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American Astronomical Society, Astrophysical Journal, 2(523), p. L121-L124, 1999

DOI: 10.1086/312282

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Optical and radio observations of the afterglow from GRB 990510: evidence for a jet

Journal article published in 1999 by F. A. Harrison, Harrison Fa, J. S. Bloom, D. A. Frail, R. Sari, Frail Da, S. R. Kulkarni, S. G. Djorgovski, P. Sari, T. Axelrod, J. Mould, B. P. Schmidt, M. H. Wieringa, R. M. Wark, Ravi Subrahmanyan and other authors.
This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

We present multi-color optical and two-frequency radio observations of the bright SAX event, GRB 990510. The well-sampled optical decay, and the radio observations are both inconsistent with simple spherical afterglow models. The achromatic optical steepening and the decay of the radio afterglow both occuring at t ∼ 1 day are evidence for hydrodynamical evolution of the source, and can be most easily interpreted by models where the GRB ejecta are collimated in a jet. Employing a simple jet model to interpret the observations, we derive a jet opening angle of θo = 0.08, reducing the isotropic gamma-ray emission of 2.9 × 10 53 erg by a factor ∼ 300. If the jet interpretation is correct, we conclude that GRB observations to-date are consistent with an energy for the central source of E ∼