RADIO IMAGING OBSERVATIONS OF THE EVOLUTION OF THERMAL AND NONTHERMALSOURCES 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 th ermal sources were located near the top of an arcade-like soft X-ray s tructure observed by the Yohkoh satellite, while a nonthermal source w as observed near the foot points of the arcade-like structure. During the early phase of the burst, an elongated structure was observed conn ecting one of the thermal sources and the nonthermal source. The elong ation started from the location of the nonthermal source and gradually progressed to the thermal source placed just radially above the nonth ermal 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 stru cture is an indication of chromospheric evaporation by radio imaging o bservations. The energetics of the thermal and nonthermal sources was analyzed using the radio and soft X-rav data. We suggest that a contin uous supply of accelerated electrons for about 1000 s can maintain the hot plasma observed at the foot points of the loop.