Simultaneous ultraviolet line and hard X-ray bursts in the impulsive phase of solar flares

Abstract

Several fast impulsive phase solar flare bursts were observed by the Solar Maximum Mission instruments on 1980 November 8. The bursts were seen to be coincident in the O V 1371 A line formed at 2.5 x 10/sup 5/ K and in 25--300 keV X-rays, to within the resolution time of 1 s. This lack of time difference is inconsistent with models for these flares in which the hard X-rays are produced at the top of a loop, followed by the formation of a thermal conduction front which travels to the footpoint where a UV burst is produced by heating. Models in which both X-rays and UV radiation are produced at the footpoint, or an electron beam transmits energy between loop top and footpoint is less than 1 s, are allowed.