  The physics of gamma-ray bursts (GRBs) and their offsets from the centers of
their host galaxies are used to investigate the evolutionary state of their
progenitors, motivated by the popular idea that GRBs are linked with the
cataclysmic collapse of massive stars. We suggest that GRB progenitors in the
inner and outer regions of hosts may be intrinsically different: outer bursts
appear to have systematically greater isotropic equivalent energies (or
narrower jets). This may provide an interesting clue to the nature of GRBs, and
could reflect a relation between metallicity and the evolution of GRB
progenitors. If true, then this offset-isotropic luminosity correlation is a
strong argument for a collapsar origin of long-duration GRBs.
