BEHAVIOR OF ACCELERATED ELECTRONS IN A SMALL IMPULSIVE SOLAR-FLARE ON1992 AUGUST 12

A GOES Cl.0-class impulsive flare was observed by the new Nobeyama Rad ioheliograph on 1992 August 12 with 1 s temporal and 10'' spatial reso lutions at 17 GHz. The radio flare consisted of an impulsive phase of approximately 20 s and a decay phase of approximately 90 s. Radio imag es showed double sources in the impulsive phase, whereas in the decay phase a single elongated source appeared which connected the double so urces. Soft X-ray images with Yohkoh/SXT show that the radio double so urces correspond to foot points of newly appearing coronal loops and t he single source was located at the top of one of the loops. The radio emission for both phases can be explained by gyrosynchrotron radiatio n from accelerated electrons. These loops began to brighten at their i ntersecting point approximately 1 min before the radio flare. All of t hese facts suggest that the reconnection of magnetic fields heated up the coronal loops and produced accelerated electrons, which ran throug h the loops, precipitated onto the foot points, and caused the radio f lare. Less than 1% of the electrons were mirrored at the foot points a nd trapped at the top of the loop. The lack of radio emission in the l oop top area during the impulsive phase implies that the accelerated e lectrons were highly beamed.