No Radio Afterglow from the Gamma-Ray Burst of 1997 February 28

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Abstract
We present radio observations of the gamma-ray burster GRB 970228 made with the Very Large Array and the Owens Valley Radio Observatory which span a range of postburst timescales from 1 to 300 days. A search for a time-variable radio source was conducted covering an area that included a fading X-ray source and an optical transient, both of which are thought to be the long-wavelength counterparts to the gamma-ray burst. At the position of the optical transient, sensitive limits between 10 μJy and 1 mJy can be placed on the absence of a radio counterpart to GRB 970228 between 1.4 and 240 GHz. We apply a simple formulation of a fireball model which has been used with some success to reproduce the behavior of the optical and X-ray light curves. Using this model, we conclude that the radio nondetections are consistent with the peak flux density of the afterglow lying between 20 and 40 μJy, and it requires that the optical flux peaked between 4 and 16 hr after the burst.
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