paper

Optical and Radio Observations of the Afterglow from GRB990510: Evidence for a Jet

arXiv:astro-ph/9905306 · doi:10.1086/312282

Abstract

We present multi-color optical and two-frequency radio observations of the bright SAX event, GRB 990510. The well-sampled optical decay, together with the radio observations are inconsistent with simple spherical afterglow models. The achromatic optical steepening and the decay of the radio afterglow both occuring at 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 , reducing the isotropic gamma-ray emission of erg by a factor . If the jet interpretation is correct, we conclude that GRB observations to-date are consistent with an energy for the central source of $E \lsim 10^{52}$ erg.

12 pages, 2 figures. Version accepted for publication in ApJ Letters

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