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

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Abstract
GRS 1758-258 is one of the few persistent hard X-ray emitters (E > 100 keV) in the Galaxy. Using the ASCA satellite, we have obtained the first detailed data on GRS 1758-258 in the 1-10 keV range, where previous observations were affected by confusion problems caused by the nearby strong source GX 5-1. The spectrum is well described by a power law with photon index 1.7 without strong Fe emission lines. A prominent soft excess, as observed with ROSAT when the hard X-ray flux was in a lower intensity state, was not detected. However, the presence of a soft spectral component, accounting for at most 5% of the 0.1-300 keV flux, cannot be excluded. The accurate measurement of interstellar absorption [NH = (1.5 ± 0.1) × 1022 cm-2] corresponds to an optical extinction that definitely excludes the presence of a massive companion.
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