000002028 001__ 2028
000002028 005__ 20160701171657.0
000002028 0247_ $$2DOI$$a10.1111/j.1365-2966.2006.10746.x
000002028 037__ $$aASTROimport-185
000002028 100__ $$aDe Becker, M.
000002028 245__ $$aXMM-Newton observations of the massive colliding wind binary and non-thermal radio emitter CygOB2#8A [O6If + O5.5III(f)]
000002028 260__ $$c2006
000002028 520__ $$aWe 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). 
000002028 700__ $$a Rauw, G.
000002028 700__ $$a Sana, H.
000002028 700__ $$a Pollock, A. M. T.
000002028 700__ $$a Pittard, J. M.
000002028 700__ $$a Blomme, R.
000002028 700__ $$a Stevens, I. R.
000002028 700__ $$a van Loo, S.
000002028 773__ $$c1280-1294$$i3$$pMonthly Notices of the Royal Astronomical Society$$v371$$y2006
000002028 85642 $$ahttp://esoads.eso.org/abs/2006MNRAS.371.1280D
000002028 905__ $$apublished in
000002028 980__ $$aREFERD