RADIO IMAGING OBSERVATIONS OF THE EVOLUTION OF THERMAL AND NONTHERMAL SOURCES DURING A GRADUAL SOLAR-BURST

With the Nobeyama Radioheliograph, evolution of thermal and nonthermal radio sources was observed during a gradual solar radio burst. Two thermal sources were located near the top of an arcade-like soft X-ray structure observed by the Yohkoh satellite, while a nonthermal source was observed near the foot points of the arcade-like structure. During the early phase of the burst, an elongated structure was observed connecting one of the thermal sources and the nonthermal source. The elongation started from the location of the nonthermal source and gradually progressed to the thermal source placed just radially above the nonthermal source with the velocity of about 170 km s-1. These observations imply that the thermal source and the nonthermal source are connected by a single magnetic loop. and that the elongation of the source structure is an indication of chromospheric evaporation by radio imaging observations. The energetics of the thermal and nonthermal sources was analyzed using the radio and soft X-rav data. We suggest that a continuous supply of accelerated electrons for about 1000 s can maintain the hot plasma observed at the foot points of the loop.