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

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 ~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. 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 TIFR 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 free-free absorption. Finally, we report on the identification of two additional particle-accelerating colliding-wind binaries, namely Cyg OB2 12 and ALS 15108 AB.

20 pages, 20 figures, 6 tables, accepted in PASA

References in corpus (9)

• Physical Properties of Wolf-Rayet Stars
• The High Angular Resolution Multiplicity of Massive Stars
• Toward Complete Statistics of Massive Binary Stars: Penultimate Results from the Cygnus OB2 Radial Velocity Survey
• Detection of Gamma-ray Emission from the Eta-Carinae Region
• Unlocking Galactic Wolf-Rayet stars with $\text{Gaia}$ DR2 I: Distances and absolute magnitudes
• Gemini/GNIRS infrared spectroscopy of the Wolf-Rayet stellar wind in Cygnus X-3
• Simulating three-dimensional nonthermal high-energy photon emission in colliding-wind binaries
• The population of radio sources in the field of the unidentified gamma-ray source TeV J2032+4130
• 3D magneto-hydrodynamic models of non-thermal photon emission in the binary system ${\gamma }^2$ Velorum

Cited by in corpus (7)

• Particle acceleration and non-thermal emission in colliding-wind binary systems
• High-sensitivity radio study of the non-thermal stellar bow shock EB27
• Radio modelling of the brightest and most luminous non-thermal colliding-wind binary Apep
• Quest for the upcoming periastron passage of an episodic dust maker and particle accelerating colliding wind binary: WR 125
• Radio counterparts of gamma-ray sources in the Cygnus region
• Strong low-frequency radio flaring from Cygnus X-3 observed with LOFAR
• Investigation of the double-lobed sources of the Cygnus constellation core