High-resolution simulations demonstrate that two-zone models for GRB early afterglows fail to match hydrodynamic evolution in the Newtonian reverse shock regime before Blandford-McKee self-similarity, causing systematic overpredictions of emission depending on the transition prescription.
Predictions for The Very Early Afterglow and The Optical Flash
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abstract
According to the internal-external shocks model for $\gamma $-ray bursts (GRBs), the GRB is produced by internal shocks within a relativistic flow while the afterglow is produced by external shocks with the ISM. We explore the early afterglow emission. For short GRBs the peak of the afterglow will be delayed, typically, by few dozens of seconds after the burst. For long GRBs the early afterglow emission will overlap the GRB signal. We calculate the expected spectrum and the light curves of the early afterglow in the optical, X-ray and $\gamma $-ray bands. These characteristics provide a way to discriminate between late internal shocks emission (part of the GRB) and the early afterglow signal. If such a delayed emission, with the characteristics of the early afterglow, will be detected it can be used both to prove the internal shock scenario as producing the GRB, as well as to measure the initial Lorentz factor of the relativistic flow. The reverse shock, at its peak, contains energy which is comparable to that of the GRB itself, but has a much lower temperature than that of the forward shock so it radiates at considerably lower frequencies. The reverse shock dominates the early optical emission, and an optical flash brighter than 15th magnitude, is expected together with the forward shock peak at x-rays or $\gamma$-rays. If this optical flash is not observed, strong limitations can be put on the baryonic contents of the relativistic shell deriving the GRBs, leading to a magnetically dominated energy density.
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astro-ph.HE 2years
2026 2verdicts
UNVERDICTED 2representative citing papers
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.
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Systematic Error in Approximate Models of the GRB Early Afterglow
High-resolution simulations demonstrate that two-zone models for GRB early afterglows fail to match hydrodynamic evolution in the Newtonian reverse shock regime before Blandford-McKee self-similarity, causing systematic overpredictions of emission depending on the transition prescription.
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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.