SIMBAD references

The MeV radiation front of gamma-ray bursts creates copious e^± pairs as it propagates through an ambient medium. The created pairs enrich the leptonic component of the medium by a large factor at distances R<R_load∼10¹⁶ cm from the burst center. The following blast wave sweeps up the pair-rich medium and then emits the observed afterglow radiation. We find that the afterglow has a ``memory'' of e<sup>±</sup> loading outside R<sub>load</sub>. The e<sup>±</sup> remain in the swept-up material and slowly cool down by emitting synchrotron radiation. They are likely to dominate the blast wave emission in IR, optical, and UV bands during the first minutes of the observed afterglow. The e<sup>±</sup> afterglow is described by a simple formula, which is derived analytically and checked by numerical integration of synchrotron emission over the blast material; a suitable Lagrangian formalism is developed for such calculations. The main signature of e<sup>±</sup> radiation is its flat (``white'') spectrum in a broad range of frequencies from IR to UV and possibly soft X-rays. This radiation can be detected by the Swift satellite, which would enable new observational tests for the explosion physics.