Radio study of the colliding wind binary HD93129A near periastron and its surroundings

Abstract

HD93129A is an O+O stellar system whose CWR has been mapped by high angular resolution observations at cm wavelengths. The synchrotron nature of the radio emission confirms its particle accelerator status. According to astrometric measurements since 1996, the system has an orbital period of ~120 yr and recently went through its periastron passage. We characterize the radio emission during the epoch of periastron passage, when the particle density and the local magnetic energy density in the CWR increase. We monitored HD93129A and surroundings at 2.1, 5.5 and 9 GHz with the ATCA over 17 months, with a ~2-month cadence. Previous ATCA data and data collected using other radio observatories were also included. We obtained radio light curves in subbands per band per epoch. The flux densities show an average rise of a factor four from 2003 to 2018, with the caveat that the 2009-2018 time lapse is devoid of data, and a similar decay between 2018 to 2020. We fit the spectral energy distribution of quasi-simultaneous data at three epochs and find that the magnetic-to-thermal pressure ratio does not remain constant along the orbit, possible suggesting magnetic field amplification close to periastron. In the 2019 epoch, we estimate a magnetic field strength of ~1.1G in the apex of the CWR. The evolution of the SED and spectral index is also presented. By combining ATCA and ASKAP images a spectral index map was obtained in an area of 30' size. The radio emission in the direction of other massive binary systems in the field (WR22, WR25 and HD93250) was measured and briefly discussed. Intensive radio monitoring allows us to track the evolution of physical conditions in the shocks. The general trend of decreasing emission of HD93129A in the high-frequency bands in 2019-2020 suggests that the system is at post-periastron, consistent with model predictions. (Abridged)

12 pages + 1 (appendix), 11 figures; to be accepted in A&A

References in corpus (26)

• Physical Properties of Wolf-Rayet Stars
• Southern Massive Stars at High Angular Resolution: Observational Campaign and Companion Detection
• Incremental Fermi Large Area Telescope Fourth Source Catalog
• The Galactic WC stars: Stellar parameters from spectral analyses indicate a new evolutionary sequence
• The Rapid ASKAP Continuum Survey Paper II: First Stokes I Source Catalogue Data Release
• Detection of Gamma-ray Emission from the Eta-Carinae Region
• Non-thermal emission processes in massive binaries
• Non-thermal X-rays from Colliding Wind Shock Acceleration in the Massive Binary Eta Carinae
• A close encounter of the massive kind
• Line Luminosities of Galactic and Magellanic Cloud Wolf-Rayet stars
• A radio-map of the colliding winds in the very massive binary system HD 93129A
• 3D magneto-hydrodynamic models of non-thermal photon emission in the binary system ${\gamma }^2$ Velorum
• AU-scale radio imaging of the wind collision region in the brightest and most luminous non-thermal colliding wind binary Apep
• Sub-mm free-free emission from the winds of massive stars in the age of ALMA
• A VLBI study of the wind-wind collision region in the massive multiple HD 167971
• Long-term soft and hard X-ray investigation of the colliding wind WN+O binary WR 25
• Probing the non-thermal physics of stellar bow shocks using radio observations
• Evidence for non-thermal X-ray emission from the double WR colliding-wind binary Apep
• Hints about the multiplicity of WR 133 based on multiepoch radio observations
• Investigation of the WR 11 field at decimeter wavelengths
• The high-energy emission from HD~93129A near periastron
• The Carina Nebula and Gum 31 molecular complex III: The distribution of the 1-3 GHz radio continuum across the whole nebula
• The non-thermal emission from the colliding-wind binary Apep
• $\gamma$-ray detection from occasional flares in T Tauri stars of NGC 2071. I. Observational connection
• The integrated radio spectrum of G2.4$+$1.4
• Detection of very-high-energy gamma-ray emission from Eta Carinae during its 2020 periastron passage