Li-Xin Li

Two most important problems for gamma-ray bursts (GRBs) are how to generate an enormous amount of energy up to 10⁵⁴ ergs, and how to make the energy clean enough (i.e. with less load of baryons) for providing a huge bulk Lorentz factor >300. The former is required by explaining the luminosity of GRBs, the later is required by understanding the rapid variability of the luminosity and the non-thermal feature of the spectrum.

This cross-sectional diagram shows a tokamak model for GRBs. A toroidal electric current flows on the surface of a dense plasma torus (the purple regions) spinning around a Kerr black hole (the black sphere), which generates a poloidal magnetic field outside the torus. The toroidal current flows out of the page on the left (indicated with thick dots), into the page on the right (indicated with cross signs). The poloidal magnetic field lines are shown with solid curves. On the surface of the torus the magnetic field is parallel to the surface. The closed magnetic field lines winding around the torus compress and confine the plasma in the torus, as in the case of tokamaks in controlled nuclear fusion. If the magnetic field is strong enough (typically 10¹⁵ Gauss or higher for GRBs), the baryonic contamination from the plasma in the torus is greatly suppressed and a clean magnetosphere of electron-positron pairs is built up around the black hole. If some magnetic field lines threading the black hole are open and connect with loads, clean energy can be extracted from the Kerr black hole by the Blandford-Znajek mechanism. The energy extracted from the black hole is converted into the kinetic energy of the electron-positron pairs in the magnetosphere around the black hole, which generates two oppositely directed jets (the red regions) of electron-positron pairs with super-high bulk Lorentz factors. The jets collide and interact with the interstellar medium, which produces gamma-ray bursts and the afterglows. For details see L. -X. Li, ApJ 544, 375 (2000).

This model may even explain the recently observed connection between GRBs and supernovae (B. Paczynski astro-ph/9909048 and references therein). As the plasma in the torus is heated by the compression caused by the magnetic field winding around the torus its temperature and pressure will increase. If the internal temperature reaches the ignition temperature of the nuclear fuel in the torus, nuclear fusion starts which may produce an explosion like a supernova.