Helen Meskhidze

Project abstract

Massive stars end their lives with powerful supernova explosions that, in extreme cases, may produce a gamma-ray burst. The driving mechanisms of these bursts are relativistic jets that propagate through the dense, rapidly rotating star. Previous studies have examined the general formation and photospheric emissions of the cocoons of these jets. However, the structure of the cocoon and the effect of cocoon composition on the creation of the gamma-ray burst have not yet been determined. In this study, we present the results of numerical simulations aimed at determining the composition and mixing of the cocoon material in gamma-ray burst progenitors and study how mixing affects the emitted radiation. We do so by adding tracer particles to special relativistic hydrodynamic simulations of collapsars to follow the mixing of matter within the cocoon as it evolves. Using this data, we compute the radiation signatures of cocoons from different progenitor stars with varying cocoon mixing. These simulations will enable us to understand the luminosity and radiation properties of the cocoon. When compared to observations, our calculations may put constraints on the progenitor stars structure that produces gamma-ray bursts.