The development of X-ray flare onsets near active region filaments

Skylab X-ray images of the early phases of six active region transient brightenings were compared with simultaneous H images to study the spatial relationships between filaments and the X-ray brightenings. When the X-ray loops were roughly perpendicular to the axes of the H filaments, the filaments did not disappear. X-ray loops which appeared nearly parallel to the filaments were generally associated with the disappearances of those filaments. It is suggested that the perpendicular loops correspond to the class I X-ray flares of Pallavicini et al. (1977) while the parallel loops are the early phases of their class II flares characterized in the decay phases by arcades of large loops with low energy densities. Both kinds of X-ray flares can be associated with impulsive phases.