Calibration of the EDGES High-Band Receiver to Observe the Global 21-cm Signature from the Epoch of Reionization

TL;DR

This paper details the calibration process of the EDGES High-Band receiver, aiming to detect the 21-cm signal from the Epoch of Reionization, and discusses how calibration uncertainties impact the residual noise levels.

Contribution

It presents a calibration strategy for the EDGES High-Band receiver and quantifies how uncertainties affect the residuals in 21-cm signal detection.

Findings

Most calibration uncertainties yield residuals of 1 mK or less at 95% confidence.

Current reflection coefficient uncertainties can cause residuals up to 20 mK.

Improving reflection measurements and impedance matching can reduce residuals.

Abstract

The EDGES High-Band experiment aims to detect the sky-average brightness temperature of the $21$-cm signal from the Epoch of Reionization (EoR) in the redshift range $14.8 \gtrsim z \gtrsim 6.5$. To probe this redshifted signal, EDGES High-Band conducts single-antenna measurements in the frequency range $90-190$ MHz from the Murchison Radio-astronomy Observatory in Western Australia. In this paper, we describe the current strategy for calibration of the EDGES High-Band receiver and report calibration results for the instrument used in the $2015-2016$ observational campaign. We propagate uncertainties in the receiver calibration measurements to the antenna temperature using a Monte Carlo approach. We define a performance objective of $1$~mK residual RMS after modeling foreground subtraction from a fiducial temperature spectrum using a five-term polynomial. Most of the calibration uncertainties yield residuals of $1$~mK or less at $95\%$ confidence. However, current uncertainties in the antenna and receiver reflection coefficients can lead to residuals of up to $20$ mK even in low-foreground sky regions. These dominant residuals could be reduced by 1) improving the accuracy in reflection measurements, especially their phase 2) improving the impedance match at the antenna-receiver interface, and 3) decreasing the changes with frequency of the antenna reflection phase.