Inner Engine Shutdown from Transitions in the Angular Momentum   Distribution in Collapsars
  For the collapsar scenario to be effective in the production of Gamma Ray Bursts, the infalling star's angular momentum $J(r)$ must be larger than the critical angular momentum needed to form an accretion disk around a blackhole (BH), namely $J_{\rm crit} = 2r_{g}c$ for a Schwarzschild BH. By means of 3D SPH simulations, here we study the collapse and accretion onto black holes of spherical rotating envelopes, whose angular momentum distribution has transitions between supercritical ($J>J_{\rm crit}$) and subcritical ($J<J_{\rm crit}$) values. Contrary to results obtained in previous 2D hydrodynamical simulations, we find that a substantial amount of subcritical material fed to the accretion disk, lingers around long enough to contribute significantly to the energy loss rate. Increasing the amount of angular momentum in the subcritical material increases the time spent at the accretion disk, and only when the bulk of this subcritical material is accreted before it is replenished by a massive outermost supercritical shell, the inner engine experiences a shutdown. Once the muffled accretion disk is provided again with enough supercritical material, the shutdown will be over and a quiescent time in the long GRB produced afterwards could be observed. 
Aldo Batta and Willaim H. Lee
astro-ph.HE