Gamma-ray bursts: Nature's brightest explosions

During the roughly 20 seconds it shines brightest, a gamma-ray burst (GRB) is over a billion times brighter, in electromagnetic radiation, than an ordinary supernova. The key difference is that GRBs emit some appreciable fraction of their kinetic energy in channeled ultra-relativistic outflows (Lorentz factor Γ > 200). Currently credible models point to rotation as the key factor required to generate the outflows. We explore here the collapse of the core a massive, rotating star to a black hole and accretion disk and the subsequent propagation of relativistic jets through the star. A variety of high energy transients may be observed based upon the energy of the jet and the angle at which the explosion is observed, but there may be a minimum energy for GRBs that last only tens of seconds.