External Calibrator in Global Signal Experiment for Detection of the Epoch of Reionization

TL;DR

This paper explores the use of external calibrators, including celestial sources, in a 21 cm experiment to improve detection of the epoch of reionization by reducing instrumental and environmental effects.

Contribution

It proposes a novel external calibration approach and discusses observational strategies, highlighting the potential of Galactic diffuse emission as an effective calibrator.

Findings

External calibrators can reduce instrumental effects in EoR experiments.

Galactic diffuse emission's diurnal motion is a promising external calibrator.

Design of underground antenna system minimizes environmental interference.

Abstract

We present a conceptual design study of external calibrators in the 21 cm experiment towards detecting the globally averaged radiation of the epoch of reionization (EoR). Employment of external calibrator instead of internal calibrator commonly used in current EoR experiments allows to remove instrumental effects such as beam pattern, receiver gain and instability of the system if the conventional three-position switch measurements are implemented in a short time interval. Furthermore, in the new design the antenna system is placed in an underground anechoic chamber with an open/closing ceiling to maximally reduce the environmental effect such as RFI and ground radiation/reflection. It appears that three of the four external calibrators proposed in this paper, including two indoor artificial transmitters and one outdoor celestial radiation (the Galactic polarization), fail to meet our purpose. Diurnal motion of the Galactic diffuse emission turns to be the most possible source as an external calibrator, for which we have discussed the observational strategy and the algorithm of extracting the EoR signal.