XMM-Newton observations of the massive colliding wind binary and non-thermal radio emitter CygOB2#8A [O6If + O5.5III(f)]

Details XMM-Newton observations of the massive colliding wind binary and non-thermal radio emitter CygOB2#8A [O6If + O5.5III(f)] XMM-Newton observations of the massive colliding wind binary and non-thermal radio emitter CygOB2#8A [O6If + O5.5III(f)]

Sep 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006mnras.371.1280d&link_type=abstract

Monthly Notices of the Royal Astronomical Society, Volume 371, Issue 3, pp. 1280-1294.

Astronomy and Astrophysics

Astronomy

31

Stars: Binaries: General: Stars: Early-Type: Stars: Individual: Cygob2#8A: Stars: Winds, Outflows: X-Rays: Stars, Stars: Binaries: General, Stars: Early-Type, Stars: Individual: Cygob2#8A, Stars: Winds, Outflows, X-Rays: Stars

Scientific paper

We report on the results of four XMM-Newton observations separated by about ten days from each other of CygOB2#8A [O6If + O5.5III(f)]. This massive colliding wind binary is a very bright X-ray emitter - one of the first X-ray emitting O-stars discovered by the Einstein satellite - as well as a confirmed non-thermal radio emitter whose binarity was discovered quite recently. The X-ray spectrum between 0.5 and 10.0keV is essentially thermal, and is best fitted with a three-component model with temperatures of about 3, 9 and 20MK. The X-ray luminosity corrected for the interstellar absorption is rather large, i.e. about 1034ergs-1. Compared to the `canonical' LX/Lbol ratio of O-type stars, CygOB2#8A was a factor of 19-28 overluminous in X-rays during our observations. The EPIC spectra did not reveal any evidence for the presence of a non-thermal contribution in X-rays. This is not unexpected considering that the simultaneous detections of non-thermal radiation in the radio and soft X-ray (below 10.0keV) domains is unlikely. Our data reveal a significant decrease in the X-ray flux from apastron to periastron with an amplitude of about 20 per cent. Combining our XMM-Newton results with those from previous ROSAT-PSPC and ASCA-SIS observations, we obtain a light curve suggesting a phase-locked X-ray variability. The maximum emission level occurs around phase 0.75, and the minimum is probably seen shortly after the periastron passage. Using hydrodynamic simulations of the wind-wind collision, we find a high X-ray emission level close to phase 0.75, and a minimum at periastron as well. The high X-ray luminosity, the strong phase-locked variability and the spectral shape of the X-ray emission of CygOB2#8A revealed by our investigation point undoubtedly to X-ray emission dominated by colliding winds.
Based on observations with XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member states and the USA (NASA).
E-mail: debecker@astro.ulg.ac.be ‡
Research Associate FNRS (Belgium).

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