  This rapporteur review summarizes results presented in Parallel Session GBT2
(Gamma Ray Burst Theory 2) on the Collapsar and Supranova Models held 25 July
2003 at the 10th Marcel Grossmann Meeting on General Relativity, Rio de
Janeiro, Brazil. A central issue in GRB studies is the process whereby energy
is released from the GRB engine. One scenario is the collapsar model, where the
evolved stellar core promptly collapses to a black hole surrounded by a
massive, intermittently-accreting torus of nuclear density material. A second
scenario is the supranova model, where the first step of a two-step collapse
process leaves behind a rapidly rotating neutron star stabilized by rotation,
which later collapses to a black hole while making the GRB. In the supranova
model, a powerful pulsar wind lasting days to weeks after the supernova makes
distinctive signatures from the heating of the supernova remnant (SNR) shell,
which should be discovered with Swift. This model also predicts nonstandard
reddened excesses from the cooling SNR due to the range of delays between the
two collapse events, contrary to observations of SN emissions from low redshift
GRBs which favor the collapsar model. The observational basis for both models
is critically reviewed. An outline of a GRB model is proposed where the second
collapse takes place within minutes to hours after the primary SN event, during
which time loss of centrifugal support along the rotation axis of the neutron
star provides a relatively baryon-clean polar environment along which a newly
formed, rapidly spinning black hole drives collimated baryon-dilute outflows.
