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Hard X-ray observations of X-ray Nova Ophiuchi 1993 (GRS 1716-249) with GRANAT/SIGMA
Gilfanov 1, 2,
Churazov 1, 2,
Sunyaev 1, 2,
Received 5 May 1997 / Accepted 20 October 1997
The results of observations of X-ray Nova Ophiuchi 1993 (GRS 1716-249) in the hard X-ray/low -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 2-300 keV 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 0.2 Hz), typical for black hole candidates, a strong decline of the power density towards lower frequencies was found at Hz. This behavior of the PDS differs from the PDS observed for Cyg X-1 and resembles those observed for X-ray Nova Per 1992.
Key words: accretion disks black hole physics gamma-rays: observations X-rays: stars
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© European Southern Observatory (ESO) 1998
Online publication: February 16, 1998