Equal arrival time surface effects in GRB afterglows

Abstract

Due to the relativistic motion of gamma-ray burst remnant and its deceleration in the circumburst medium, the equal arrival time surface (EATS) is not spherical, but ellipsoidal. Here the EATS effects are studied numerically. A direct comparison for the cases when the effects are or are not included is presented. Generally speaking, the EATS effect slightly hardens the spectra and postpones the peak time of the afterglows, but does not change the shapes of the spectra and light curves significantly. in the cases of a density jump or an energy-injection, the effect smears out the variations in the afterglows markedly. For the rapid rebrightening observed in the optical afterglow of GRB 030329 at t ∼ 1.6 d, the energy-injection model can give a best explanation as compared with the density jump model and two-component jet model. However, the predicted rebrightening is still not as rapid as observations due to EATS effect. © 2008 American Institute of Physics.