Relativistic MHD jets and the GRBs
  High velocity highly collimated beams of plasma -- the jets -- are known as a general phenomenon among astrophysical sources of different energy and spatial scale. The common MHD scenario of astrophysical jet formation allows to describe the different jet sources by a scaling of the jet magnetization. In this paper we apply the MHD jet theory for GRB parameters and find indeed that main features as ultra-relativistic motion and strong collimation can be explained. Others, like GRB time-variability and the bi-modal GRB duration are (yet) beyond a MHD description. 
Christian Fendt