EDP Sciences
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Volume 433, Number 2, April II 2005
Page(s) 613 - 617
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:20042058

A&A 433, 613-617 (2005)
DOI: 10.1051/0004-6361:20042058

1E 1740.7-2942: Temporal and spectral evolution from INTEGRAL and RXTE observations

M. Del Santo1, A. Bazzano1, A. A. Zdziarski2, D. M. Smith3, N. Bezayiff3, R. Farinelli4, G. De Cesare1, P. Ubertini1, A. J. Bird5, M. Cadolle Bel6, F. Capitanio1, A. Goldwurm6, A. Malizia7, I. F. Mirabel6, L. Natalucci1 and C. Winkler8

1  Istituto di Astrofisica Spaziale e Fisica cosmica - CNR, via del Fosso del Cavaliere 100, 00133 Roma, Italy
    e-mail: melania.delsanto@rm.iasf.cnr.it
2  Nicolaus Copernicus Astronomical Center, Bartycka 18, 00-716 Warszawa, Poland
3  Department of Physics, University of California, Santa Cruz, Santa Cruz, CA 95064, USA
4  Dipartimento di Fisica, University of Ferrara, via del Paradiso 12, 44100 Ferrara, Italy
5  School of Physics and Astronomy, University of Southampton, SO17 1BJ, UK
6  CEA Saclay, DSM/DAPNIA/SAp (CNRS FRE 2591), 91191 Gif sur Yvette Cedex, France
7  IASF/CNR, sezione di Bologna, via P. Gobetti 101, 40129 Bologna, Italy
8  Research and Scientific Support Department of ESA, ESTEC, Postbus 299, 2200 AG Noordwijk, The Netherlands

(Received 23 September 2004 / Accepted 17 November 2004)

We present results of the monitoring of the black hole candidate 1E 1740.7-2942 with INTEGRAL, in combination with simultaneous observations by RXTE. We concentrate on broad-band spectra from INTEGRAL/IBIS and RXTE/PCA instruments. During our observations, the source spent most of its time in the canonical low/hard state with the measured flux variation within a factor of two. In 2003 September the flux started to decline and in 2004 February it was below the sensitivity level of the INTEGRAL and RXTE instruments. Notably, during the decline phase the spectrum changed, becoming soft and typical of black-hole binaries in the intermediate/soft state.

Key words: gamma rays: observations -- radiation mechanisms: non-thermal -- stars: individual: 1E 1740.7-2942 -- X-rays: binaries -- black hole physics

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