Schedule Feb 10, 2006
Evolution of the Circumstellar Medium around a Gamma-Ray Burst Progenitor
A-J van Marle, N Langer, S-C Yoon, G Garcia-Segura

We present the results of hydrodynamical simulations of the circumstellar medium around a Gamma-ray burst progenitor. We use the mass loss history of a rapidly rotating, low metallicity massive star as input for our simulations. The interior of this star is homogeneous due to rotational mixing. In general, the mass loss rate of this star is low, while the wind velocity is high, except when the star reaches critical rotation. During these periods, the star produces adense, highly anisotropic wind, which radically changes the morphology of the circumstellar medium. From our simulations we can predict the density profile of the circumstellar medium along the polar axis of the star, which is the medium into which the gamma-ray burst jet would expand. We can also predict the likelihood of blue shifted absorption lines in the afterglow spectrum.

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