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[54.02] Gamma-ray burst early optical afterglow: implications for the initial Lorentz factor and the central engine

B. Zhang, S. Kobayashi, P. Meszaros (Pennsylvania State University)

Early optical afterglows have been observed from GRB 990123, GRB 021004, and GRB 021211, which reveal rich emission features attributed to reverse shocks. It is expected that Swift will discover many early afterglows. We introduce a straightforward recipe for directly constraining the initial Lorentz factor of the fireball using the combined forward and reverse shock optical afterglow data. The scheme is largely independent of the shock microphysics. We identify two types of combinations of the reverse and forward shock emission, and explore their parameter regimes. We also discuss a possible diagnostic for magnetized ejecta.

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The author(s) of this abstract have provided an email address for comments about the abstract: bzhang@astro.psu.edu

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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.