3,721 research outputs found
Hyper-accreting black hole as GRB central engine. I: Baryon loading in GRB jets
A hyper-accreting stellar-mass black hole has been long speculated as the
best candidate of central engine of gamma-ray bursts (GRBs). Recent rich
observations of GRBs by space missions such as Swift and Fermi pose new
constraints on GRB central engine models. In this paper, we study the baryon
loading processes of a GRB jet launched from a black hole central engine. We
consider a relativistic jet powered by -annihilation or by the
Blandford-Znajek (BZ) mechanism. We consider baryon loading from a
neutrino-driven wind from a neutrino-cooling-dominated accretion flow. For a
magnetically dominated BZ jet, we consider neutron-drifting from the magnetic
wall surrounding the jet and subsequent positron capture and proton-neutron
inelastic collisions. The minumim baryon loads in both types of jet are
calculated. We find that in both cases, a more luminous jet tends to be more
baryon poor. A neutrino-driven "fireball" is typically "dirtier" than a
magnetically dominated jet, while a magnetically dominated jet can be much
cleaner. Both models have the right scaling to interpret the empirical
relation discovered recently. Since some neutrino-driven
jets have too much baryon loading as compared with the data, we suggest that at
least a good fraction of GRBs should have a magnetically dominated central
engine.Comment: 9 pages, 2 figures; Accepted for publication in Ap
Particle-number conserving analysis for the 2-quasiparticle and high- multi-quasiparticle states in doubly-odd Lu
Two-quasiparticle bands and low-lying excited high- four-, six-, and
eight-quasiparticle bands in the doubly-odd Lu are analyzed by
using the cranked shell model (CSM) with the pairing correlations treated by a
particle-number conserving (PNC) method, in which the blocking effects are
taken into account exactly. The proton and neutron Nilsson level schemes for
Lu are taken from the adjacent odd- Lu and Hf isotopes, which
are adopted to reproduce the experimental bandhead energies of the
one-quasiproton and one-quasineutron bands of these odd- Lu and Hf nuclei,
respectively. Once the quasiparticle configurations are determined, the
experimental bandhead energies and the moments of inertia of these two- and
multi-quasiparticle bands are well reproduced by PNC-CSM calculations. The
Coriolis mixing of the low- () two-quasiparticle band
of the Gallagher-Moszkowski doublet with one nucleon in the
orbital is analyzed.Comment: 8 pages, 5 figures, 2 tables, to be published at Chinese Physics
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