  Long-duration gamma-ray bursts (GRBs) are widely believed to be
highly-collimated explosions (opening angle theta ~ 1-10 deg). As a result of
this beaming factor, the true energy release from a GRB is usually several
orders of magnitude smaller than the observed isotropic value. Measuring this
opening angle, typically inferred from an achromatic steepening in the
afterglow light curve (a "jet" break), has proven exceedingly difficult in the
Swift era. Here we undertake a study of five of the brightest (in terms of the
isotropic prompt gamma-ray energy release, E(gamma, iso)) GRBs in the Swift era
to search for jet breaks and hence constrain the collimation-corrected energy
release. We present multi-wavelength (radio through X-ray) observations of GRBs
050820A, 060418, and 080319B, and construct afterglow models to extract the
opening angle and beaming-corrected energy release for all three events.
Together with results from previous analyses of GRBs 050904 and 070125, we find
evidence for an achromatic jet break in all five events, strongly supporting
the canonical picture of GRBs as collimated explosions. The most natural
explanation for the lack of observed jet breaks from most Swift GRBs is
therefore selection effects. However, the opening angles for the events in our
sample are larger than would be expected if all GRBs had a canonical energy
release of ~ 10e51 erg. The total energy release we measure for those
"hyper-energetic" (E(total) >~ 10e52 erg) events in our sample is large enough
to start challenging models with a magnetar as the compact central remnant.
