837 research outputs found
A "kilonova" associated with short-duration gamma-ray burst 130603B
Short-duration gamma-ray bursts (SGRBs) are intense flashes of cosmic
gamma-rays, lasting less than ~2 s, whose origin is one of the great unsolved
questions of astrophysics today. While the favoured hypothesis for their
production, a relativistic jet created by the merger of two compact stellar
objects (specifically, two neutron stars, NS-NS, or a neutron star and a black
hole, NS-BH), is supported by indirect evidence such as their host galaxy
properties, unambiguous confirmation of the model is still lacking. Mergers of
this kind are also expected to create significant quantities of neutron-rich
radioactive species, whose decay should result in a faint transient in the days
following the burst, a so-called "kilonova". Indeed, it is speculated that this
mechanism may be the predominant source of stable r-process elements in the
Universe. Recent calculations suggest much of the kilonova energy should appear
in the near-infrared (nIR) due to the high optical opacity created by these
heavy r-process elements. Here we report strong evidence for such an event
accompanying SGRB 130603B. If this simplest interpretation of the data is
correct, it provides (i) support for the compact object merger hypothesis of
SGRBs, (ii) confirmation that such mergers are likely sites of significant
r-process production and (iii) quite possibly an alternative, un-beamed
electromagnetic signature of the most promising sources for direct detection of
gravitational waves.Comment: preprint of paper appearing in Nature (3 Aug 2013
An optimized chiral nucleon-nucleon interaction at next-to-next-to-leading order
We optimize the nucleon-nucleon interaction from chiral effective field
theory at next-to-next- to-leading order. The resulting new chiral force
NNLOopt yields \chi^2 \approx 1 per degree of freedom for laboratory energies
below approximately 125 MeV. In the A = 3, 4 nucleon systems, the contributions
of three-nucleon forces are smaller than for previous parametrizations of
chiral interactions. We use NNLOopt to study properties of key nuclei and
neutron matter, and demonstrate that many aspects of nuclear structure can be
understood in terms of this nucleon-nucleon interaction, without explicitly
invoking three-nucleon forces.Comment: 6 pages, 4 figure
In Memoriam: Professor Emeritus Richard O. Kummert
The Washington Law Review dedicates its October 2012 issue to Professor Richard O. Kummert who passed away last April at the age of seventy-nine. Professor Kummert served as the faculty advisor to the Washington Law Review for over four decades. The success of this publication owes, in many ways, to Professor Kummert\u27s steadfast guidance. The following memorial remarks come from his former students, colleagues, and friends. Many, but not all, of these remarks have been graciously adapted from speeches given at Professor Kummert\u27s memorial service, which was held at the University of Washington School of Law on April 29, 2012
Modern meson--exchange potential and superfluid neutron star crust matter
In this work we study properties of neutron star crusts, where matter is
expected to consist of nuclei surrounded by superfluid neutrons and a
homogeneous background of relativistic electrons. The nuclei are disposed in a
Coulomb lattice, and it is believed that the structure of the lattice
influences considerably the specific heat of the neutronic matter inside the
crust of a neutron star. Using a modern meson--exchange potential in the
framework of a local--density approximation we calculate the neutronic specific
heat accounting for various shapes of the Coulomb lattice, from spherical to
non--spherical nuclear shapes. We find that a realistic nucleon--nucleon
potential leads to a significant increase in the neutronic specific heat with
respect to that obtained assuming a uniform neutron distribution. The increase
is largest for the non--spherical phase of the crust. These results may have
consequences for the thermal history of young neutron stars.Comment: Revtex, 5 pages, 4 figures included as uuencoded p
The optical afterglow of the short gamma-ray burst GRB 050709
It has long been known that there are two classes of gamma-ray bursts (GRBs),
mainly distinguished by their durations. The breakthrough in our understanding
of long-duration GRBs (those lasting more than ~2 s), which ultimately linked
them with energetic Type Ic supernovae, came from the discovery of their
long-lived X-ray and optical afterglows, when precise and rapid localizations
of the sources could finally be obtained. X-ray localizations have recently
