Low-frequency Observations of Polarized Emission from Long-lived Non-thermal Radio Sources in the Solar Corona

Abstract

We report observations of circularly polarized emission from the solar corona at 77 MHz during the periods 2006 August 11-18, 2006 August 23-29, and 2007 May 16-22 in the minimum phase between the sunspot cycles 23 and 24. The observations were carried out with the east-west one-dimensional radio polarimeter at the Gauribidanur observatory located about 100 km north of Bangalore. Two-dimensional imaging observations at 77 MHz during the same period with the radioheliograph at the same observatory revealed that the emission region co-rotated with the Sun during the three aforementioned periods. Their rotation rates, close to the central meridian on the Sun, are 4farcm6, 5farcm2, and 4farcm9 ± 0farcm5 per day, respectively. We derived the radial distance of the region from the above observed rotation rates and the corresponding values are ≈1.24 ± 0.03 R sun (2006 August 11-18), ≈1.40 ± 0.03 R sun (2006 August 23-29), and ≈1.32 ± 0.03 R sun (2007 May 16-22). The estimated lower limit for the magnetic field strength at the above radial distances and periods are ≈1.1, 0.6, and 0.9 G, respectively.