ASCAObservations of the Galactic Bulge Hard X‐Ray Source GRS 1758−258

GRS 1758-258 is one of the few persistent hard X-ray emitters (E>100 keV) inthe Galaxy. Using the ASCA satellite, we have obtained the first detailed dataon GRS 1758-258 in the 1-10 keV range, where previous observations wereaffected by confusion problems caused by the nearby strong source GX5-1. Thespectrum is well described by a power law with photon index 1.7 without strongFe emission lines. A prominent soft excess, as observed with ROSAT when thehard X-ray flux was in a lower intensity state, was not detected. However, thepresence of a soft spectral component, accounting for at most 5% of the 0.1-300keV flux, cannot be excluded. The accurate measurement of interstellarabsorption (N_H=(1.5+-0.1) x 10^22 cm -2) corresponds to an optical extinctionwhich definitely excludes the presence of a massive companion.