Dynamical Evolution of GammaRay Burst Remnants with Evolving Radiative Efficiency.pdfVIP

Chinese Journal of Astronomy and Astrophysics manuscript no. (Version: HuangYF.tex; printed on February 2, 2008; 1:16) Dynamical Evolution of Gamma-Ray Burst 2 Remnants with Evolving Radiative Efficiency 0 0 1 1,2 1 1,2 2 J. B. Feng , Y. F. Huang , Z. G. Dai and T. Lu t c O 1 Department of Astronomy, Nanjing University, Nanjing 210093, China 0 2 3 LCRHEA, Institute for High-Energy Physics, Chinese Academy of Sciences, Beijing 100039, China 1 v 6 5 Received 2002 ; accepted 2002 6 0 1 2 Abstract In previous works, a generic dynamical model has been suggested 0 / by Huang et al., which is shown to be correct for both adiabatic and radiative h p blastwaves, and in both ultra-relativistic and non-relativistic phases. In deriving - o their equations, Huang et al. have assumed that the radiative efficiency of the r t fireball is constant. They then applied their model directly to realistic cases where s a : the radiative efficiency evolves with time. In this paper, we abandon the above v i assumption and re-derive a more accurate dynamical equation for gamma-ray X burst remnants. Numerical results show that Huang et al.’s model is accurate r a enough in general cases. Key words: gamma rays: bursts — hydrodynamics — radiation mechanisms: nonthermal 1 INTRODUCTION Although the progenitors of gamma-ray bursts (GRBs) are still controversial (Cheng Dai 2001; Cheng Lu 2001b; Lu et al. 2000a, b), it is generally believed that energetic fireballs should be involved, where baryons are eventually accelerated to ultra-relativistic speed (Wu et al. 2001). After the main burst phase, the thin ba