A jet can be understood as an angular section of a fireball with an opening angle 1. Pugliese et al. Aloy et al.
Radiation emitted by the cannonballs gives rise to GRBs.
Cannonballs expand in their rest frame with the speed of sound in a relativistic gas . The model's decisive progress is that is now fixed by basic physics rather than guesswork. This leaves no free parameters for its calculation, except that is experimentally constrained from below. The thin arrowed lines indicate the direction of the emitted radiation. In the cannonball model the vast majority of GRBs are beamed away from us, only a fraction of order is visible.