WSRT 1.4 and 5-GHz light curves for WR 147 (AS 431, WN8(h)+OB)

Gunawan, D. Y. A. Setia; Bruyn, de Antonius; Hucht, K. van der; Williams, P. M.

doi:10.1051/0004-6361:20000561

Cited by 36 publications

(69 citation statements)

References 29 publications

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“…Moreover, it is still under debate whether the secondary in WR 146 is an O8V star or another binary (Setia Gunawan et al 2000). Despite this uncertainty in the composition of the secondary, the very high resolution image from O'Connor et al (2005) shows signs of only one WCR, so it seems unlikely that our results are biased by the behavior of the secondary.…”

Section: Source Variability and Possible Contaminationmentioning

confidence: 80%

Synchrotron radiation and absence of linear polarization in the colliding wind binary WR 146

Hales

Benaglia

Palacio

et al. 2017

A&A

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Context. Several massive early-type binaries exhibit non-thermal emission which has been attributed to synchrotron radiation from particles accelerated by diffusive shock acceleration (DSA) in the wind-collision region (WCR). If the magnetic field in the strong shocks is ordered, its component parallel to the shock front should be enhanced, and the resultant synchrotron radiation would be polarized. However, such polarization has never been measured. Aims. We aim to determine the percentage of linearly polarized emission from the well-known non-thermal radio emitter WR 146, a WC6+O8 system. Methods. We performed spatially-unresolved radio continuum observations of WR 146 at 5 cm and 20 cm with the Karl G. Jansky Very Large Array. We constructed a numerical model to investigate a scenario where particles are accelerated by turbulent magnetic reconnection (MR), and we performed a quantitative analysis of possible depolarization effects. Results. No linearly polarized radio emission was detected. The data constrain the fractional linear polarization to less than 0.6% between 1 to 8 GHz. This is compatible with a high level of turbulence and a dominant random component in the magnetic field. In this case the relativistic particles could be produced by turbulent magnetic reconnection. In order for this scenario to satisfy the required non-thermal energy budget, the strength of the magnetic field in the WCR must be as high as ∼ 150 mG. However, if the magnetic field is ordered and DSA is ongoing, then a combination of internal and external Faraday rotation could equally account for the depolarization of the emission. Conclusions. The absence of polarization could be caused by a highly turbulent magnetic field, other depolarization mechanisms such as Faraday rotation in the stellar wind, or a combination of these processes. It is not clear whether it is possible to develop the high level of turbulence and strong magnetic fields required for efficient MR in a long-period binary such as WR 146. This scenario might also have trouble explaining the low-frequency cutoff in the spectrum. We therefore favor a scenario where particles are accelerated through DSA and the depolarization is produced by mechanisms other than a large ratio between random to regular magnetic fields.

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Section: Source Variability and Possible Contaminationmentioning

confidence: 80%

Synchrotron radiation and absence of linear polarization in the colliding wind binary WR 146

Hales

Benaglia

Palacio

et al. 2017

A&A

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“…The shorter-term variability could be attributed to stochastic variations due to clumping in the stellar winds, as suggested for WR 146 and WR 147 (Setia Gunawan et al 2000, 2001. These affect the synchrotron emitting region itself (as the density and/or velocity of the material entering the colliding-wind region changes) and affect the free-free absorption.…”

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

confidence: 94%

Non-thermal radio emission from O-type stars

Blomme¹,

Becker

Runacres

et al. 2007

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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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“…These differences may be attributed to Churchwell et al 1992 andRodríguez 1999). The flux at both 22 and 43 GHz is highly uncertain, with the latter estimated from a long extrapolation of a power-law fit to the lower frequency "thermal" data points to be ≈2 mJy (Skinner et al 1999;Setia Gunawan et al 2001). Both high frequency points suggest a high frequency turn down.…”

Section: Modelling the Radio Spectrum Of Wr 147mentioning

confidence: 99%

Radio emission models of colliding-wind binary systems

Dougherty

Pittard

Kasian

et al. 2003

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Abstract. We present calculations of the spatial and spectral distribution of the radio emission from a wide WR+OB collidingwind binary system based on high-resolution hydrodynamical simulations and solutions to the radiative transfer equation. We account for both thermal and synchrotron radio emission, free-free absorption in both the unshocked stellar wind envelopes and the shocked gas, synchrotron self-absorption, and the Razin effect. To calculate the synchrotron emission several simplifying assumptions are adopted: the relativistic particle energy density is a simple fraction of the thermal particle energy density, in equipartition with the magnetic energy density, and a power-law in energy. We also assume that the magnetic field is tangled such that the resulting emission is isotropic. The applicability of these calculations to modelling radio images and spectra of colliding-wind systems is demonstrated with models of the radio emission from the wide WR+OB binary WR 147. Its synchrotron spectrum follows a power-law between 5 and 15 GHz but turns down to below this at lower and higher frequencies. We find that while free-free opacity from the circum-binary stellar winds can potentially account for the low-frequency turnover, models that also include a combination of synchrotron self-absorption and Razin effect are favoured. We argue that the highfrequency turn down is a consequence of inverse-Compton cooling. We present our resulting spectra and intensity distributions, along with simulated MERLIN observations of these intensity distributions. From these we argue that the inclination of the WR 147 system to the plane of the sky is low. We summarise by considering extensions of the current model that are important for models of the emission from closer colliding wind binaries, in particular the dramatically varying radio emission of WR 140.

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WSRT 1.4 and 5-GHz light curves for WR 147 (AS 431, WN8(h)+OB)

Cited by 36 publications

References 29 publications

Synchrotron radiation and absence of linear polarization in the colliding wind binary WR 146

Synchrotron radiation and absence of linear polarization in the colliding wind binary WR 146

Non-thermal radio emission from O-type stars

Radio emission models of colliding-wind binary systems

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