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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] -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] 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)

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© European Southern Observatory (ESO) 1998

Online publication: February 16, 1998
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