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Article Dans Une Revue Astronomy and Astrophysics - A&A Année : 2007

Cygnus X-3 transition from the ultrasoft to the hard state

Résumé

Aims:The nature of Cygnus X-3 is still not understood well. This binary system might host a black hole or a neutron star. Recent observations by INTEGRAL have shown that Cygnus X-3 was again in an extremely ultrasoft state. Here we present our analysis of the transition from the ultrasoft state, dominated by blackbody radiation at soft X-rays plus non-thermal emission in the hard X-rays, to the low hard state. Methods: INTEGRAL observed Cyg X-3 six times during three weeks in late May and early June 2007. Data from IBIS/ISGRI and JEM-X1 were analysed to show the spectral transition. Results: During the ultrasoft state, the soft X-ray spectrum is well-described by an absorbed (NH = 1.5 × 1022~cm-2) black body model, whereas the X-ray spectrum above 20 keV appears to be extremely low and hard (Γ ≃ 1.7). During the transition, the radio flux rises to a level of >1~Jy, and the soft X-ray emission drops by a factor of ~3, while the hard X-ray emission rises by a factor of ~14 and becomes steeper (up to Γ = 4). Conclusions: The ultrasoft state apparently precedes the emission of a jet, which is apparent in the radio and hard X-ray domain. Based on observations with INTEGRAL, an ESA project with instruments and science data centre funded by ESA member states (especially the PI countries: Denmark, France, Germany, Italy, Switzerland, Spain), Czech Republic and Poland, and with the participation of Russia and the USA.

Dates et versions

hal-00728371 , version 1 (05-09-2012)

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V. Beckmann, S. Soldi, G. Bélanger, S. Brandt, M. D. Caballero-García, et al.. Cygnus X-3 transition from the ultrasoft to the hard state. Astronomy and Astrophysics - A&A, 2007, 473, pp.903-905. ⟨10.1051/0004-6361:20078160⟩. ⟨hal-00728371⟩
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