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Astron. Astrophys. 339, 483-488 (1998)

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RXTE broad band observations of X-ray Nova XTE J1755-324

M. Revnivtsev * 1, M. Gilfanov 2, 1 and E. Churazov 2, 1

1 Space Research Institute, Russian Academy of Sciences Profsoyuznaya 84/32, Moscow 117810, Russia
2 Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Strasse 1, D-85740 Garching bei München, Germany

Received 27 April 1998 / Accepted 3 September 1998

Abstract

The properties of X-ray Nova XTE J1755-324, observed with the RXTE observatory in 1997 are reported. The lightcurve of the source was typical for X-ray Novae, except for somewhat shorter decay time scale and the time elapsed between the primary and subsequent secondary and tertiary outbursts. At the peak of the lightcurve the source had a two-component spectrum, typical for the bright X-ray Novae, with a characteristic disk blackbody temperature [FORMULA] keV and a photon index of the hard power law tail [FORMULA] 2.0. The peak luminosity can be roughly estimated as [FORMULA] erg/s (0.1-100 keV, assuming 8.5 kpc distance). A notable and peculiar feature of the spectral evolution of the source was a short, [FORMULA] days long, episode of increased hardness, occurred shortly before the tertiary maximum of the light curve. During the last RXTE pointed observations [FORMULA] days after the primary outburst the source has been found in the hard spectral state with a luminosity [FORMULA]few[FORMULA] erg/s. The overall pattern of the temporal and spectral evolution of XTE J1755-324 resembles in general that of "canonical" X-ray Novae (e.g. Nova Muscae 1991) and suggests that the compact object in the binary system is a black hole.

Key words: accretion, accretion disks – black hole physics – gamma-rays: observations – stars: individual: XTE J1755-324 – X-rays: stars

* visiting Max-Plank-Institut für Astrophysik

Send offprint requests to: M. Revnivtsev

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© European Southern Observatory (ESO) 1998

Online publication: October 21, 1998
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