532 research outputs found
Neutrino Interactions in the Outflow from Gamma-Ray Burst Accretion Disks
We examine the composition of matter as it flows away from gamma ray burst
accretion disks, in order to determine what sort of nucleosynthesis may occur.
Since there is a large flux of neutrinos leaving the surface of the disk, the
electron fraction of the outflowing material will change due to charged current
neutrino interactions. We calculate the electron fraction in the wind using
detailed neutrino fluxes from every point on the disk and study a range of
trajectories and outflow conditions for several different accretion disk
models. We find that low electron fractions, conducive to making r-process
elements, only appear in outflows from disks with high accretion rates that
have a significant region both of trapped neutrinos and antineutrinos. Disks
with lower accretion rates that have only a significant region of trapped
neutrinos can have outflows with very high electron fractions, whereas the
lowest accretion rate disks with little trapping have outflow electrons
fractions of closer to one half.Comment: 11 pages, 10 figure
Nucleosynthesis of Nickel-56 from Gamma-Ray Burst Accretion Disks
We examine the prospects for producing Nickel-56 from black hole accretion
disks, by examining a range of steady state disk models. We focus on relatively
slowly accreting disks in the range of 0.05 - 1 solar masses per second, as are
thought to be appropriate for the central engines of long-duration gamma-ray
bursts. We find that significant amounts of Nickel-56 are produced over a wide
range of parameter space. We discuss the influence of entropy, outflow
timescale and initial disk position on mass fraction of Nickel-56 which is
produced. We keep careful track of the weak interactions to ensure reliable
calculations of the electron fraction, and discuss the role of the neutrinos.Comment: 10 pages, 9 figure
On the Contribution of Gamma Ray Bursts to the Galactic Inventory of Some Intermediate Mass Nuclei
Light curves from a growing number of Gamma Ray Bursts (GRBs) indicate that
GRBs copiously produce radioactive Ni moving outward at fractions of the speed
of light. We calculate nuclear abundances of elements accompanying the
outflowing Ni under the assumption that this Ni originates from a wind blown
off of a viscous accretion disk. We also show that GRB's likely contribute
appreciably to the galactic inventory of 42Ca, 45Sc, 46Ti, 49Ti, 63Cu, and may
be a principal site for the production of 64Zn.Comment: 11 pages, 1 figur
Neutrinos and the synthesis of heavy elements: the role of gravity
The synthesis of heavy elements in the Universe presents several challenges.
From one side the astrophysical site is still undetermined and on other hand
the input from nuclear physics requires the knowledge of properties of exotic
nuclei, some of them perhaps accessible in ion beam facilities. Black hole
accretion disks have been proposed as possible r-process sites. Analogously to
Supernovae these objects emit huge amounts of neutrinos. We discuss the
neutrino emission from black hole accretion disks. In particular we show the
influence that the black hole strong gravitational field has on changing the
electron fraction relevant to the synthesis of elements.Comment: 5 pages, 5 figures, Invited talk at the 15th International Symposium
on Capture Gamma-Ray Spectroscopy and Related Topics (CGS15), to appear in
EPJ Web of Conference
Nucleosynthesis in the Outflow from Gamma Ray Burst Accretion Disks
We examine the nucleosynthesis products that are produced in the outflow from
rapidly accreting disks. We find that the type of element synthesis varies
dramatically with the degree of neutrino trapping in the disk and therefore the
accretion rate of the disk. Disks with relatively high accretion rates such as
10 M_solar/s can produce very neutron rich nuclei that are found in the r
process. Disks with more moderate accretion rates can produce copious amounts
of Nickel as well as the light elements such as Lithium and Boron. Disks with
lower accretion rates such as 0.1 M_solar/s produce large amounts of Nickel as
well as some unusual nuclei such as Ti-49, Sc-45, Zn-64, and Mo-92. This wide
array of potential nucleosynthesis products is due to the varying influence of
electron neutrinos and antineutrinos emitted from the disk on the
neutron-to-proton ratio in the outflow. We use a parameterization for the
outflow and discuss our results in terms of entropy and outflow acceleration.Comment: 12 pages, 12 figures; submitted to Ap
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