High resolution polarimetry of the Sun at 3.7 and 11.1 cm wavelengths

Abstract

The four Stokes parameters are presented for interferometric observations of the Sun at wavelengths of λ = 3.7 cm and λ = 11 cm with angular resolutions between 2.7 and 36.7 seconds of arc. An Hα solar flare of importance SN and type C has a radio wavelength (λ = 3.7 cm) size of 5 seconds of arc, a flux density of 0.3 × 10−22 W m−2 Hz−1, and a brightness temperature on the order of 107 K. The radio flare is 30% left circularly polarized at λ = 3.7 cm, 70% left circularly polarized at λ = 11 cm, and no detectable linear polarization was observed at either wavelength. During a forty hour observation of sunspot region McMath No 13926 no substantial variations in circular polarization were observed, whereas one hour prior to the eruption of a solar flare dramatic changes in circular polarization were observed. Small scale features whose angular sizes are on the order of five seconds of arc exhibit changes of circular polarization of up to 80%. At times other than those immediately preceding flare emission, the degree of circular polarization was the same at the two wavelengths but the sign was reversed. This situation can be explained if magnetic fields of intensityH ⩽ 1000 G and electron densities ofNe ⩾ 107 cm−3 are present.