Reference : XMM-Newton observations of the massive colliding wind binary and non-thermal radio emitt...
Scientific journals : Article
Physical, chemical, mathematical & earth Sciences : Space science, astronomy & astrophysics
http://hdl.handle.net/2268/2772
XMM-Newton observations of the massive colliding wind binary and non-thermal radio emitter Cyg OB2#8A [O6If+O5.5III(f)]
English
De Becker, Michaël mailto [Université de Liège - ULg > Département d'astrophys., géophysique et océanographie (AGO) > Groupe d'astrophysique des hautes énergies (GAPHE) >]
Rauw, Grégor mailto [Université de Liège - ULg > Département d'astrophys., géophysique et océanographie (AGO) > Groupe d'astrophysique des hautes énergies (GAPHE) >]
Sana, H. [> > > >]
Pollock, A. M. T. [> > > >]
Pittard, J. M. [> > > >]
Blomme, Ronny [Royal Observatory of Belgium]
Stevens, I. R. [> > > >]
Van Loo, S. [> > > >]
21-Sep-2006
Monthly Notices of the Royal Astronomical Society
Blackwell Publishing
371
3
1280-1294
Yes (verified by ORBi)
International
0035-8711
Oxford
[en] stars : binaries : general ; stars : early-type ; stars : individual : Cyg OB2#8A ; stars : winds, outflows ; X-rays : stars
[en] We report on the results of four XMM-Newton observations separated by about ten days from each other of Cyg OB2 #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 10.0 keV is essentially thermal, and is best fitted with a three-component model with temperatures of about 3, 9 and 20 MK. The X-ray luminosity corrected for the interstellar absorption is rather large, i.e. about 1034 erg s(-1). Compared to the 'canonical' L-X/L-bol ratio of O-type stars, Cyg OB2 # 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 10.0 keV) 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 Cyg OB2 # 8A revealed by our investigation point undoubtedly to X-ray emission dominated by colliding winds.
http://hdl.handle.net/2268/2772
http://www3.interscience.wiley.com/cgi-bin/fulltext/118550367/HTMLSTART?CRETRY=1&SRETRY=0

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