Dessart 2007 Proto-NS phase for GRBs and Hypernovae

主要内容:
fast rotation in the iron core may inhibit

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文章信息:

arXiv:0710.5789 [ps, pdf, other]

Title: The Proto-neutron Star Phase of the Collapsar Model and the Route to Long-soft Gamma-ray Bursts and Hypernovae

Authors: Luc Dessart, Adam Burrows, Eli Livne, Christian Ott

Comments: 5 pages, 1 table, 3 figures, submitted to ApJL

Subjects: Astrophysics (astro-ph)

Recent stellar evolutionary calculations of low-metallicity massive fast-rotating main-sequence stars yield iron cores at collapse endowed with high angular momentum. It is thought that high angular momentum and black hole formation are critical ingredients of the collapsar model of long-soft GRBs. Here, we present 2D multi-group, flux-limited-diffusion MHD simulations of the collapse, bounce, and immediate post-bounce phases of a 35Msun collapsar-candidate model of Woosley & Heger. We find that, provided the magneto-rotational instability (MRI) operates in the differentially-rotating surface layers of the millisecond-period proto-neutron star (PNS), a magnetically-driven explosion ensues during the PNS phase, in the form of a baryon-loaded non-relativistic jet, and that a black hole, central to the collapsar model, does not form. Paradoxically, and although much uncertainty surrounds mass loss, angular momentum transport, magnetic fields, and the MRI, current models of chemically homogeneous evolution at low metallicity yield massive stars with iron cores that may have too much angular momentum to avoid a magnetically-driven, hypernova-like, explosion in the immediate post-bounce phase that does not lead to black hole formation. We surmise that fast rotation in the iron core may inhibit, rather than enable, collapsar formation, which requires a large angular momentum not in the core but above it. Variations in the angular momentum distribution of massive stars at core collapse might provide an explanation both for the diversity of Type Ic supernovae/hypernovae and for when they are associated with a GRB. A corollary is that, rather than the progenitor mass, the angular momentum distribution, through its effect on magnetic field amplification, distinguishes these outcomes.