Abstract

A purely polarized bright radio source was found at 17 GHz by the Nobeyama Radioheliograph. This source was associated with a large sunspot. The source structure of this S-component was resolved due to high spatial resolution of the radioheliograph. A soft X-ray image of this active region taken by Yohkoh Satellite shows no counterpart for the radio source. Emission mechanism of the radio source is identified as gyroresonance. Magnetic field of the sunspot was measured by the Haleakala Vector Magnetograph at Mees Solar Observatory. The field strength at the half power level of the radio source was 2000 gauss at the photospheric level. This corresponds to the third harmonic layer. A bright soft X-ray loop, whose footpoint is at the penumbra of the large sunspot, can also be seen in the radio map. This loop is strongly curved, to form a part of a spiral, which reflects strong electric current. Vector magnetogram shows strong rotation of the transverse field in the sunspot, which also corresponds to strong electric current. Due to this current and also to the density and the temperature enhancement near the X-ray loop, the radio peak is shifted toward the loop and has no dip.