AN ARGUMENT FOR WEAKLY MAGNETIZED, SLOWLY ROTATING PROGENITORS OF LONG GAMMA-RAY BURSTS

Using binary evolution with Case-C mass transfer, the spins of several black holes (BHs) in X-ray binaries (XBs) have been predicted and confirmed (three cases) by observations. The rotational energy of these BHs is sufficient to power up long gamma-ray bursts (GRBs) and hypernovae (HNe) and still l...

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Bibliographic Details
Published in:The Astrophysical journal 2014-01, Vol.781 (1), p.1-6
Main Author: Mendez, Enrique Moreno
Format: Article
Language:English
Subjects:
ALFVEN WAVES
Angular momentum
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
BLACK HOLES
Collapsars
COSMIC GAMMA BURSTS
Formations
Gamma ray bursts
HELIUM BURNING
HYDROGEN BURNING
KERR FIELD
MAGNETIC FIELDS
MASS TRANSFER
Phases
Progenitors (astrophysics)
ROTATION
SPIN
Stars
SUPERNOVAE
SYNCHRONIZATION
X RADIATION
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Summary:Using binary evolution with Case-C mass transfer, the spins of several black holes (BHs) in X-ray binaries (XBs) have been predicted and confirmed (three cases) by observations. The rotational energy of these BHs is sufficient to power up long gamma-ray bursts (GRBs) and hypernovae (HNe) and still leave a Kerr BH behind. However, strong magnetic fields and/or dynamo effects in the interior of such stars deplete their cores from angular momentum preventing the formation of collapsars. Thus, even though binaries can produce Kerr BHs, most of their rotation is acquired from the stellar mantle, with a long delay between BH formation and spin up. Such binaries would not form GRBs. We study whether the conditions required to produce GRBs can be met by the progenitors of such BHs. Tidal-synchronization and Alfven timescales are compared for magnetic fields of different intensities threading He stars. A search is made for a magnetic field range that allows tidal spin up all the way in to the stellar core but prevents its slow down during differential rotation phases. The energetics for producing a strong magnetic field during core collapse, which may allow for a GRB central engine, are also estimated. An observationally reasonable choice of parameters is found (B [lap] 10 super(2) G threading a slowly rotating He star) that allows Fe cores to retain substantial angular momentum. Thus, the Case-C mass-transfer binary channel is capable of explaining long GRBs. However, the progenitors must have low initial spin and low internal magnetic field throughout their H-burning and He-burning phases.
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/781/1/3