Episodic Jets as the Central Engine of Gamma-Ray Bursts
  Most Gamma-ray bursts (GRBs) have erratic light curves, which demand that the GRB central engine launches an episodic outflow. Recent Fermi observations of some GRBs indicate a lack of the thermal photosphere component as predicted by the baryonic fireball model, which suggests a magnetic origin of GRBs. In view that powerful episodic jets have been observed along with continuous jets in other astrophysical black hole systems, here we propose an intrinsically episodic, magnetically-dominated jet model for GRB central engine. Accumulation and eruption of free magnetic energy in the corona of a differentially-rotating, turbulent accretion flow around a hyperaccreting black hole lead to ejections of episodic, magnetically dominated plasma blobs. These blobs are accelerated magnetically, collide with each other at large radii, trigger rapid magnetic reconnection and turbulence, efficient particle acceleration and radiation, and power the observed episodic prompt gamma-ray emission from GRBs. 
Feng Yuan (SHAO) and Bing Zhang (UNLV)
astro-ph.HE