A purely coronal hard X-ray event

Abstract

OSO 7 observations of a hard X-ray event of coronal origin are described. This event had a duration of more than 42 min as well as an abnormally large hard/soft ratio and apparently occurred after the disappearance of a bright coronal streamer. This gradual hard X-ray event is tentatively associated with open field lines extending well above the closed loop structures that participated in the originating flare. It is noted that a gradual hardening of the hard X-ray spectral distribution occurred during the event. Physical conditions in the source are considered, and the results are compared with observations of other hard X-ray events associated with flares.