Can Neutrino‐cooled Accretion Disks Be an Origin of Gamma‐Ray Bursts?

It is often considered that a massive torus with solar mass or so surroundinga stellar-mass black hole may be a central engine of a gamma-ray burst. Westudy the properties of such massive accretion tori (or disks) based on the$\alpha$ viscosity model. For surface density exceeding about $10^{20}$ gcm$^{-2}$, which realizes when about a solar-mass material is contained withina disk with a size of $\sim 5 \times 10^6$ cm, we find that (1) luminosity ofphotons is practically zero due to significant photon trapping, (2) neutrinocooling dominates over advective cooling, (3) pressure of degenerate electronsdominates over pressure of gas and photons, and (4) magnetic field strengthexceeds the critical value of about $4 \times 10^{13}$ G, even if we take 0.1 %of the equi-partition value. The possible observable quantum electrodynamical(QED) effects arising from super-critical fields are discussed. Mostinterestingly, photon splitting may occur, producing significant number ofphotons of energy below $\sim 511$ keV, thereby possibly suppressing e$^\pm$pair creation.Comment: 24 pages, 5 postscript figures, to appear in Ap