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.