An automated, self-calibration-based pipeline for high-fidelity solar imaging with LOFAR: SIMPL

¹ National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, S. P. Pune University Campus, Pune 411007, India
² ASTRON – The Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
³ NASA Jack Eddy Fellow, University Corporation for Atmospheric Research, 3090 Center Green Dr, Boulder, CO 80301, USA
⁴ The Johns Hopkins University Applied Physics Laboratory, 11001 Johns Hopkins Rd, Laurel 20723, USA

^⋆ Corresponding author: sohamd943@gmail.com

Received: 14 August 2025
Accepted: 22 September 2025

Abstract

Context. The LOw Frequency ARray (LOFAR) is capable of imaging spectroscopy of the Sun in the 10–240 MHz frequency range, with high spectral, temporal, and spatial resolution. However, the complex and rapidly varying nature of solar radio emission – spanning several orders of magnitude in brightness and further exacerbated by the strong ionospheric phase distortions during daytime observations, poses major challenges for calibration, imaging, and automation.

Aims. We aim to develop a fully automated, high-fidelity imaging pipeline optimised for LOFAR solar observations, capable of handling the intrinsic variability of solar emission and producing science-ready images with minimal human intervention.

Methods. We have built the Solar Imaging Pipeline for LOFAR (SIMPL), which integrates excision of radio-frequency interference (RFI) for the solar-specific scenarios, calibration strategies, and self-calibration. At present, SIMPL processes data from the LOFAR core stations and produces total-intensity solar images, with ongoing developments aimed at enabling full polarimetric imaging and incorporating increasingly distant antennas. The pipeline is designed to enable scalable and uniform processing of large archival datasets.

Results. In terms of performance, SIMPL achieves more than an order of magnitude improvement in imaging dynamic range compared with previous efforts and reliably produces high-quality spectroscopic snapshot images. It has been tested across a wide range of solar conditions. It is currently being employed to process a decade of LOFAR solar observations, providing science-ready Flexible Image Transport System (FITS) images for the community and enabling both comprehensive and novel studies of solar radio phenomena, ranging from quiet Sun emission and faint non-thermal features to active regions and their associated dynamic events, such as transient bursts.