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Session 33 - Gamma-ray Burst Counterparts and Afterglows.
Topical, Oral session, Tuesday, June 09

[33.12] The Radio Afterglows of Gamma-Ray Bursts

G. B. Taylor (National Radio Astronomy Observatory)

Radio emission from GRBs is expected in the relativistic fireball models as the blastwave encounters the external medium. Once produced, the radio emission will be difficult to extinguish as it propagates outward. This, combined with the relatively low background source density on the sky at centimeter wavelengths, should make radio observations one of the best ways to identify GRB afterglows (provided that the GRBs can be rapidly localized to within the relatively small field of view of most radio telescopes). Yet radio counterparts have only been detected for 2 GRBs with good initial localizations. If present, radio observations of the GRB afterglow can yield estimates of the size and expansion velocity of the fireball via both analysis of the variability induced by interstellar scattering, and analysis of the changing spectral shape with time. Very Long Baseline Interferometry (VLBI) observations, besides confirming the compact size of the afterglow, can be used to place lower limits on the distance to a radio-loud GRB. I will summarize what we've learned from radio observations of GRBs, with emphasis on the two GRBs with detected radio afterglows: G970508 and G980329.

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