On the Multiplicity of the O-Star Cyg OB2 #8a and its Contribution to the γ-ray Source 3EG J2033+4118

Becker, M. De; Rauw, Grégor; Swings, Jean-Pierre

doi:10.1007/s10509-005-7667-x

Cited by 9 publications

(11 citation statements)

References 21 publications

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“…As Cyg OB2 #8A is a binary system, one could wonder whether the existing X‐ray observations reveal a modulation of the X‐ray flux. This issue was first addressed by De Becker et al (2005a) where the results from several X‐ray observations ( ROSAT and ASCA ) were combined to obtain a phase‐folded light curve, on the basis of the ephemeris published by De Becker et al (2004c). The light curve suggested a phase‐locked modulation of the X‐ray flux, probably due to the combined effect of the variation of the absorption along the line of sight and of the X‐ray emission itself as a function of orbital phase.…”

Section: Discussionmentioning

confidence: 99%

“…We mention that an alternative scenario was proposed by Jardine, Allen & Pollock (1996), but we will assume here that the first‐order Fermi mechanism in the presence of hydrodynamic shocks (the so‐called diffusive shock acceleration–DSA–mechanism) is the dominant process. For a discussion of the physical processes involved in the general scenario of the non‐thermal emission from massive stars, we refer, for example, to De Becker, Rauw & Swings (2005a) and references therein. The issue to be addressed here is that of the nature of these shocks: are they intrinsic to the stellar winds (see e.g.…”

Section: Introductionmentioning

confidence: 99%

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XMM��Newtonobservations of the massive colliding wind binary and non-thermal radio emitter Cyg��OB2��#8A [O6If + O5.5III(f)]

Becker

Rauw

Sana

et al. 2006

Monthly Notices of the Royal Astronomical Society

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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’LX/Lbol 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.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

XMM��Newtonobservations of the massive colliding wind binary and non-thermal radio emitter Cyg��OB2��#8A [O6If + O5.5III(f)]

Becker

Rauw

Sana

et al. 2006

Monthly Notices of the Royal Astronomical Society

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“…However, De Becker et al caution that the observed variability might be attributed to systematic effects between XMM-Newton and ROSAT data, as seen in Cyg OB2 No. 8A (De Becker et al 2005a). …”

Section: Colliding-wind Region Between the Supergiant And The Binarymentioning

confidence: 97%

Non-thermal radio emission from O-type stars

Blomme¹,

Becker

Runacres

et al. 2007

A&A

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HD 167971 is a triple system consisting of a 3.3-day eclipsing binary (O5−8 V + O5−8 V) and an O8 supergiant. It is also a well known non-thermal radio emitter. We observed the radio emission of HD 167971 with the Very Large Array (VLA) and the Australia Telescope Compact Array (ATCA). By combining these data with VLA archive observations we constructed a radio lightcurve covering a 20-yr time-range. We searched for, but failed to find, the 3.3-day spectroscopic period of the binary in the radio data. This could be due to the absence of intrinsic synchrotron radiation in the colliding-wind region between the two components of the eclipsing binary, or due to the large amount of free-free absorption that blocks the synchrotron radiation. We are able to explain many of the observed characteristics of the radio data if the non-thermal emission is produced in a colliding-wind region between the supergiant and the combined winds of the binary. Furthermore, if the system is gravitationally bound, the orbital motion occurs over a period of ∼20 years or longer, as suggested by the long-term variability in the radio data. We argue that the variability is due to the free-free absorption that changes with orbital phase or may also in part be due to changes in separation, should the orbit be eccentric.

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“…De Becker 2005). The putative contribution of some of these early-type stars to the γ-ray source 3EG J2033+4118 has already been discussed by Benaglia et al (2001) and De Becker et al (2005b). In addition, a few long-period Wolf-Rayet binaries (WR 140,WR 146,and WR 147) located close to Cyg OB2 are also classified as non-thermal radio emitters, and may therefore be non-thermal high-energy sources.…”

Section: Introductionmentioning

confidence: 86%

INTEGRAL-ISGRI observations of the Cygnus OB2 region

Becker¹,

Rauw²,

Pittard³

et al. 2007

A&A

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Aims. We analyze INTEGRAL-ISGRI data in order to probe the hard X-ray emission (above 20 keV) from point sources in the Cyg OB2 region and to investigate the putative non-thermal high-energy emission from early-type stars (Wolf-Rayet and O-type stars). Among the targets located in the field of view, we focus on the still unidentified EGRET source 3EG 2033+4118 that may be related to massive stars known to produce non-thermal emission in the radio domain, and on the wide colliding-wind binary WR 140. Methods. Using a large set of data obtained with the IBIS-ISGRI imager onboard INTEGRAL, we run the OSA software package in order to find point sources in the fully coded field of view of the instrument. Results. Our data do not allow the detection of a lower-energy counterpart of 3EG J2033+4118 nor of any other new point sources in the field of view, and we derive upper limits on the high-energy flux for a few targets: 3EG J2033+4118, TeV J2032+4130, WR 140, WR 146 and WR 147. The results are discussed in the context of the multiwavelength investigation of these objects. Conclusions. The upper limits derived are valuable constraints for models aimed at understanding the acceleration of particles in non-thermal emitting massive stars, and of the still unidentified very-high gamma-ray source TeV J2032+4130.

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On the Multiplicity of the O-Star Cyg OB2 #8a and its Contribution to the γ-ray Source 3EG J2033+4118

Cited by 9 publications

References 21 publications

XMM��Newtonobservations of the massive colliding wind binary and non-thermal radio emitter Cyg��OB2��#8A [O6If + O5.5III(f)]

XMM��Newtonobservations of the massive colliding wind binary and non-thermal radio emitter Cyg��OB2��#8A [O6If + O5.5III(f)]

Non-thermal radio emission from O-type stars

INTEGRAL-ISGRI observations of the Cygnus OB2 region

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On the Multiplicity of the O-Star Cyg OB2 #8a and its Contribution to the γ-ray Source 3EG J2033+4118

Cited by 9 publications

References 21 publications

XMM���Newtonobservations of the massive colliding wind binary and non-thermal radio emitter Cyg���OB2���#8A [O6If + O5.5III(f)]

XMM���Newtonobservations of the massive colliding wind binary and non-thermal radio emitter Cyg���OB2���#8A [O6If + O5.5III(f)]

Non-thermal radio emission from O-type stars

INTEGRAL-ISGRI observations of the Cygnus OB2 region

Contact Info

Product

Resources

About

XMM��Newtonobservations of the massive colliding wind binary and non-thermal radio emitter Cyg��OB2��#8A [O6If + O5.5III(f)]

XMM��Newtonobservations of the massive colliding wind binary and non-thermal radio emitter Cyg��OB2��#8A [O6If + O5.5III(f)]