Impact of Relativistic Fireballs on External Matter Numerical Models of Cosmological Gamma.pdf

IMPACT OF RELATIVISTIC FIREBALLS ON EXTERNAL MATTER: NUMERICAL MODELS OF COSMOLOGICAL GAMMA-RAY BURSTS A. Panaitescu, L. Wen1, P. Laguna2 P. M´esz´aros2 Department of Astronomy Astrophysics, Pennsylvania State University, University Park, PA 16802 7 9 ABSTRACT 9 1 r We numerically model the interaction between an expanding fireball and a stationary a external medium whose density is either homogeneous or varies with distance as a power-law. M The evolution is followed until most of the fireball kinetic energy is converted into internal 8 energy. The density, pressure and flow Lorentz factor profiles are shown at different stages, 2 including shock and rarefaction wave reflections, for a fireball of initial bulk Lorentz factor Γ = 100, both in the adiabatic and non-adiabatic (radiative) regimes. For cooling times shorter 2 v than the dynamic time, bolometric light-curves are computed for values of Γ = 50, 100 and 200. 4 We compare the numerical light-curves with analytic results, and find that for a homogeneous 6 external medium there is a simple scaling relationship among light-curves obtained for different 0 0 parameters. The light-curves for power-law external densities are similar in shape to those in 1 the homogeneous case. We discuss the implications of a comparison of the results with observed 6 Gamma-Ray Burst time histories. 9 / h p Subject headings: gamma-rays: bursts - hydrodynamics - methods: numerical - relativity - shock - o wave