Observing low elevation sky and the CMB Cold Spot with BICEP3 at the South Pole

TL;DR

BICEP3, a telescope at the South Pole, uses low-elevation observations to extend sky coverage, enabling detailed polarization measurements of the CMB, including the Cold Spot region, and detecting degree-scale E-modes with high confidence.

Contribution

This work introduces a low-elevation observation strategy with BICEP3 to enhance sky coverage and study polarization anomalies around the CMB Cold Spot.

Findings

Degree-scale E-modes measured with high signal-to-noise ratio.

Extended coverage of the Southern sky at low elevations.

Preliminary detection of polarization features near the CMB Cold Spot.

Abstract

BICEP3 is a 520 mm aperture on-axis refracting telescope at the South Pole, which observes the polarization of the cosmic microwave background (CMB) at 95 GHz to search for the B-mode signal from inflationary gravitational waves. In addition to this main target, we have developed a low-elevation observation strategy to extend coverage of the Southern sky at the South Pole, where BICEP3 can quickly achieve degree-scale E-mode measurements over a large area. An interesting E-mode measurement is probing a potential polarization anomaly around the CMB Cold Spot. During the austral summer seasons of 2018-19 and 2019-20, BICEP3 observed the sky with a flat mirror to redirect the beams to various low elevation ranges. The preliminary data analysis shows degree-scale E-modes measured with high signal-to-noise ratio.