Low-frequency radio observations of coronal magnetic fields

Abstract

We report observations of circularly polarized noise storm emission from the solar corona at 77 and 109MHz during the period 11–18 August 2006 (Carrington Rotation 2046) with the recently commissioned East-West one-dimensional radio polarimeter at the Gauribidanur observatory, near Bangalore. Two-dimensional imaging observations at 77MHz around the same epoch with the radioheliograph at the observatory revealed that the radio source was associated with active region AR 10904 and co-rotated with it. The radial distance of the corresponding 77MHz plasma level derived independently from the observed rotation was about 1.1 R ⊙. The average magnetic field value that follows from the observed circularly polarized emission at this plasma level and radial distance is about 4G.