The BICEP3 and BICEP Array polarimeters are small-aperture refracting telescopes located at the South Pole designed to measure primordial gravitational wave signatures in the Cosmic Microwave Background (CMB) polarization, predicted by inflation. Constraining the inflationary signal requires not only excellent sensitivity, but also careful control of instrumental systematics. Both instruments use antenna-coupled orthogonally polarized detector pairs, and the polarized sky signal is reconstructed by taking the difference in each detector pair. As a result, the differential response between detectors within a pair becomes an important systematic effect we must control. Additionally, mapping the intensity and polarization response in regions away from the main beam can inform how sidelobe levels affect CMB measurements. Extensive calibration measurements are taken in situ every austral summer for control of instrumental systematics and instrument characterisation. In this work, we detail the set of beam calibration measurements that we conduct on the BICEP receivers, from deep measurements of main beam response to polarized beam response and sidelobe mapping. We discuss the impact of these measurements for instrumental systematics studies and design choices for future CMB receivers.
Measurements of B-mode polarization in the cosmic microwave background (CMB) sourced from primordial gravitational waves would provide information on the energy scale of inflation and its potential form. To achieve these goals, one must carefully characterize the Galactic foregrounds, which can be distinguished from the CMB by conducting measurements at multiple frequencies.
BICEP Array (BA) is the latest generation multi-frequency instrument of the BICEP/Keck program, which specifically targets degree-scale primordial B-modes in the CMB. In its final configuration, BA will consist of four small-aperture receivers, spanning six different frequency bands. The BA4 receiver is designed to characterize Galactic dust at 220/270 GHz. This receiver is currently undergoing commissioning at Stanford and is scheduled to deploy to the South Pole during the 2024-2025 austral summer. Here, we will provide an overview of this high frequency receiver, discussing the integration status and test results as it is being commissioned.
We summarize the technical specifications of TIME, the Tomographic Ionized-carbon Mapping Experiment, which is designed to probe the structure and evolution of the universe by using line intensity mapping to measure carbon monoxide (CO) and ionized carbon ([C ii]) with a mm-wavelength grating spectrometer. We present detector count, spectral coverage and resolution, and give an update on the current status of the project. TIME was installed at the Arizona Radio Observatory 12 m telescope in 2019 and returned for further engineering, commissioning, and observing in 2022. Data taken during the 2022 season demonstrate the ability of TIME to compensate for field rotation through the use of a K-mirror system, as well as spectro-imaging functionality broadly in line with expectations given the current state of the instrument. TIME will return to ARO for science observations for the Winter 2024 season. We discuss hardware and software updates and preliminary data analysis in preparation for science scans.
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