GRB 990123: The optical flash and the fireball model

Re'em Sari*, Tsvi Piran

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

267 Scopus citations


We show that the ongoing observations of the remarkable burst GRB 990123 agree with the predictions of the fireball model. Specifically, the observations confirm the recent prediction that the reverse shock propagating into the ejecta would produce a very strong prompt optical flash. This reverse shock has also produced the 8.46 GHz radio signal, observed after 1 day. The forward shock, which is the origin of the classical afterglow, has produced the prompt X-ray signal as well as the late optical and IR emission. The observations suggest that the initial Lorentz factor of the ejecta was ̃200. Within factors of order unity, this crude model explains all current observations of GRB 990123.

Original languageAmerican English
Pages (from-to)L109-L112
JournalAstrophysical Journal
Issue number2 PART 2
StatePublished - 1 Jun 1999
Externally publishedYes

Bibliographical note

Funding Information:
This research was supported by the US-Israel BSF grant 95-328, by the Israeli Space Agency, by NASA grant NAG5-3516, and by the Sherman Fairchild Foundation. We thank E. Blackman, D. Band, and P. Kumar for helpful discussions.


  • Gamma rays: bursts
  • Hydrodynamics
  • Relativity
  • Shock waves


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