On the Optical Light Curves of Afterglows from Jetted Gamma-ray Burst Ejecta: Effects of Parameters

Y. F. Huang; Z. G. Dai; T. Lu

doi:10.1046/j.1365-8711.2000.03683.x

paper

On the Optical Light Curves of Afterglows from Jetted Gamma-ray Burst Ejecta: Effects of Parameters

arXiv:astro-ph/0005549 · doi:10.1046/j.1365-8711.2000.03683.x

Abstract

Due to some refinements in the dynamics, we can follow the overall evolution of a realistic jet numerically till its bulk velocity being as small as $β c \sim 1 0^{- 3} c$ . We find no obvious break in the optical light curve during the relativistic phase itself. However, an obvious break does exist at the transition from the relativistic phase to the non-relativistic phase, which typically occurs at time $t \sim 1 0^{6}$ --- $1 0^{6.5}$ s (i.e., 10 --- 30 d). The break is affected by many parameters, such as the electron energy fraction $ξ_{e}$ , the magnetic energy fraction $ξ_{B}^{2}$ , the initial half opening angle $θ_{0}$ , and the medium number density $n$ . Increase of any of them to a large enough value will make the break disappear. Although the break itself is parameter-dependent, afterglows from jetted GRB remnants are uniformly characterized by a quick decay during the non-relativistic phase, with power law timing index $α \geq 2.1$ . This is quite different from that of isotropic fireballs, and may be of fundamental importance for determining the degree of beaming in $γ$ -ray bursts observationally.

arXiv comment8 pages, 10 embedded eps figures, MNRAS in press, using epsfig.sty and mn.sty

On the Optical Light Curves of Afterglows from Jetted Gamma-ray Burst Ejecta: Effects of Parameters

Abstract

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