Early Afterglows in Wind Environments Revisited

Y. C. Zou; X. F. Wu; Z. G. Dai

doi:10.1111/j.1365-2966.2005.09411.x

paper

Early Afterglows in Wind Environments Revisited

arXiv:astro-ph/0508602 · doi:10.1111/j.1365-2966.2005.09411.x

Abstract

When a cold shell sweeps up the ambient medium, a forward shock and a reverse shock will form. We analyze the reverse-forward shocks in a wind environment, including their dynamics and emission. An early afterglow is emitted from the shocked shell, e.g., an optical flash may emerge. The reverse shock behaves differently in two approximations: relativistic and Newtonian cases, which depend on the parameters, e.g., the initial Lorentz factor of the ejecta. If the initial Lorentz factor is much less than $114 E_{53}^{1/4} Δ_{0, 12}^{- 1/4} A_{*, - 1}^{- 1/4}$ , the early reverse shock is Newtonian. This may take place for the wider of a two-component jet, an orphan afterglow caused by a low initial Lorentz factor, and so on. The synchrotron self absorption effect is significant especially for the Newtonian reverse shock case, since the absorption frequency $ν_{a}$ is larger than the cooling frequency $ν_{c}$ and the minimum synchrotron frequency $ν_{m}$ for typical parameters. For the optical to X-ray band, the flux is nearly unchanged with time during the early period, which may be a diagnostic for the low initial Lorentz factor of the ejecta in a wind environment. We also investigate the early light curves with different wind densities, and compare them with these in the ISM model.

14 pages, 7 figures, 2 tables, accepted for publication in MNRAS

Early Afterglows in Wind Environments Revisited

Abstract

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