THE STRUCTURE OF THE CORONAL SOFT-X-RAY SOURCE ASSOCIATED WITH THE DARK FILAMENT DISAPPEARANCE OF 1991 SEPTEMBER 28 USING THE YOHKOH SOFT-X-RAY TELESCOPE

The internal structure of an X-ray emitting elongated object appearing in association with Halpha-dark filament disappearance of 1991 September 28 was analyzed with the help of a fine-structure enhancing technique. We present a description of the soft X-ray structures and their evolution, while focusing on the central, brightest part of the structure, which is also the most difficult to resolve. We start with the idea of applying the standard "eruption-reconnection" models of Halpha double-ribbon flares with filament disappearences in order to explain this event as the appearence of an arcade of loops across the initial dark filament position, with a row of hot spots at reconnection sites along the loop tops. Our study of the Yohkoh Soft X-ray images, including their fine-structure enhancement, the making of an accurately aligned movie, and a preliminary comparison with Halpha data, however, has led us to question the applicability of these models to this type of event. It seems, rather, that much of the bright structure comprises heated pre-existing loops, which interact where they cross each other in a complex "knot" at the northern end of the disappearing dark filament. The bright part turns out to comprise highly sheared loops, perhaps being pushed up by the slowly rising axial field of the dark filament, which is, however, contained under the arcade, rather than having broken through it. We conclude that there is a strong possibility that much of the dark filament mass remains in the heated unwinding axial field and briefly discuss the theoretical implications.