Cannonballs in the context of gamma ray bursts: Formation sites?

We investigate possible formation sites of the cannonballs (in the gamma ray bursts context) by calculating their physical parameters, such as density, magnetic field, and temperature close to the origin. Our results favor scenarios where the cannonballs form as instabilities (knots) within magnetized jets from hyperaccreting disks. These instabilities would most likely set in beyond the light cylinder where flow velocity with Lorentz factors as high as 2000 can be achieved. The cannonball model for gamma ray bursts requires that cannonballs form inside core-collapse supernovae. Our findings challenge the cannonball model of gamma ray bursts, unless hyperaccreting disks and the corresponding jets are common occurrences in core-collapse SNe.