become available for short (duration <2 s) GRBs, which have evaded optical
detection for more than 30 years. Here we report the first discovery of
transient optical emission (R-band magnitude ~23) associated with a short
burst; GRB 050709. The optical afterglow was localized with subarcsecond
accuracy, and lies in the outskirts of a blue dwarf galaxy. The optical and
X-ray afterglow properties 34 h after the GRB are reminiscent of the afterglows
of long GRBs, which are attributable to synchrotron emission from
ultrarelativistic ejecta. We did not, however, detect a supernova, as found in
most nearby long GRB afterglows, which suggests a different origin for the
short GRBs.Comment: 11 pages, 3 figures, press material at http://www.astro.ku.dk/dark
Living on the edge of stability, the limits of the nuclear landscape
A first-principles description of nuclear systems along the drip lines
presents a substantial theoretical and computational challenge. In this paper,
we discuss the nuclear theory roadmap, some of the key theoretical approaches,
and present selected results with a focus on long isotopic chains. An important
conclusion, which consistently emerges from these theoretical analyses, is that
three-nucleon forces are crucial for both global nuclear properties and
detailed nuclear structure, and that many-body correlations due to the coupling
to the particle continuum are essential as one approaches particle drip lines.
In the quest for a comprehensive nuclear theory, high performance computing
plays a key role.Comment: Contribution to proceedings of Nobel Symposium 152: Physics with
radioactive beams, June 2012, Gothenburg, Swede
Brewing of filter coffee
We report progress on mathematical modelling of coffee grounds in a drip filter coffee machine. The report focuses on the evolution of the shape of the bed of coffee grounds during extraction with some work also carried out on the chemistry of extraction. This work was sponsored by Philips who are interested in understanding an observed correlation between the final shape of the coffee grounds and the quality of the coffee. We used experimental data gathered by Philips and ourselves to identify regimes in the coffee brewing process and relevant regions of parameter space. Our work makes it clear that a number of separate processes define the shape of the coffee bed depending on the values of the parameters involved e.g. the size of the grains and the speed of fluid flow during extraction. We began work on constructing mathematical models of the redistribution of the coffee grounds specialised to each region and on a model of extraction. A variety of analytic and numerical tools were used. Furthermore our research has progressed far enough to allow us to begin to exploit connections between this problem and other areas of science, in particular the areas of sedimentology and geomorphology, where the processes we have observed in coffee brewing have been studied
Large-basis shell-model calculation of 10C->10B Fermi matrix element
We use a shell-model calculation with a two-body effective
interaction derived microscopically from the Reid93 potential to calculate the
isospin-mixing correction for the 10C->10B superallowed Fermi transition. The
effective interaction takes into account the Coulomb potential as well as the
charge dependence of T=1 partial waves. Our results suggest the isospin- mixing
correction , which is compatible with previous
calculations. The correction obtained in those calculations, performed in a
space, was dominated by deviation from unity of the radial
overlap between the converted proton and the corresponding neutron. In the
present calculation this effect is accommodated by the large model space. The
obtained correction is about a factor of four too small to obtain
unitarity of the Cabibbo-Kobayashi-Maskawa matrix with the present experimental
data.Comment: 14 pages. REVTEX. 3 PostScript figure
Z=50 shell gap near Sn from intermediate-energy Coulomb excitations in even-mass Sn isotopes
Rare isotope beams of neutron-deficient Sn nuclei from the
fragmentation of Xe were employed in an intermediate-energy Coulomb
excitation experiment yielding transition strengths.
The results indicate that these values are much larger
than predicted by current state-of-the-art shell model calculations. This
discrepancy can be explained if protons from within the Z = 50 shell are
contributing to the structure of low-energy excited states in this region. Such
contributions imply a breaking of the doubly-magic Sn core in the light
Sn isotopes.Comment: 4 pages, 4 figure
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