasak, Praween [National Astronomical Research Institute of Thailand, Chiangmai (Thailand)] (ORCID:0000000168301537)·Yamada, Kyohei [University of Tokyo (Japan)] (ORCID:0000000302212130)
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Abstract

At millimeter wavelengths, the atmospheric emission is circularly polarized owing to the Zeeman splitting of molecular oxygen by the Earth's magnetic field. We report a measurement of the signal in the 150 GHz band using 3 yr of observational data with the POLARBEAR project. Nonidealities of a continuously rotating half-wave plate (HWP) partially convert circularly polarized light to linearly polarized light. While POLARBEAR detectors are sensitive to linear polarization, this effect makes them sensitive to circular polarization. Although this was not the intended use, we utilized this conversion to measure circular polarization. We reconstruct the azimuthal gradient of the circular polarization signal and measure its dependency from the scanning direction and the detector bandpass. We compare the signal with a simulation based on atmospheric emission theory, the detector bandpass, and the HWP leakage spectrum model. We find the ratio of the observed azimuthal slope to the simulated slope is 0.92 ± 0.01(stat) ± 0.07(sys). This ratio corresponds to a brightness temperature of 3.8 mK at the effective band center of 121.8 GHz and bandwidth of 3.5 GHz estimated from representative detector bandpass and the spectrum of Zeeman emission. This result validates our understanding of the instrument and reinforces the feasibility of measuring the circular polarization using the imperfection of continuously rotating HWP. Continuously rotating HWP is popular in ongoing and future cosmic microwave background experiments to modulate the polarized signal. This work shows a method for signal extraction and leakage subtraction that can help measure circular polarization in such experiments.

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Fujino, Takuro [Yokohama National University (Japan)] (ORCID:0000000212117850), Takakura, Satoru [High Energy Accelerator Research Organization (KEK), Tsukuba (Japan); University of Tokyo (Japan)] (ORCID:0000000194617519), Arani, Shahed Shayan [University of California, San Diego, CA (United States)] (ORCID:0009000541682858), Barron, Darcy [University of New Mexico, Albuquerque, NM (United States)] (ORCID:0000000216235651), Baccigalupi, Carlo [International School for Advanced Studies (SISSA), Trieste (Italy); Istituto Nazionale di Fisica Nucleare (INFN), Trieste (Italy)] (ORCID:0000000282111630), Chinone, Yuji [High Energy Accelerator Research Organization (KEK), Tsukuba (Japan); University of Tokyo (Japan). Kavli Institute for the Physics and Mathematics of the Universe (WPI)] (ORCID:000000023266857X), Errard, Josquin [Université Paris Cité (France); Centre National de la Recherche Scientifique (CNRS), Paris (France). AstroParticule et Cosmologie (APC)] (ORCID:0000000214190031), Fabbian, Giulio [University of Cambridge (United Kingdom)] (ORCID:0000000232554695), Feng, Chang [University of Science and Technology of China, Hefei (China)] (ORCID:0000000174385896), Halverson, Nils W. [University of Colorado, Boulder, CO (United States)] (ORCID:0000000326069340), Hasegawa, Masaya [High Energy Accelerator Research Organization (KEK), Tsukuba (Japan)] (ORCID:0000000314431082), Hazumi, Masashi [High Energy Accelerator Research Organization (KEK), Tsukuba (Japan); University of Tokyo (Japan). Kavli Institute for the Physics and Mathematics of the Universe (WPI); Japan Aerospace Exploration Agency (ISAS/JAXA), Sagamihara, Kanagawa (Japan). Institute of Space and Astronautical Science; Graduate University for Advanced Studies, SOKENDAI, Kanagawa (Japan)] (ORCID:0000000168308309), Jeong, Oliver [University of California, Berkeley, CA (United States)] (ORCID:0000000158937697), Kaneko, Daisuke [High Energy Accelerator Research Organization (KEK), Tsukuba (Japan)] (ORCID:000000033917086X), Keating, Brian [University of California, San Diego, CA (United States)] (ORCID:0000000331185514), Kusaka, Akito [University of Tokyo (Japan); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)] (ORCID:0009000496312451), Lee, Adrian [University of California, Berkeley, CA (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)] (ORCID:0000000331063218), Matsumura, Tomotake [University of Tokyo (Japan). Kavli Institute for the Physics and Mathematics of the Universe (WPI)] (ORCID:0000000190020686), Piccirillo, Lucio [University of Manchester (United Kingdom)] (ORCID:0000000178680841), Reichardt, Christian L. [University of Melbourne, Parkville, VIC (Australia)] (ORCID:0000000322269169), Sakaguri, Kana [University of Tokyo (Japan)] (ORCID:0000000156678118), Siritanasak, Praween [National Astronomical Research Institute of Thailand, Chiangmai (Thailand)] (ORCID:0000000168301537), Yamada, Kyohei [University of Tokyo (Japan)] (ORCID:0000000302212130). 2025-02-21. A Measurement of Atmospheric Circular Polarization with POLARBEAR. https://doi.org/10.3847/1538-4357%2Fada89b

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