Journal
ASTROPHYSICAL JOURNAL
Volume 765, Issue 2, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/765/2/125
Keywords
accretion, accretion disks; black hole physics; magnetic fields
Categories
Funding
- NSF [AST-0908362]
- National Natural Science Foundation of China [11003004, 11025313, 11173011, U1231101]
- National Basic Research Program (973 Program) of China [2009CB824800]
- China Scholarship Program
- Cheung Kong Scholar fellowship at Peking University in China
- Division Of Astronomical Sciences
- Direct For Mathematical & Physical Scien [0908362] Funding Source: National Science Foundation
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A hyperaccreting stellar-mass black hole has been long speculated as the best candidate for the 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 nu(nu) over bar -annihilation or by the Blandford-Znajek (BZ) mechanism. We consider baryon loading from a neutrino-driven wind launched 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 minimum 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 Gamma-L-iso 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.
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