Issue |
A&A
Volume 388, Number 1, June II 2002
|
|
---|---|---|
Page(s) | 189 - 201 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20020415 | |
Published online | 28 May 2002 |
Baryonic pollution in gamma-ray bursts: The case of a magnetically driven wind emitted from a disk orbiting a stellar mass black hole
1
Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str 1, Postfach 1317, 85741 Garching bei München, Germany
2
Institut d'Astrophysique de Paris, 98bis Bld. Arago, 75014 Paris, France
Corresponding author: F. Daigne, daigne@discovery.saclay.cea.fr
Received:
15
October
2001
Accepted:
25
February
2002
Most models for the central engine of gamma-ray bursts involve a stellar mass
black hole surrounded by a thick disk formed after the merging of a
system of compact objects or the collapse of a massive star.
Energy released from the accretion of disk material by the black hole or
from the rotation of the hole itself extracted by the Blandford-Znajek
mechanism powers a relativistic wind along the system axis.
Lorentz factors of several hundreds are needed to solve the compactness
problem in the wind which implies the injection
of a tremendous
power into a very small
amount of
matter. The Blandford-Znajek mechanism, where the outflow follows magnetic
field lines anchored to the black hole is probably the best way to prevent
baryonic pollution and can even initially produce a purely leptonic wind.
In this paper we rather study the wind emitted from the inner part of the
disk where
the risk of baryonic pollution is much larger since the outflow originates
from high density regions. We show that the
baryonic load of this wind sensitively depends on the disk temperature and
magnetic field geometry and that the outflow can become ultra-relativistic
(Lorentz
factor ) under quite restrictive conditions only.
Conversely, if Γ remains of the order of unity the dense wind emitted
from the
inner disk could help to confine the central jet but may also represent a
source of baryon contamination for the Blandford-Znajek
mechanism.
Key words: gamma rays: bursts / accretion: accretion disks / magnetohydrodynamics (MHD) / neutrinos / relativity
© ESO, 2002
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