Maximum entropy method for phase-unstable aperture synthesis

Abstract

An application of the Maximum Entropy Method (MEM) to the closure data is described. It is shown that although the basic principle of the method is to obtain a brightness distribution which has highest entropy, the closure phases play a prominent role in giving the correct reconstruction, especially when the distributions are complex and the measurement errors are large. The method gives faithful reconstruction for the observed random phase error of up to 150 deg. The method can be used as an alternative to the routinely used 'self-calibration' technique to improve the astronomical images obtained from the phase unstable interferometers. For large fields of view when, due to repetitive use of CLEAN, the 'self-calibration' method becomes time consuming, MEM with closure phase may have a computational advantage. For extended sources, as the performance of CLEAN deteriorates MEM could be superior to the self-calibration.