Open AccessEarly afterglows in wind environments revisited
Author(s) -
Zou Y. C.,
Wu X. F.,
Dai Z. G.
Publication year - 2005
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2005.09411.x
Subject(s) - physics , ejecta , lorentz factor , afterglow , astrophysics , shock (circulatory) , light curve , gamma ray burst , interstellar medium , absorption (acoustics) , astronomy , lorentz transformation , supernova , galaxy , optics , classical mechanics , medicine
When a cold shell sweeps up the ambient medium, a forward shock and a reverse shock will form. We analyse 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: the 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 1/4 53 Δ −1/4 0,12 A −1/4 *,−1 , 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, as 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 those in the interstellar medium model.