The spectra of nova MUSCAE 1991 between 3 keV and 1 MeV observed with GRANAT.

Attention is given to the GRANAT observations of Nova Muscae (GRS1124-684), spanned over a year, which revealed the source in three apparently different spectral states, corresponding to different epochs of the soft X-ray light curve: a spectrum with two distinct components (soft, below about 8 keV, and hard power-law tail with a slope of about 2.5, detected up to about 300 keV); a soft spectrum (without hard power law tail); and a hard power law spectrum with a slope of about 2.2. Thus, while the 3-300 keV luminosity decreased by more than an order of magnitude, the source passed through all the spectral states known for galactic black hole candidates. On January 20-21, 1991 the SIGMA telescope aboard GRANAT detected a relatively narrow variable emission line near 500 keV with a net flux of about 0.006 phot/s sq cm, most probably due to positron annihilation occurring in the source.