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Accretion modes in collapsars: prospects for GRB production | William H. Lee
; Enrico Ramirez-Ruiz
; | Date: |
13 Sep 2005 | Subject: | astro-ph | Affiliation: | IAUNAM) and Enrico Ramirez-Ruiz (IAS | Abstract: | We explore low angular momentum accretion flows onto black holes formed after the collapse of massive stellar cores. In particular, we consider the state of the gas falling quasi-spherically onto stellar-mass black holes in the hypercritical regime, where the accretion rates are in the range 0.001< Mdot < 0.5 solar masses per second and neutrinos dominate the cooling. Previous studies have assumed that in order to have a black hole switch to a luminous state, the condition l >> R_g c needs to be fulfilled. We argue that flows in hyperaccreting, stellar mass disks around black holes are likely to transition to a highly radiative state when their angular momentum is just above the threshold for disk formation, l ~ 2 R_g c. In a range R_g c < l < 2R_g c, a dwarf disk forms in which gas spirals fast into the black hole without any help from horizontal viscous stresses due to general relativistic effects. For high rotation rates l > 2 R_g c, the luminosity is supplied by large, hot equatorial bubbles around the black hole. The highest neutrino luminosities are obtained for l ~2 R_g c, and this value of angular momentum also produces the most energetic neutrinos, and thus also the highest energy deposition rates. Given the preferential range of l explored in this work, we argue that, as long as l>2R_g c, low angular momentum cores may in fact be better suited for producing neutrino--driven explosions following core collapse in supernovae and gamma ray bursts. | Source: | arXiv, astro-ph/0509307 | Services: | Forum | Review | PDF | Favorites |
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