Gamma-ray burst early optical afterglows: Implications for the initial lorentz factor and the central engine

Bing Zhang, Shiho Kobayashi, Peter Mészáros

Research output: Contribution to journalArticlepeer-review

222 Scopus citations

Abstract

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 more early afterglows. Here we investigate in a unified manner both the forward and the reverse external shock emission components, and introduce a straightforward recipe for directly constraining the initial Lorentz factor of the fireball using early 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. There is evidence that the central engine of GRB 990123 is strongly magnetized.

Original languageEnglish (US)
Pages (from-to)950-954
Number of pages5
JournalAstrophysical Journal
Volume595
Issue number2 I
DOIs
StatePublished - Oct 1 2003

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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