Tackling the Unique Challenges of Low-frequency Solar Polarimetry with the Square Kilometre Array Low Precursor: Pipeline Implementation

Devojyoti Kansabanik, Apurba Bera, Divya Oberoi, Surajit Mondal

Submitted on 14 September 2022


The dynamics and the structure of the solar corona are determined by its magnetic field. Measuring coronal magnetic fields is, however, extremely hard. The polarization of the low-frequency radio emissions is one of the few observational probes of magnetic fields in the mid and high corona. Polarimetric calibration and imaging of the Sun at these frequencies is challenging. The brightness temperature and degree of polarization of the low-frequency solar radio emissions can vary by several orders of magnitude. These emissions also show dramatic spectral and temporal variations. Hence, to study these radio emissions, one needs high dynamic range spectro-polarimetric snapshot imaging. The Murchison Widefield Array (MWA), a Square Kilometre Array (SKA) precursor, is exceptionally well-suited for this purpose. Calibration and imaging of solar data to extract this information are, however, significant challenges in themselves - requiring a deep understanding of the instrument, capable sophisticated algorithms, and their reliable implementation. To meet these challenges we have developed an unsupervised and robust polarization calibration and imaging software pipeline. Here we present the architecture and some implementation details of this pipeline. It delivers high-fidelity and high-dynamic-range full polarimetric solar radio images at high spectro-temporal resolutions. We expect this pipeline to enable exciting new science with instruments like the MWA. We also hope that by not requiring a significant prior background in radio interferometric imaging, this pipeline will encourage wider use of radio imaging data in the larger solar physics community. The algorithm implemented here can easily be adapted for future arrays like the SKA.


Comment: 22 pages, 11 figures, 1 table. Submitted to the Astrophysical Journal

Subjects: Astrophysics - Solar and Stellar Astrophysics; Astrophysics - Instrumentation and Methods for Astrophysics