Effect of Fluid Composition on a Jet Breaking out of a Cocoon in Gamma-Ray Bursts: A Relativistic de Laval Nozzle Treatment

In this paper we carry out a semi-analytic general relativistic study of Gamma-Ray Bursts (GRB) jet that is breaking cocoon or stellar envelope. We solve hydrodynamic equations with the equation state takes care fluid composition. short GRBs, approach required to account for curved spacetime in strong gravity. The piercing through resembles de Laval nozzle and may go recollimation shock transitions. show possibility transition properties are sensitive matter composition strength. Obtained Lorentz factors thermally driven jets comfortably reach few ×10.