Name: Devojyoti Kansabanik
Affiliation: National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, Pune, India
Conference ID : ASI2022_40
Title : Towards measuring coronal magnetic field using high fidelity low-frequency spectro-polarimetric radio imaging with SKA precursor
Authors : Devojyoti Kansabanik, Divya Oberoi
Abstract Type: Poster
Abstract Category : Sun and the Solar System
Abstract : Magnetic field measurements at middle and higher coronal heights are challenging using conventional observations at visible or extreme ultra-violet wavelengths. Low-frequency radio wavelengths are ideal for probing higher coronal heights. Polarization properties of solar radio emissions are known to be a rich source of information about the emission mechanisms and coronal magnetic fields. Nonetheless, largely due to technical challenges, precise polarimetric solar observations at low radio frequencies have remained mostly beyond reach. The degree of polarization of solar radio emission varies dramatically over time, frequency, and also in morphology, depending on the emission mechanism. The radio bursts show moderate to high degrees of circular polarization, while the quiet sun thermal emissions show a very low degree of circular polarization (<1%). Once feasible, detection of this very low circular polarisation from quiet Sun thermal emission will be an important tool to measure quiet Sun coronal magnetic field. Simultaneous measurements of linear and circular polarisation from active emissions are important to understand the quasi-longitudinal and quasi-transverse propagation and will be a direct probe of the magnetic field geometry. Conventional view has been that the large differential coronal Faraday rotation will wipe out any solar linear polarization. We, however, find convincing detections of linear polarization in active solar emissions. Perhaps the most rewarding, and also challenging, will be the polarimetric observations of gyrosynchrotron emission from CME plasma, which will enable modeling the CME plasma parameters unambiguously at higher coronal heights. We are developing a radio interferometric calibration and imaging pipeline for snapshot spectro-polarimeteric solar imaging to enable the studies enumerated above and more. Here we summarise its current status and showcase some early science results. While this pipeline is optimized for the Murchison Widefield array, a Square Kilometer Array (SKA) precursor, it can be adapted for the SKA-Low and other upcoming solar arrays.