Abstract

We give an overview of the observations of long duration events (LDEs) as observed with the Nobeyama Radioheliograph. Images of LDEs at 17 GHz show not only the brightening of arcade loops, which also characterizes soft X-ray images, but also of their footpoints. The observations indicate that the brightening of arcade loops is due to free-free emission from the hot and dense thermal plasma and that the footpoint brightening, highly polarized, is due to gyroresonance emission from thermal plasma in strong magnetic field regions. Except during the initial part of some events, there is no hint of gyrosynchrotron emission, indicative of the absence of high-energy electrons in LDEs. The radio data provide temperature diagnostics of the arcade loops when compared with soft X-ray images, and information on the magnetic field structures through analyses of the polarization maps. These are discussed in this paper.