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Astronomy and Astrophysics 446 (2006) 591-602
The broad-band spectrum of Cygnus X-1 measured by INTEGRAL
M. Cadolle Bel1, 2, P. Sizun2, A. Goldwurm1, 2, J. Rodriguez2, 3, P. Laurent1, 2, A. A. Zdziarski4, L. Foschini5, P. Goldoni1, 2, C. Gouiffès2, J. Malzac6, E. Jourdain6, J.-P. Roques6
INTEGRAL Collaboration(s)

The INTEGRAL satellite extensively observed the black hole binary Cygnus X-1 from 2002 November to 2004 November during calibration, open time and core program (Galactic Plane Scan) observations. These data provide evidence for significant spectral variations over the period. In the framework of the accreting black hole phenomenology, the source was most of the time in the Hard State and occasionally switched to the so-called "Intermediate State". Using the results of the analysis performed on these data, we present and compare the spectral properties of the source over the whole energy range (5 keV-1 MeV) covered by the high-energy instruments on board INTEGRAL, in both observed spectral states. Fe line and reflection component evolution occurs with spectral changes in the hard and soft components. The observed behaviour of Cygnus X-1 is consistent with the general picture of galactic black holes. Our results give clues to the physical changes that took place in the system (disc and corona) at almost constant luminosity during the spectral transitions and provide new measures of the spectral model parameters. In particular, during the Intermediate State of 2003 June, we observe in the Cygnus X-1 data a high-energy tail at several hundred keV in excess of the thermal Comptonization model which suggests the presence of an additional non-thermal component.
1 :  APC - UMR 7164 - AstroParticule et Cosmologie
2 :  SAp - Service d'Astrophysique
3 :  AIM - UMR 7158 - Astrophysique Interactions Multi-échelles
4 :  CAMK - Centrum Astronomiczne im. M. Kopernika
5 :  IASF-Bo - Istituto di Astrofisica Spaziale e Fisica cosmica - Bologna
6 :  CESR - Centre d'étude spatiale des rayonnements
Planète et Univers/Astrophysique/Phénomènes cosmiques de haute energie

Physique/Astrophysique/Phénomènes cosmiques de haute energie
black hole physics – stars: individual: Cygnus X-1 – gamma rays: observations – X-rays: binaries – X-rays: general
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