Colliding wind binaries consist of two massive stars, each possessing a strong radiatively-driven stellar wind. The collision of these winds produces a strong, hot shock between the two stars which is a strong source of thermal X-rays. The shock can also accelerate particles by the Fermi process, producing a non-thermal population of leptons and hadrons, along with non-thermal radiation at hard X-ray to gamma-ray energies. The WR140 binary system is the best studied colliding wind binary. It has an extremely eccentric orbit so that densities and pressures in the shock change in a predictable way. Detailed monitoring of the thermal X-ray emission by NICER, measurement of the flow dynamics using X-ray line profiles from high-resolution XRISM spectra, combined with measures of the hard non-thermal X-ray emission using NuSTAR during WR140’s upcoming periastron passage this fall provides us a unique opportunity to measure the physical connection between the hot shocked gas, the non-thermal particle population and the high-energy photons in a well-behaved, predictable astrophysical shock.

Author: Mike Corcoran (Senior Research Scientist, The Catholic University of America & NASA/GSFC), Alina Kiesling (NuSTAR Project Manager).