Precision Calibration of Radio Interferometers Using Redundant Baselines

TL;DR

This paper improves calibration methods for broadband radio interferometers with redundant baselines, addressing errors and biases to enhance sensitivity for 21 cm cosmology observations.

Contribution

It develops a unified calibration framework that accounts for deviations from perfect redundancy and coplanarity, reducing biases in redundant calibration schemes.

Findings

Simulations reveal errors and biases in existing redundant calibration methods.

A new formalism incorporates both redundant and point source calibration techniques.

Biases can be effectively eliminated with the proposed calibration approach.

Abstract

Growing interest in 21 cm tomography has led to the design and construction of broadband radio interferometers with low noise, moderate angular resolution, high spectral resolution, and wide fields of view. With characteristics somewhat different from traditional radio instruments, these interferometers may require new calibration techniques in order to reach their design sensitivities. Self-calibration or redundant calibration techniques that allow an instrument to be calibrated off complicated sky emission structures are ideal. In particular, the large number of redundant baselines possessed by these new instruments makes redundant calibration an especially attractive option. In this paper, we explore the errors and biases in existing redundant calibration schemes through simulations, and show how statistical biases can be eliminated. We also develop a general calibration formalism that includes both redundant baseline methods and basic point source calibration methods as special cases, and show how slight deviations from perfect redundancy and coplanarity can be taken into account.