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Recent reports claiming tentative association of the massive star binary system gamma^2 Velorum (WR 11) with a high-energy gamma-ray source observed by Fermi-LAT contrast the so-far exclusive role of Eta Carinae as the hitherto only detected gamma-ray emitter in the source class of particle-accelerating colliding-wind binary systems. We aim to shed light on this claim of association by providing dedicated model predictions for the nonthermal photon emission spectrum of WR 11. We use three-dimensional magneto-hydrodynamic modeling to trace the structure and conditions of the wind-collision region of WR 11 throughout its 78.5 day orbit, including the important effect of radiative braking in the stellar winds. A transport equation is then solved in the wind-collision region to determine the population of relativistic electrons and protons which are subsequently used to compute nonthermal photon emission components. We find that - if WR 11 be indeed confirmed as the responsible object for the observed gamma-ray emission - its radiation will unavoidably be of hadronic origin owing to the strong radiation fields in the binary system which inhibit the acceleration of electrons to energies suffciently high for observable inverse Compton radiation. Different conditions in wind-collision region near the apastron and periastron configuration lead to significant variability on orbital time scales. The bulk of the hadronic gamma-ray emission originates at a 400 solar radii wide region at the apex.
Many early-type stars are in systems; some of them have been indicated as putative high-energy emitters. The radiation is expected to be produced at the region where two stellar winds collide. Compelling evidence of such emission was found only for t
We examine the dependence of the wind-wind collision and subsequent X-ray emission from the massive WR+O star binary WR~22 on the acceleration of the stellar winds, radiative cooling, and orbital motion. Simulations were performed with instantaneousl
We study thermal emission from circumstellar structures heated by gamma-ray burst (GRB) radiation and ejecta and calculate its contribution to GRB optical and X-ray afterglows using the modified radiation hydro-code small STELLA. It is shown that the
GRB spectra appear non-thermal, but recent observations of a few bursts with Fermi GBM have confirmed previous indications from BATSE of the presence of an underlying thermal component. Photospheric emission is indeed expected when the relativistic o
More than a dozen binary systems are now established as sources of variable, high energy (HE, 0.1-100 GeV) gamma rays. Five are also established sources of very high energy (VHE, >100 GeV) gamma rays. The mechanisms behind gamma-ray emission in binar