Calibration of CMB Telescopes with PROTOCALC

TL;DR

The paper introduces PROTOCALC, a highly accurate polarized calibrator source for CMB telescopes at 90 GHz, crucial for precise polarization measurements in cosmology.

Contribution

Development and first flight of PROTOCALC, a novel polarized calibrator with sub-degree polarization direction accuracy for CMB telescope calibration.

Findings

PROTOCALC successfully flew in May 2022.

It demonstrated promising calibration performance.

The polarization direction accuracy is better than 0.1 degrees.

Abstract

Cosmic Microwave Background experiments need to measure polarization properties of the incoming radiation very accurately to achieve their scientific goals. As a result of that, it is necessary to properly characterize these instruments. However, there are not natural sources that can be used for this purpose. For this reason, we developed the PROTOtype CALibrator for Cosmology, PROTOCALC, which is a calibrator source designed for the 90 GHz band of these telescopes. This source is purely polarized and the direction of the polarization vector is known with an accuracy better than 0.1 deg. This source flew for the first time in May 2022 showing promising result.