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28 March 2024
 
  » arxiv » astro-ph/0509307

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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
AffiliationIAUNAM) and Enrico Ramirez-Ruiz (IAS
AbstractWe 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
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