Calibration of detector time constant with a thermal source for the POLARBEAR-2A CMB polarization experiment

TL;DR

This paper presents a new calibration system for the POLARBEAR-2A experiment that accurately measures detector time constants to reduce polarization measurement bias in CMB observations.

Contribution

The paper introduces a novel calibrator system designed to precisely calibrate detector time constants for the POLARBEAR-2A CMB experiment.

Findings

Calibration system successfully measures detector time constants.

Preliminary results show improved accuracy in polarization angle measurement.

Calibration reduces bias caused by detector time constant uncertainties.

Abstract

The Simons Array (SA) project is a ground-based Cosmic Microwave Background (CMB) polarization experiment. The SA observes the sky using three telescopes, and POLARBEAR-2A (PB-2A) is the receiver system on the first telescope. For the ground-based experiment, atmospheric fluctuation is the primary noise source that could cause polarization leakage. In the PB-2A receiver system, a continuously rotating half-wave plate (HWP) is used to mitigate the polarization leakage. However, due to the rapid modulation of the polarization signal, the uncertainty in the time constant of the detector results in an uncertainty in the polarization angle. For PB-2A, the time constant of each bolometer needs to be calibrated at the sub-millisecond level to avoid introducing bias to the polarization signal. We have developed a new calibrator system that can be used to calibrate the time constants of the detectors. In this study, we present the design of the calibration system and the preliminary results of the time constant calibration for PB-2A.