First Ever Measurement of Quiet Sun Magnetic Field at Higher Coronal Heights Using Spectro-Polarimetric Radio Observation with SKA Precursor

Magnetic field couples the solar interior to the solar atmosphere, known as the corona. The coronal magnetic field is one of the crucial parameters which determines the coronal structures and regulates the space weather phenomena. Measuring the magnetic field at middle and higher coronal heights is an extremely difficult problem. It is particularly more challenging for the quiet solar corona, where the magnetic field strength is small. To date, there is no single measurement technique available to measure the quiet coronal magnetic field at middle and higher coronal magnetic fields. Theoretically, it is possible to measure the quiet Sun coronal magnetic field using very small (<1 %) induced circular polarization of thermal emission at low radio frequencies, which is not detected to date. With the newly developed precise polarization calibration of the solar observations done with the Murchison Widefield Array, a future Square Kilometer Array (SKA) precursor, we have brought down the instrumental polarization <1 %. This precise calibration allows us to detect the induced circular polarization from the quiet Sun for the first time. We have measured the magnetic field strength of the quiet solar corona using this method. We anticipate this method will provide good constraints to the different magnetic field extrapolation methods used largely for coronal magnetic field estimation.