Abstract

A GOES C1.0-class impulsive flare was observed by the new Nobeyama Radioheliograph on 1992 August 12 with 1 sec temporal and 10 sec spatial resolutions at 17 GHz. The radio flare consisted of an impulsive phase of approximately 20 sec and a decay phase of approximately 90 sec. Radio images showed double sources in the impulsive phase, whereas in the decay phase a single elongated source appeared which connected the double sources. Soft X-ray images with Yohkoh Soft X-ray Telescope (SXT) show that the radio double sources correspond to foot points of newly appearing coronal loops and the single source was located at the top of one of the loops. The radio emission for both phases can be explained by gyrosynchrotron radiation from accelerated electrons. These loops began to brighten at their intersecting point approximately 1 min before the radio flare. All of these facts suggest that the reconnection of magnetic fields heated up the coronal loops and produced accelerated electrons, which ran through the loops, precipitated onto the foot points, and caused the radio flare. Less than 1% of the electrons were mirrored at the foot points and trapped at the top of the loop. The lack of radio emission in the loop top area during the impulsive phase implies that the accelerated electrons were highly beamed.