Long duration very soft X-ray flares Original Research Article

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 (∼A or ∼B) 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.