2 research outputs found
Optical and Radio Observations of the Afterglow from GRB990510: Evidence for a Jet
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.Comment: 12 pages, 2 figures. Version accepted for publication in ApJ Letter