1998A&A...331..557R

The results of observations of X-ray Nova Ophiuchi 1993 (GRS 1716-249) in the hard X-ray/low γ-ray energy domain with the SIGMA telescope aboard the GRANAT observatory are reported. The hard X-ray emission from the source has been observed by SIGMA during the bright flare in 1993 and one year later-during the reappearance of the source in 1994. The SIGMA data combined with results of quasi simultaneous TTM (MIR-KVANT) observations, give a possibility to study the spectral behavior of the source in the 2-300eV energy band. Both in 1993 and 1994 the broad-band spectrum of GRS 1716-249 was quite similar to the low (hard) state spectrum of Cyg X-1, although subtle spectral variations, possibly correlated with the luminosity, were clearly detected. The results of timing analysis are also presented. Along with a turnover of the power density spectrum at high frequencies (above 0.2Hz), typical for black hole candidates, a strong decline of the power density towards lower frequencies was found at ν<0.01Hz. This behavior of the PDS differs from the PDS observed for Cyg X-1 and resembles those observed for X-ray Nova Per 1992.