New early multi-wavelength data on GRB 230328B shows afterglow with early bump and late achromatic rebrightening at ~4000 s, modeled via MCMC as forward shock plus late energy injection in a dusty S0 host with AV~0.8 and no supernova signature.
Gamma-ray burst early optical afterglows: implications for the initial Lorentz factor and the central engine
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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.
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Earliest simultaneous multi-color optical observations of GRB 230328B: from 41 seconds to the host-galaxy identification
New early multi-wavelength data on GRB 230328B shows afterglow with early bump and late achromatic rebrightening at ~4000 s, modeled via MCMC as forward shock plus late energy injection in a dusty S0 host with AV~0.8 and no supernova signature.