Astronomy

Every Burst Is Not the Same

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Science  21 Jul 2000:
Vol. 289, Issue 5478, pp. 361-363
DOI: 10.1126/science.289.5478.361e

The standard model of gamma ray bursts (GRBs) and the subsequent afterglow (in the x-ray to radio wave spectrum) is that an exploding fireball creates a shock wave that is driven into the interstellar medium (ISM). Synchrotron emission from electrons that are accelerated in this relativistic blast wave interact with a constant-density ISM to produce the observed flux and decay of emissions through a range of wavelengths.

Chevalier and Li have used the latest observations to refine the standard model and to revise their alternative model. In their model, a massive progenitor star still explodes initially, but the afterglows are produced by expansion of the blast wave into the stellar wind of the progenitor star rather than the ISM. Their model is consistent with a rapid fading of the optical emission, the association of GRBs with supernovae, and high estimated densities in radio emissions. The revised ISM model fits with observations of bright optical flashes related to reverse shock waves and other flux and emission characteristics that are different from the GRBs associated with the stellar wind model. Thus, the ISM model is applicable to GRBs whose progenitors are the mergers of compact stars while the stellar wind model fits those GRBs that form through the explosion of a massive star (such as a Wolf-Rayet star). — LR

Astrophys. J., in press [astro-ph/9908272].

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