The high-energy emission from HD~93129A near periastron
Abstract
We conducted an observational campaign towards one of the most massive and luminous colliding wind binaries in the Galaxy, HD~93129A, close to its periastron passage in 2018. During this time the source was predicted to be in its maximum of high-energy emission. Here we present our data analysis from the X-ray satellites Chandra and NuSTAR and the γ-ray satellite AGILE. High-energy emission coincident with HD~93129A was detected in the X-ray band up to 18~keV, whereas in the γ-ray band only upper limits were obtained. We interpret the derived fluxes using a non-thermal radiative model for the wind-collision region. We establish a conservative upper limit for the fraction of the wind kinetic power that is converted into relativistic electron acceleration, fNT,e < 0.02. In addition, we set a lower limit for the magnetic field in the wind-collision region as BWCR > 0.3~G. We also argue a putative interpretation of the emission from which we estimate fNT,e ≈ 0.006 and BWCR ≈ 0.5~G. We conclude that multi-wavelength, dedicated observing campaigns during carefully selected epochs are a powerful tool for characterising the relativistic particle content and magnetic field intensity in colliding wind binaries.