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