The electromagnetic model of gamma-ray bursts

Abstract

The electromagnetic model (EMM) of gamma-ray bursts (GRBs) and a contrast of its main properties and predictions with the hydrodynamic fireball model (FBM) and its magnetohydrodynamical extension are described. The EMM assumes that rotational energy of a relativistic, stellar-mass central source (black hole–accretion disk system or fast rotating neutron star) is converted into magnetic energy through a unipolar dynamo mechanism, propagated to large distances in the form of relativistic, subsonic, Poynting flux-dominated wind and is dissipated directly into emitting particles through current-driven instabilities. Thus, there is no conversion back and forth between internal and bulk energies as in the case of the fireball model. Collimating effects of magnetic hoop stresses lead to strongly non-spherical expansion and formation of jets. Long and short GRBs may develop in a qualitatively similar way, except that in the case of long burst ejecta expansion has a relatively short, non-relativistic, strongly dissipative stage inside the star. EMMs and FBMs (as well as strongly and weakly magnetized fireballs) lead to different early afterglow dynamics, before deceleration time. Finally, the models are discussed in view of latest observational data in the Swift era.