Abstract

On 18 July 2002, an M-class flare were observed with RHESSI and the Nobeyama Radio Heliograph (NoRH). We compared the hard X-ray (HXR) images in the energy range above 30 keV and 17 GHz radio maps taken during the impulsive phase. Two HXR sources were observed and they were located at the two ends of a long (~ 20000 km) loop structure, which was observed with TRACE in the later phase. The stronger HXR source was located at the northern end of the loop and the weaker one was at the southern end. On the other hand, a single radio source was observed in 17 Hz and it was located at the site of the southern (or weaker) HXR source. In EUV images, a few small ( < 5000 km) loops were observed near the northern (stronger) HXR source. These observations suggest that the electron acceleration occurred at the interaction site between the long loop and the small loops, and then they precipitated along the two loops. Such flares have been often observed with Yohkoh/HXT and NoRH in these ten years. Usually two radio emission sources and one HXR source have been observed. The main radio source is located at the same location as the HXR source and the remote radio source are located at the other end of the long loop where there is no HXR source. It is believed the main radio source and the HXR source include the emission from two footpoints of the small loop and a footpoint of the long loop due to the poor spatial resolutions of HXT and NoRH. In the case of the 18-July-2002 flare, most of observational facts are consistent to this scenario. However, the lack of radio emission at the northern region is much different from the characteristics of the same type of events which have been observed with HXT and NoRH. We focus our attention on this difference and confirm whether this flare can be explained by the simple loop-loop interaction model or not.