Mitigating Gain Calibration Errors in Epoch of Reionisation Observations with SKA1-Low

This research investigates the impact of residual extragalactic foregrounds arising from gain calibration errors on the efficacy of foreground mitigation strategies for Epoch of Reionisation (EoR) observations with SKA1-Low. The study uses an end-to-end pipeline $\textsc{21cmE2E}$ to simulate a realistic sky model and telescope configuration within the 138-146 MHz frequency range. A hybrid mitigation technique is introduced that combines the foreground removal techniques, Gaussian process regression and principal component analysis, with foreground avoidance. The results indicate that recovery of the HI signal within 2σ is possible for calibration gain error of ≤ 1% with minimal loss of power spectrum sensitivity over the scale range 0.05 ≤ k ≤ 0.5 Mpc$^{-1}$. The study finds that gain calibration errors beyond this threshold lead to signal suppression on large scales due to the loss of spectral smoothness of the residual foreground. The work offers a comparative assessment of three foreground mitigation strategies, removal, avoidance, and a hybrid approach.

The demonstration of the effectiveness of a hybrid foreground mitigation technique for SKA1-Low observations is a significant contribution. The ability to tolerate higher gain calibration errors simplifies observational requirements. The comparative assessment of different foreground mitigation strategies provides valuable guidance for future EoR observations.

Future research should focus on further optimizing the hybrid mitigation technique and exploring alternative approaches to foreground mitigation. Further investigation into the impact of gain calibration errors on the recovery of astrophysical parameters is crucial. This research contributes to the ongoing effort to detect the 21-cm signal from the Epoch of Reionisation and understand the Cosmic Dawn.

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