A Python-Based Peeling Framework for Radio Interferometry: Application to uGMRT 650MHz Imaging

TL;DR

This paper introduces a Python-based direction-dependent calibration and peeling framework for radio interferometry, improving image quality and faint-source detection in uGMRT 650MHz imaging.

Contribution

The authors develop and demonstrate a CASA-compatible Python framework for subtracting bright sources and reducing artifacts in radio interferometric images.

Findings

Significantly flattened backgrounds and improved image fidelity.

Enhanced faint-source detectability and increased sensitivity.

Systematic reduction of background noise with multiple bright sources.

Abstract

Modern radio interferometric arrays offer high sensitivity, wide fields of view, and broad frequency coverage, but also pose significant data calibration challenges. Standard direction-independent calibration is insufficient to correct direction-dependent effects, such as ionospheric phase distortions and primary beam variations, which produce strong artifacts around bright sources and limit achievable image dynamic range. Built on standard CASA tasks, we present a Python-based direction-dependent calibration and peeling framework, demonstrated using radio continuum imaging data from the upgraded Giant Metrewave Radio Telescope (uGMRT). The framework efficiently subtracts bright-source models and suppresses their associated direction-dependent artifacts, producing significantly flattened backgrounds and improving image fidelity and faint-source detectability. We further introduce an optimized ``model-restoration'' strategy that mitigates direction-dependent artifacts while preserving the flux densities and morphologies of bright sources that are themselves of scientific interest. For fields containing multiple bright sources, sequential application of the framework systematically reduces background noise, thereby increasing sensitivity and faint-source detectability. The framework is Python-based, CASA-compatible, and can be readily applied to other mid- and low-frequency interferometric arrays. The code is publicly released with this paper.