6,374 research outputs found
X-ray emission from the PSR B1259--63 system near apastron
The PSR B1259--63 system contains a 47 ms radio pulsar in a highly eccentric
binary with a Be-star companion. Strongly time variable X-ray emission was
reported from this system as the pulsar was near apastron in 1992-early 1993.
The variability was primarily deduced from an apparent non-detection of the
\psr system during a first pre-apastron \ros observation in February~1992. We
have re-analyzed the \ros observations of the \psr system. Contrary to the
results of a previous analysis, we find that the \psr system was detected by
\ros during the first off-axis February~1992 observation. The intensity of the
soft X-ray emission of the \psr system before and after the 1992 apastron
appears to vary at most by a factor . Our results sensibly constrain
theoretical models of X-ray emission from the \psr system.Comment: LATEX, Accepted for publ. in ApJ
On the stability of Bose-Fermi mixtures
We consider the stability of a mixture of degenerate Bose and Fermi gases.
Even though the bosons effectively repel each other the mixture can still
collapse provided the Bose and Fermi gases attract each other strongly enough.
For a given number of atoms and the strengths of the interactions between them
we find the geometry of a maximally compact trap that supports the stable
mixture. We compare a simple analytical estimation for the critical axial
frequency of the trap with results based on the numerical solution of
hydrodynamic equations for Bose-Fermi mixture.Comment: 4 pages, 3 figure
Ray-tracing in pseudo-complex General Relativity
Motivated by possible observations of the black hole candidate in the center
of our galaxy and the galaxy M87, ray-tracing methods are applied to both
standard General Relativity (GR) and a recently proposed extension, the
pseudo-complex General Relativity (pc-GR). The correction terms due to the
investigated pc-GR model lead to slower orbital motions close to massive
objects. Also the concept of an innermost stable circular orbit (ISCO) is
modified for the pc-GR model, allowing particles to get closer to the central
object for most values of the spin parameter than in GR. Thus, the
accretion disk, surrounding a massive object, is brighter in pc-GR than in GR.
Iron K emission line profiles are also calculated as those are good
observables for regions of strong gravity. Differences between the two theories
are pointed out.Comment: revised versio
Probing Pair-Correlated Fermionic Atoms through Correlations in Atom Shot Noise
Pair-correlated fermionic atoms are created through dissociation of weakly
bound molecules near a magnetic-field Feshbach resonance. We show that
correlations between atoms in different spin states can be detected using the
atom shot noise in absorption images. Furthermore, using time-of-Flight imaging
we have observed atom pair correlations in momentum space
Monte Carlo aided design of the inner muon veto detectors for the Double Chooz experiment
The Double Chooz neutrino experiment aims to measure the last unknown
neutrino mixing angle theta_13 using two identical detectors positioned at
sites both near and far from the reactor cores of the Chooz nuclear power
plant. To suppress correlated background induced by cosmic muons in the
detectors, they are protected by veto detector systems. One of these systems is
the inner muon veto. It is an active liquid scintillator based detector and
instrumented with encapsulated photomultiplier tubes. In this paper we describe
the Monte Carlo aided design process of the inner muon veto, that resulted in a
detector configuration with 78 PMTs yielding an efficiency of 99.978 +- 0.004%
for rejecting muon events and an efficiency of >98.98% for rejecting correlated
events induced by muons. A veto detector of this design is currently used at
the far detector site and will be built and incorporated as the muon
identification system at the near site of the Double Chooz experiment
Colour-singlet strangelets at finite temperature
Considering massless and quarks, and massive (150 MeV) quarks in
a bag with the bag pressure constant MeV, a colour-singlet
grand canonical partition function is constructed for temperatures
MeV. Then the stability of finite size strangelets is studied minimizing the
free energy as a function of the radius of the bag. The colour-singlet
restriction has several profound effects when compared to colour unprojected
case: (1) Now bulk energy per baryon is increased by about MeV making the
strange quark matter unbound. (2) The shell structures are more pronounced
(deeper). (3) Positions of the shell closure are shifted to lower -values,
the first deepest one occuring at , famous -particle ! (4) The shell
structure at vanishes only at MeV, though for higher
-values it happens so at MeV.Comment: Revtex file(8 pages)+6 figures(ps files) available on request from
first Autho
Adiabatic loading of a Bose-Einstein condensate in a 3D optical lattice
We experimentally investigate the adiabatic loading of a Bose-Einstein
condensate into an optical lattice potential. The generation of excitations
during the ramp is detected by a corresponding decrease in the visibility of
the interference pattern observed after free expansion of the cloud. We focus
on the superfluid regime, where we show that the limiting time scale is related
to the redistribution of atoms across the lattice by single-particle tunneling
Superdeformation and clustering in Ca studied with Antisymmetrized Molecular Dynamics
Deformed states in Ca are investigated with a method of
antisymmetrized molecular dynamics. Above the spherical ground state,
rotational bands arise from a normal deformation and a superdeformation as well
as an oblate deformation. The calculated energy spectra and transition
strengths in the superdeformed band reasonably agree to the experimental data
of the superdeformed band starting from the state at 5.213 MeV. By the
analysis of single-particle orbits, it is found that the superdeformed state
has particle-hole nature of an - configuration. One of new findings is
parity asymmetric structure with C+Si-like clustering in the
superdeformed band. We predict that C+Si molecular bands may be
built above the superdeformed band due to the excitation of inter-cluster
motion. They are considered to be higher nodal states of the superdeformed
state. We also suggest negative-parity bands caused by the parity asymmetric
deformation.Comment: 13 figures, submitted to Phys. Rev.
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