STEREOSCOPIC OBSERVATIONS OF SOLAR HARD X-RAY FLARES MADE BY ULYSSES AND YOHKOH

The Solar X-Ray/Cosmic Gamma-Ray Burst Experiment aboard the interplan etary spacecraft Ulysses has provided extensive observations of solar hard X-ray flares from a variety of angles with respect to the Sun-Ear th line. During the period 1991 October-1993 June, Ulysses observed 13 flares that were also observed by the X-ray instruments aboard the Ja panese satellite Yohkoh located near Earth. At least 12 flares were in full view of both the spacecraft. Eight flares, for which hard X-ray spectra were available, are examined to determine the directivity of t he 20-125 keV hard X-ray sources in solar flares. They include one fla re for which the view angles of Ulysses and Yohkoh were 80 degrees and 25 degrees, respectively. No evidence of systematic directivity was f ound within the uncertainty (a factor of similar to 2) of these measur ements. These and other observations of directivity at higher energies are consistent with a nearly isotropic distribution of energetic elec trons in most solar flares.