Hard X-ray and gamma-ray observations of an electron dominated event associated with an occulted solar flare

This paper reports hard X-ray (HXR) and gamma-ray (GR) observations of an i mpulsive electron-dominated event which occurred on 1991 June 30 at similar or equal to 0256 UT. This event is associated with an optical flare produc ed in an active region located behind the east solar limb. When observed fr om the earth's direction, it appears as a moderate HXR/GR burst but still s hows significant emission in the 10-100 MeV range. During most of the event , the photon spectrum exhibits a hardening above a break energy of 0.5 MeV and no significant GR line (GRL) emission is detected. When viewed from a l argely different direction, this impulsive event corresponds to one of the giant hares observed with ULYSSES. The main results of the present analysis are: (i) the HXR/GR emission observed from the earth's direction represents only a small fraction of the total X-ray emission; while the unocculted emissio n below 0.5 MeV is likely produced in the corona at heights greater than 10 (4) km the higher energy emission probably originates from thick target int eraction on the visible disk; (ii) although associated with an occulted optical flare, this event exhibit s at high energies spectral characteristics similar to what is observed for a disk electron dominated event; (iii) even if no significant GRL emission is detected, the observations can not exclude that a greater than or similar to 1MeV/nuc ion energy content c omparable to the greater than or similar to 20 keV electron content is prod uced in the flare; the comparable energy contents between electrons and ion s found for strong GRL flares and for one electron dominated event associat ed with a disk flare thus also holds for the unocculted part of this event.