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

2019 ◽  
Vol 623 ◽  
pp. A163 ◽  
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.

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

2010 ◽  
Vol 6 (S272) ◽  
pp. 638-639 ◽  
Author(s):  
Delia Volpi ◽  
Ronny Blomme ◽  
Michael De Becker ◽  
Gregor Rauw
Keyword(s):  
Synchrotron Radiation ◽  
Radio Emission ◽  
Binary Systems ◽  
Thermal Emission ◽  
Electron Acceleration ◽  
Stellar Winds ◽  
Ob Stars ◽  
High Energies ◽  
Thermal Radio ◽  
Thermal Radio Emission

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.

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

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.

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

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.

scholarly journals Radio emission models of colliding-wind binary systems

2003 ◽  
Vol 212 ◽  
pp. 170-171
Author(s):  
Sean M. Dougherty ◽  
Julian M. Pittard ◽  
Laura Kasian ◽  
Robert F. Coker ◽  
Peredur M. Williams ◽  
...  
Keyword(s):  
High Resolution ◽  
Radio Emission ◽  
Binary Systems ◽  
Radiative Transfer Equation ◽  
Relativistic Particle ◽  
Particle Energy ◽  
Simple Fraction ◽  
Thermal Radio Emission ◽  
Emission Models ◽  
Hydrodynamical Simulations

We present preliminary calculations of the spatial distribution of the radio emission from a WR+OB colliding wind system, based on high-resolution hydrodynamical simulations and solutions to the radiative transfer equation. We account for both thermal and non-thermal radio emission, under the assumption of equipartition between magnetic and relativistic particle energy densities, and that the latter is a simple fraction of the thermal particle energy density. These calculations provide the foundation for modeling high resolution radio images and light curves of colliding-wind systems like WR 140, WR 146 and WR 147.

scholarly journals Physics of instabilities in radiatively driven stellar winds

1989 ◽  
Vol 113 ◽  
pp. 291-292
Author(s):  
S.P. Owocki ◽  
J.I. Castor ◽  
G.B. Rybicki
Keyword(s):  
Radio Emission ◽  
High Speed ◽  
Nonlinear Evolution ◽  
Spectral Lines ◽  
Stellar Winds ◽  
Clear Understanding ◽  
X Ray ◽  
Thermal Radio Emission ◽  
Shock Models ◽  
Dynamical Simulations

One type of variability that is ubiquitous among luminous blue stars is that associated with their massive stellar winds. Ultraviolet spectral lines show variable narrow absorption components that may arise from dense shells or clumps in the wind; the observed soft X-ray and non-thermal radio emission from these stars may be produced in embedded wind shocks associated with these shells. The line-driving of such winds is known to be strongly unstable, and recent numerical simulations of the dynamical, nonlinear evolution of such instabilities indicate that such shocks and dense shells do indeed form (Owocki, Castor, and Rybicki 1988; hereafter OCR). However, the structure computed in these dynamical simulations is quite different, and in some sense opposite, what was anticipated in earlier heuristic shock models (e.g. Lucy 1984, Krolik and Raymond 1985, Abbott 1988); the highest speed material is veryrarefied, not dense, and the strongest shocks that form are of thereverse, not forward, type. In subsequent simulations we have found that the detailed character of this structure can depend on many variables, but this tendency always to form high speed rarefied waves and reverse shocks is quite robust. It is thus important that we have a clear understanding of the reasons for this tendency, and it is on this point that we focus our comments here.

scholarly journals Megahertz emission of massive early-type stars in the Cygnus region

2020 ◽  
Vol 37 ◽  
Author(s):  
P. Benaglia ◽  
M. De Becker ◽  
C. H. Ishwara-Chandra ◽  
H. T. Intema ◽  
N. L. Isequilla
Keyword(s):  
Binary Systems ◽  
Thermal Emission ◽  
Spectral Energy Distribution ◽  
Wide Band ◽  
Type Systems ◽  
Radio Spectrum ◽  
Spectral Energy ◽  
Strong Impact ◽  
Early Type ◽  
Early Type Stars

Abstract Massive, early-type stars have been detected as radio sources for many decades. Their thermal winds radiate free–free continuum and in binary systems hosting a colliding-wind region, non-thermal emission has also been detected. To date, the most abundant data have been collected from frequencies higher than 1 GHz. We present here the results obtained from observations at 325 and 610 MHz, carried out with the Giant Metrewave Radio Telescope, of all known Wolf-Rayet and O-type stars encompassed in area of $\sim$ 15 sq degrees centred on the Cygnus region. We report on the detection of 11 massive stars, including both Wolf-Rayet and O-type systems. The measured flux densities at decimeter wavelengths allowed us to study the radio spectrum of the binary systems and to propose a consistent interpretation in terms of physical processes affecting the wide-band radio emission from these objects. WR 140 was detected at 610 MHz, but not at 325 MHz, very likely because of the strong impact of free–free absorption (FFA). We also report—for the first time—on the detection of a colliding-wind binary system down to 150 MHz, pertaining to the system of WR 146, making use of complementary information extracted from the Tata Institute of Fundamental Research GMRT Sky Survey. Its spectral energy distribution clearly shows the turnover at a frequency of about 600 MHz, that we interpret to be due to FFA. Finally, we report on the identification of two additional particle-accelerating colliding-wind binaries, namely Cyg OB2 12 and ALS 15108 AB.

scholarly journals SECONDARY EMISSION BEHIND THE RADIO OUTFLOWS IN GAMMA-RAY BINARIES

2010 ◽  
Vol 19 (06) ◽  
pp. 741-747 ◽  
Author(s):  
VALENTÍ BOSCH-RAMON
Keyword(s):  
Radio Emission ◽  
Binary Systems ◽  
Gamma Ray ◽  
Orbital Motion ◽  
Compact Object ◽  
Radio Spectrum ◽  
Secondary Emission ◽  
Primary Star ◽  
Structure Extension ◽  
The Impact

Several binary systems consisting of a massive star and a compact object have been detected above 100 GeV in the Galaxy. In most of these sources, gamma-rays show a modulation associated to the orbital motion, which means that the emitter should not be too far from the bright primary star. This implies that gamma-ray absorption will be non-negligible, and large amounts of secondary electron–positron pairs will be created in the stellar surroundings. In this work, we show that the radio emission from these pairs should be accounted for when interpreting the radio spectrum, variability, and morphology found in gamma-ray binaries. Relevant features of the secondary radio emission are the relatively hard spectrum, the orbital motion of the radio peak center and the radio structure extension following a spiral-like trajectory. The impact of the stellar wind free–free absorption should not be neglected.

Sign in / Sign up

Export Citation Format

Share Document