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

V. Beckmann, S. Soldi, G. Belanger, Søren Kristian Brandt, M.D. Caballero-Garcia, G. De Cesare, N. Gehrels, S. Grebenev, O. Vilhu, A. von Kienlin, T.J.L. Courvoisier

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

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 x 10(22) cm(-2)) black body model, whereas the X-ray spectrum above 20 keV appears to be extremely low and hard (Gamma similar or equal to 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 similar to 3, while the hard X- ray emission rises by a factor of similar to 14 and becomes steeper (up to Gamma = 4). Conclusions. The ultrasoft state apparently precedes the emission of a jet, which is apparent in the radio and hard X-ray domain.
Original languageEnglish
JournalAstronomy & Astrophysics
Volume473
Issue number3
Pages (from-to)903-905
ISSN0004-6361
DOIs
Publication statusPublished - 2007

Keywords

  • stars : Wolf-Rayet
  • stars : binaries : close
  • X-rays : individuals : Cyg X-3
  • stars : individual : Cyg X-3
  • X-rays : stars
  • X-rays : binaries

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