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    PR # 31516                                                                   
     GRS 1758-258 is one of the two strongest emitters at E>100 keV near t       
     he Galactic Center. As its 'twin' source 1E1740.7-2942, it might be r       
     elated to the 511 keV line  observed from this direction.  Using simu       
     ltaneous ROSAT and SIGMA data we have found evidence for a soft exces       
     s in  its spectrum, supporting the idea that GRS1758-258 is a black h       
     ole candidate. ASCA will allow the first detailed spectral investigat       
     ion of this source in the 1-10 keV range,  where previous observation       
     s suffered from the limitations of non-imaging instruments.  The conf       
     irmation and study of the soft excess, the detection of spectral vari       
     ability,  and the investigation of Fe features in the 6-8 keV range w       
     ould greatly improve  our understanding of this very peculiar radio,        
    X and gamma-ray source.                                                      
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