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Astron. Astrophys. 331, 557-563 (1998)
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Hard X-ray observations of X-ray Nova Ophiuchi 1993 (GRS 1716-249) with GRANAT/SIGMA
M. ,
Revnivtsev 1,
M. ,
Gilfanov 1, 2,
E. ,
Churazov 1, 2,
R. ,
Sunyaev 1, 2,
K. ,
Borozdin 1,
N. ,
Alexandrovich 1,
N. ,
Khavenson 1,
I. ,
Chulkov 1,
A. ,
Goldwurm 2,
J. ,
Ballet 2,
M. ,
Denis 2,
P. ,
Laurent 2,
J-P. ,
Roques 3,
V. ,
Borrel 3,
L. ,
Bouchet 3,
E. and
Jourdain 3
1 Space Research Institute, Russian Academy of Sciences
Profsoyuznaya 84/32, 117810 Moscow, Russia
2 Max-Planck-Institut für Astrophysik,
Karl-Schwarzschild-Str. 1, D-85740 Garching, Germany
3 CEA, Centre d'Etudes de Saclay Orme des Merisiers,
F-91191 Gif-sur-Yvette, Cedex, France
4 Centre d'Etude Spatiale des Rayonnements 9, avenue du
Colonel Roche, BP 4346, F-31029 Toulouse Cedex, France
Received 5 May 1997 / Accepted 20 October 1997
Abstract
The results of observations of X-ray Nova Ophiuchi 1993 (GRS
1716-249) in the hard X-ray/low ![[FORMULA]](img1.gif)
-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
![[FORMULA]](img2.gif)
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
Send offprint requests to: M. Revnivtsev(revnivtsev@hea.iki.rssi.ru)
© European Southern Observatory (ESO) 1998
Online publication: February 16, 1998
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