Dynamic Monte Carlo Simulations of Radiatively Accelerated GRB Fireballs

Abstract

We present a novel Dynamic Monte Carlo code (DynaMo code) which self-consistently simulates the Compton scattering driven dynamic evolution of a plasma. We use the DynaMo code to investigate the time-dependent expansion and acceleration of dissipationless GRB fireballs by varying their initial opacities and baryonic content. We study the opacity and energy density evolution of an initially optically thick, radiation-dominated fireball across its entire phase space - in particular during the $R_{\mathrm{ph}}<R_{\mathrm{sat}}$ regime. Our results reveal new phases of fireball evolution: a transition phase with a radial extent of several orders of magnitude - the fireball transitions from $\Gamma \propto R$ to $\Gamma \propto R^0$, a post-photopsheric acceleration phase - where fireballs accelerate beyond the photosphere, and a Thomson-dominated acceleration phase - characterized by slow acceleration of optically thick, matter-dominated fireballs due to Thomson scattering. We quantify the new phases by providing analytical expressions of Lorentz factor evolution, which will be useful for deriving jet parameters.

16 pages, 12 figures, MNRAS accepted. Comments still Welcome!

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Cited by in corpus (3)

• Off-axis emission of short gamma-ray bursts and the detectability of electromagnetic counterparts of gravitational wave detected binary mergers
• The Fraction of Gamma-ray Bursts with an Observed Photospheric Emission Episode
• Non-dissipative photospheres in GRBs: Spectral appearance in the Fermi/GBM catalogue