Bayesian Data Analysis for Sky-averaged 21-cm Experiments in the Presence of Ionospheric Effects

TL;DR

This paper investigates how ionospheric effects impact the detection of the 21-cm cosmological signal, emphasizing the importance of accounting for time-varying ionospheric conditions to improve detection accuracy.

Contribution

It introduces a method to incorporate time-varying ionospheric effects into 21-cm data analysis and demonstrates how adaptive beam configurations enhance detection significance.

Findings

More than 5% error in ionospheric parameters reduces detection evidence.

Constant beam assumptions lower detection significance with more data.

Time-varying beam adjustments improve detection confidence.

Abstract

The ionosphere introduces chromatic distortions on low frequency radio waves, and thus poses a hurdle for 21-cm cosmology. In this paper we introduce time-varying chromatic ionospheric effects on simulated antenna temperature data of a global 21-cm data analysis pipeline, and try to detect the injected global signal. We demonstrate that given turbulent ionospheric conditions, more than 5\% error in our knowledge of the ionospheric parameters could lead to comparatively low evidence and high root-mean-square error (RMSE), suggesting a false or null detection. When using a constant antenna beam for cases that include data at different times, the significance of the detection lowers as the number of time samples increases. It is also shown that for observations that include data at different times, readjusting beam configurations according to the time-varying ionospheric conditions should greatly improve the significance of a detection, yielding higher evidences and lower RMSE, and that it is a necessary procedure for a successful detection when the ionospheric conditions are not ideal.