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Astron. Astrophys. 342, 496-501 (1999)

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Spring, 1997 GRANAT/SIGMA observations of the Galactic Center:
discovery of the X-ray nova GRS 1737-31

S. Trudolyubov 1,2, E. Churazov 1,2, M. Gilfanov 1,2, M. Revnivtsev 1,2, R. Sunyaev 1,2, N. Khavenson 1, A. Dyachkov 1, I. Tserenin 1, M. Vargas 3, P. Goldoni 4, P. Laurent 4, J. Paul 4, E. Jourdain 5, J.-P. Roques 5, P. Mandrou 5 and G. Vedrenne 5

1 Space Research Institute, Russian Academy of Sciences Profsoyuznaya 84/32, 117810 Moscow, Russia
2 Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Strasse 1, D-85740 Garching bei München, Germany
3 INTEGRAL Science Data Centre, 16, chemin d'Ecogia, CH-1290 Versoix, Switzerland
4 CEA/DSM/DAPNIA/SAp, Centre d'Etudes de Saclay, F-91191 Gif-sur-Yvette, Cedex, France
5 Centre d'Etude Spatiale des Rayonnements (CNRS/UPS), 9, avenue du Colonel Roche, B.P. 4346, F-31028 Toulouse Cedex, France

Received 26 June 1998 / Accepted 12 November 1998

Abstract

The results of GRANAT /SIGMA hard X-ray observations of the Galactic center in March, 1997 are reported. One new source - GRS 1737-31 and two previously known sources - 1E 1740.7-2942 and GRO J1744-28 were detected. The spectral and temporal behavior of GRS 1737-31 suggests that this source may be a distant X-ray Nova and a black hole candidate.

The comparison of the hard X-ray transient detection rates by GRANAT /SIGMA and currently operating all-sky monitors (CGRO /BATSE, GRANAT /WATCH) leads to following conclusions regarding the spatial and luminosity distributions of the hard X-ray transients:

(i) the spatial distribution of X-ray Novae exhibits a concentration towards the Galactic Center similar to the distribution of the visible matter in the Galaxy. In particular, it is more concentrated than Galactic disk population.

(ii) if hard X-ray transients follow distribution of visible mass in the Galaxy then their peak luminosity in the 35-150 keV band is close to [FORMULA] erg s-1 with a relatively small scatter.

Key words: stars: individual: 1E 1740.7-2942 – stars: individual: GRO J1744-28 – stars: individual: GRS 1737-31 – stars: novae, cataclysmic variables – gamma rays: observations – X-rays: stars

Send offprint requests to: S.Trudolyubov (tsp@hea.iki.rssi.ru)

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© European Southern Observatory (ESO) 1999

Online publication: February 22, 1999
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