Astron. Astrophys. Suppl. Ser. 138, 539-540
J.E. Rhoads
Kitt Peak National Observatory, NOAO, P.O. Box 26732, Tucson, AZ 85726-6732, U.S.A.
e-mail: rhoads@noao.edu
Received December 24, 1998; accepted April 29, 1999
The beaming angle 
is the main uncertainty in gamma ray burst
energy requirements today.
We summarize predictions for the light curves of beamed bursts, and
model the R band light curve of GRB 970508 to derive
. This yields an irreducible minimum energy requirement
of 
ergs to power the afterglow alone.
Key words: gamma-ray: bursts
Copyright The European Southern Observatory (ESO)