Search for non-thermal X-ray emission in the colliding wind binary Cyg OB2 #8A
arXiv:2003.10262 · doi:10.1051/0004-6361/201936735
Abstract
Cyg OB2 #8a is a massive O-type binary displaying strong non-thermal radio emission. Owing to the compactness of this binary, emission of non-thermal X-ray photons via inverse Compton scattering is expected. We first revised the orbital solution for Cyg OB2 #8a using new optical spectra. We then reduced and analysed X-ray spectra obtained with XMM-Newton, Swift, INTEGRAL, and NuSTAR. The analysis of the XMM-Newton and Swift data allows us to better characterise the X-ray emission from the stellar winds and colliding winds region at energies below 10 keV. We confirm the variation of the broad-band light curve of Cyg OB2 #8a along the orbit with, for the first time, the observation of the maximum emission around phase 0.8. The minimum ratio of the X-ray to bolometric flux of Cyg OB2 #8a remains well above the level expected for single O-type stars, indicating that the colliding wind region is not disrupted during the periastron passage. The analysis of the full set of publicly available INTEGRAL observations allows us to refine the upper limit on the non-thermal X-ray flux of the Cyg OB2 region between 20 and 200 keV. Two NuSTAR observations (phases 0.028 and 0.085) allow us to study the Cyg OB2 #8a spectrum up to 30 keV. These data do not provide evidence of the presence of non-thermal X-rays, but bring more stringent constraints on the flux of a putative non-thermal component. Finally, we computed, thanks to a new dedicated model, the anisotropic inverse Compton emission generated in the wind shock region. The theoretical non-thermal emission appears to be compatible with observational limits and the kinetic luminosity computed from these models is in good agreement with the unabsorbed flux observed below 10 keV.
arXiv comment12 pages, 8 figures, A&A accepted
References in corpus (35)
- Gaia Data Release 2. Summary of the contents and survey properties
- On the Absorption of X-rays in the Interstellar Medium
- The European Photon Imaging Camera on XMM-Newton: The MOS Cameras
- The Nuclear Spectroscopic Telescope Array (NuSTAR) Mission
- Collisional Plasma Models with APEC/APED: Emission Line Diagnostics of Hydrogen-like and Helium-like Ions
- Atomic Data for Astrophysics. II. New Analytic Fits for Photoionization Cross Sections of Atoms and Ions
- Estimating distances from parallaxes IV: Distances to 1.33 billion stars in Gaia Data Release 2
- A new calibration of stellar parameters of Galactic O stars
- The INTEGRAL Science Data Centre (ISDC)
- On the role of injection in kinetic approaches to nonlinear particle acceleration at non-relativistic shock waves
- Chandra-HETGS Observations of the Brightest Flare Seen from Sgr A*
- Radio, X-ray, and gamma-ray Emission Models of the Colliding Winds Binary WR 140
- Non-thermal high-energy emission from colliding winds of massive stars
- Detection of Gamma-ray Emission from the Eta-Carinae Region
- 3D models of radiatively driven colliding winds in massive O+O star binaries - III. Thermal X-ray emission
- Fermi Large Area Telescope Observation of a Gamma-ray Source at the Position of Eta Carinae
- Radio emission models of Colliding-Wind Binary Systems - Inclusion of IC cooling
- X-ray emission from interacting massive binaries: a review of 15 years of progress
- A Spectroscopic study of the non-thermal radio emitter Cyg OB2 #8A: Discovery of a new binary system
- Hard X-ray emission from Eta Carinae
- Non-thermal X-rays from Colliding Wind Shock Acceleration in the Massive Binary Eta Carinae
- 3D models of radiatively driven colliding winds in massive O+O star binaries - II. Thermal radio to sub-mm emission
- Non-thermal radio emission from O-type stars. IV. Cyg OB2 No. 8A
- Colliding Stellar Winds Structure and X-ray Emission
- Hard X-ray identification of Eta Carinae and steadiness close to periastron
- Wind collisions in three massive stars of Cyg OB2
- Suzaku monitoring of the Wolf-Rayet binary WR140 around periastron passage: An approach for quantifying the wind parameters
- The 2.35 year itch of Cyg OB2 #9. II. Radio monitoring
- A model for the non-thermal emission of the very massive colliding-wind binary HD 93129A
- A modern study of HD166734: a massive supergiant system
- Super-hard X-Ray Emission from eta Carinae Observed with Suzaku
- An X-ray view of HD166734, a massive supergiant system
- The environment of the wind-wind collision region of Carinae
- Variable millimetre radiation from the colliding-wind binary Cyg OB2 #8A
- Interacting winds in massive binaries