BICEP / Keck XV: The BICEP3 CMB Polarimeter and the First Three Year Data Set

TL;DR

This paper presents the design, technological innovations, and three-year observational results of the BICEP3 CMB polarimeter, achieving the deepest polarization map at 95GHz over 585 square degrees.

Contribution

It introduces new technologies for CMB observation and provides the first three-year data set with unprecedented polarization map depth at 95GHz.

Findings

Achieved a polarization map depth of 2.8 μK-arcmin.

Demonstrated new optical and sensor technologies enabling higher throughput.

Collected the deepest CMB polarization data at 95GHz to date.

Abstract

We report on the design and performance of the BICEP3 instrument and its first three-year data set collected from 2016 to 2018. BICEP3 is a 52cm aperture, refracting telescope designed to observe the polarization of the cosmic microwave background (CMB) on degree angular scales at 95GHz. It started science observation at the South Pole in 2016 with 2400 antenna-coupled transition-edge sensor (TES) bolometers. The receiver first demonstrated new technologies such as large-diameter alumina optics, Zotefoam infrared filters, and flux-activated SQUIDs, allowing $\sim 10\times$ higher optical throughput compared to the Keck design. BICEP3 achieved instrument noise-equivalent temperatures of 9.2, 6.8 and 7.1$\mu\text{K}_{\text{CMB}}\sqrt{\text{s}}$ and reached Stokes $Q$ and $U$ map depths of 5.9, 4.4 and 4.4$\mu$K-arcmin in 2016, 2017 and 2018, respectively. The combined three-year data set achieved a polarization map depth of 2.8$\mu$K-arcmin over an effective area of 585 square degrees, which is the deepest CMB polarization map made to date at 95GHz.