Non-thermal radio emission from colliding-wind binaries: modelling Cyg OB2 No. 8A and No. 9

AbstractSome OB stars show variable non-thermal radio emission. The non-thermal emission is due to synchrotron radiation that is emitted by electrons accelerated to high energies. The electron acceleration occurs at strong shocks created by the collision of radiatively-driven stellar winds in binary systems. Here we present results of our modelling of two colliding wind systems: Cyg OB2 No. 8A and Cyg OB2 No. 9.

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Hints about the multiplicity of WR 133 based on multiepoch radio observations

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834493 ◽

2019 ◽

Vol 623 ◽

pp. A163 ◽

Cited By ~ 2

Author(s):

M. De Becker ◽

N. L. Isequilla ◽

P. Benaglia

Keyword(s):

Radio Emission ◽

Binary Systems ◽

Thermal Emission ◽

Radio Spectrum ◽

Particle Accelerator ◽

Stellar Winds ◽

Apparent Contradiction ◽

Thermal Radio Emission ◽

Massive Binary Systems ◽

Thermal Emission Spectrum

Several tens of massive binary systems display indirect, or even strong evidence for non-thermal radio emission, hence their particle accelerator status. These objects are referred to as particle-accelerating colliding-wind binaries (PACWBs). WR 133 is one of the shortest period Wolf-Rayet + O systems in this category, and is therefore critical to characterize the boundaries of the parameter space adequate for particle acceleration in massive binaries. Our methodology consists in analyzing JVLA observations of WR 133 at different epochs to search for compelling evidence for a phase-locked variation attributable to synchrotron emission produced in the colliding-wind region. New data obtained during two orbits reveal a steady and thermal emission spectrum, in apparent contradiction with the previous detection of non-thermal emission. The thermal nature of the radio spectrum along the 112.4-d orbit is supported by the strong free–free absorption by the dense stellar winds, and shows that the simple binary scenario cannot explain the non-thermal emission reported previously. Alternatively, a triple system scenario with a wide, outer orbit would fit with the observational facts reported previously and in this paper, albeit no hint for the existence of a third component exists to date. The epoch-dependent nature of the identification of synchrotron radio emission in WR 133 emphasizes the issue of observational biases in the identification of PACWBs, that undoubtedly affect the present census of PACWB among colliding-wind binaries.

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Non-thermal radio emission in Wolf-Rayet stars: is binarity a pre-requisite?

Symposium - International Astronomical Union ◽

10.1017/s0074180900205676 ◽

1999 ◽

Vol 193 ◽

pp. 348-349

Author(s):

Sean M. Dougherty

Keyword(s):

Radio Emission ◽

Spectral Index ◽

Thermal Emission ◽

Radio Observations ◽

Thermal Radio ◽

Thermal Radio Emission ◽

Thermal Emitters

Radio observations of Wolf-Rayet stars currently available in the literature are examined to determine whether binarity is a common feature of WR systems with non-thermal emission. Among 24 stars with observed spectral index values, seven are definite non-thermal emitters, and six others possibly have composite thermal/non-thermal spectra. Stellar companions have been identified in 71% of the non-thermal emitters, strongly supporting a link between non-thermal emission and binarity.

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Murchison Widefield Array detection of steep-spectrum, diffuse, non-thermal radio emission within Abell 1127

Publications of the Astronomical Society of Australia ◽

10.1017/pasa.2020.29 ◽

2020 ◽

Vol 37 ◽

Author(s):

S. W. Duchesne ◽

M. Johnston-Hollitt ◽

Z. Zhu ◽

R. B. Wayth ◽

J. L. B. Line

Keyword(s):

Radio Emission ◽

Galaxy Clusters ◽

Phase Ii ◽

Thermal Emission ◽

Low Frequency ◽

Radio Spectrum ◽

Discrete Source ◽

Thermal Radio ◽

Thermal Radio Emission ◽

Murchison Widefield Array

Abstract Diffuse, non-thermal emission in galaxy clusters is increasingly being detected in low-frequency radio surveys and images. We present a new diffuse, steep-spectrum, non-thermal radio source within the cluster Abell 1127 found in survey data from the Murchison Widefield Array (MWA). We perform follow-up observations with the ‘extended’ configuration MWA Phase II with improved resolution to better resolve the source and measure its low-frequency spectral properties. We use archival Very Large Array S-band data to remove the discrete source contribution from the MWA data, and from a power law model fit we find a spectral index of –1.83±0.29 broadly consistent with relic-type sources. The source is revealed by the Giant Metrewave Radio Telescope at 150 MHz to have an elongated morphology, with a projected linear size of 850 kpc as measured in the MWA data. Using Chandra observations, we derive morphological estimators and confirm quantitatively that the cluster is in a disturbed dynamical state, consistent with the majority of phoenices and relics being hosted by merging clusters. We discuss the implications of relying on morphology and low-resolution imaging alone for the classification of such sources and highlight the usefulness of the MHz to GHz radio spectrum in classifying these types of emission. Finally, we discuss the benefits and limitations of using the MWA Phase II in conjunction with other instruments for detailed studies of diffuse, steep-spectrum, non-thermal radio emission within galaxy clusters.

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