MG13 - Talk detail

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A long gamma-ray burst (GRB) is thought to occur at the end of the evolution of certain massive stars. If so, it has to propagate through a complex environment, which has been shaped by the stellar wind of the progenitor star. Because the morphology of the circumstellar medium is a direct result of the properties of the stellar wind, and the properties of the stellar wind are directly linked to the evolution of the star, the circumstellar medium can provide us with insight as to the nature of the star. By comparing observational data with numerical models we may be able to learn which stars are GRB progenitors. We use existing stellar evolution models to generate time-dependent models of the winds of those massive stars that are thought to produce gamma-ray bursts, with these wind parameters as input, we use the MPI-AMRVAC hydrodynamics code to simulate the evolution of the circumstellar medium up to the end the star's life. From the final result we predict how the circumstellar medium would show up in the gamma-ray burst observation. We find that this can occur in two ways: 1) Circumstellar shells can show up as absorption features in the spectrum of a GRB afterglow. 2) The density profile of the circumstellar gas influences the shape of the lightcurve of the GRB afterglow. Our models also serve as input for simulation of the GRB jet itself.

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