1998A&A...339..483R

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 T_in∼0.8keV and a photon index of the hard power law tail α∼2.0. The peak luminosity can be roughly estimated as L∼10³⁸erg/s (0.1-100keV, assuming 8.5kpc distance). A notable and peculiar feature of the spectral evolution of the source was a short, ∼10days long, episode of increased hardness, occurred shortly before the tertiary maximum of the light curve. During the last RXTE pointed observations ∼100days after the primary outburst the source has been found in the hard spectral state with a luminosity ∼fewx10³⁶erg/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.