Initial results from the solar flare X-ray observations with ulysses

Abstract

The Solar X-Ray/Cosmic Gamma-Ray Burst Experiment aboard the Ulysses spacecraft measures hard X-ray spectra in the nominal energy range 15-150 keV, which can be changed by ground command. Since the experiment turn-on on 11 November 1990, it has recorded hard X-ray emission from ~100 solar flares of GOES soft X-ray class > M and several hundred smaller flares. Some of these flares were also observed by comparable instruments aboard other interplanetary and near-Earth spacecraft such as Pioneer Venus Orbiter (PVO), Yohkoh and Compton Observatory (formerly GRO), thus providing a stereoscopic view of the hard X-ray sources in those flares. This paper presents a brief description of the Ulysses instrument and some early observational results.