Gamma‐Ray Burst Early Optical Afterglows: Implications for the Initial Lorentz Factor and the Central Engine | Zendy

Bing Zhang | Zendy; S. Kobayashi | Zendy; P. Mészáros | Zendy

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Gamma‐Ray Burst Early Optical Afterglows: Implications for the Initial Lorentz Factor and the Central Engine

Author(s) -

Bing Zhang,

S. Kobayashi,

P. Mészáros

Publication year - 2003

Publication title -

the astrophysical journal

Language(s) - English

Resource type - Journals

SCImago Journal Rank - 2.376

H-Index - 489

eISSN - 1538-4357

pISSN - 0004-637X

DOI - 10.1086/377363

Subject(s) - gamma ray burst , afterglow , ejecta , lorentz factor , shock (circulatory) , physics , astrophysics , lorentz transformation , swift , classical mechanics , supernova , medicine

Early optical afterglows have been observed from GRB 990123, GRB 021004, andGRB 021211, which reveal rich emission features attributed to reverse shocks.It is expected that Swift will discover many more early afterglows. Here weinvestigate in a unified manner both the forward and the reverse external shockemission components, and introduce a straightforward recipe for directlyconstraining the initial Lorentz factor of the fireball using early opticalafterglow data. The scheme is largely independent of the shock microphysics. Weidentify two types of combinations of the reverse and forward shock emission,and explore their parameter regimes. We also discuss a possible diagnostic formagnetized ejecta. There is evidence that the central engine of GRB 990123 isstrongly magnetized.Comment: emulateapj style, 6 pages, 1 figure. Expanded version accepted for publication in ApJ Part

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