Long duration very soft X-ray flares

Using the RF15-I X-ray photometer aboard the INTERBALL-Tail satellite, we have identified a class of very soft, low intensity and long duration flares. They have decay time of the order of hours, low GOES class (similar toA or similar toB) and usually no detectable emission above 10 keV. We used YOHKOH Soft X-ray Telescope images to search for the sources of these events. We have found that, similarly to bigger flares, there is a large diversity in the morphology of these small events, including arcades of loops, interacting loop systems, and in one case a sigmoid. Many of these sources are observed at the limb and they may be a part of the larger structures hidden behind the solar disk. In this paper we present the morphology and investigate the physical parameters of three selected events. (C) 2002 Published by Elsevier Science Ltd on behalf of COSPAR.