  We consider a jet-disk symbiosis model to explain Gamma Ray Bursts and their
afterglows. It is proposed that GRBs develop in a pre-existing jet. We consider
a binary system formed by a neutron star and an O/B/WR companion in which the
energy of the GRB is due to the accretion-induced collapse of the neutron star
to a black hole. The high speed in the energy flow in AGN-jets is generally
believed to be initiated by strong magnetic field coupling to the accretion
disk of the black hole. We use the same mechanism here. We assume that in this
transition a large amount of energy is anisotropically released as Poynting
flux along the polar axis. One may think of this process as a violent and rapid
twist. This energy release naturally initiates an ultrarelativistic shock wave
in the pre-existing jet. The emission microphysics are as in fireball models.
Our model has only two parameters overall, the energy in the shock along the
jet, and the fraction of this energy in energetic electrons and positrons. The
system SS433 appears to have the properties required for a GRB precursor in our
model. We show that our model can explain the initial gamma ray burst
energetics, the spectrum and temporal behaviour of the afterglows, the low
baryon load, and do all this with a modest energy budget.
