Speaker
Description
The majority of massive stars form a binary system with another massive star. Their strong winds with velocities at 1000-3000 km s$^{-1}$ collide between the two stars and produce stationary shocks. Several so-called colliding wind binary systems (CWBs) within a few kpc from the Sun produce shock-heated plasmas at ~3-5$\times 10^7$ K and emit luminous X-rays up to ~10$^{34-35}$ ergs s$^{-1}$. The shock should also accelerate a small number of particles to relativistic energies via the Fermi mechanism. In the 2010s, the NuSTAR and Fermi observatories with excellent sensitivities in the extremely hard X-rays (>10 keV) or GeV gamma-rays detected signatures of the accelerated, non-thermal particles from eta Carinae, a supermassive star with the strongest colliding wind activity in our Galaxy. The spectra suggest at least two components, perhaps originating from pion-decay radiation or inverse-Compton radiation of stellar UV radiation upscattered by the accelerated particles. I introduce the current understanding of particle acceleration in massive CWBs.
