95 research outputs found
Pulsars With Jets May Harbor Dynamically Important Accretion Disks
For many astrophysical sources with jets, there is evidence for the
contemporaneous presence of disks. In contrast, pulsars such as the Crab and
Vela show jets but have not yet revealed direct evidence for accretion disks.
Here we show that for such pulsars, an accretion disk radiating below
detectable thresholds may simultaneously account for (1) observed deviations in
the braking indices from that of the simple dipole, (2) observed pulsar timing
ages, and (3) possibly even the jet morphology via a disk outflow that
interacts with the pulsar wind within, collimating and/or redirecting it.Comment: 10 pages, 2 figs., in press, ApJ. Let
Quark Matter in Neutron Star Mergers
Binary neutron star mergers are expected to be one of the most promising
source of gravitational waves (GW) for the network of laser interferometric and
bar detectors becoming operational in the next few years. The merger wave
signal is expected to be sensitive to the interior structure of the neutron
star (NS). The structure of high density phases of matter is under current
experimental investigation in heavy-ion collisions. We investigate the
dependence of the merger process and its GW signal on the presence of quarks in
these phases by performing numerical simulations, where the smoothed particle
hydrodynamics (SPH) method and the conformally flat approximation for the
3-geometry in general relativistic gravity are implemented.Comment: 4 Pages, 4 Figures, Proc. Nuclei in the Cosmos 7, 200
Mapping Deconfinement with a Compact Star Phase Diagram
We have found correlations between properties of the equation of state for
stellar matter with a phase transition at supernuclear densities and two
characteristic features of a "phase diagram" for rotating compact stars in the
angular velocity - baryon number plane: 1) the critical dividing line between
mono- and two-phase star configurations and 2) the maximum mass line. The
second line corresponds to the minimum mass function for black hole candidates
whereas the first one is observable by a population statistics, e.g. for
Z-sources in low-mass X-ray binaries. The observation of a population gap in
the mass distribution for the latter is suggested as an astrophysical
verification of the existence of a first order phase transition in QCD at high
densities such as the deconfinement.Comment: 4 pages, 2 figures, Contribution to Proceedings of Quark Matter 2002,
Nantes, July 18 - 24, 200
Nuclear structure beyond the neutron drip line: the lowest energy states in He via their T=5/2 isobaric analogs in Li
The level structure of the very neutron rich and unbound He nucleus has
been the subject of significant experimental and theoretical study. Many recent
works have claimed that the two lowest energy He states exist with spins
and and widths on the order of hundreds of keV.
These findings cannot be reconciled with our contemporary understanding of
nuclear structure. The present work is the first high-resolution study with low
statistical uncertainty of the relevant excitation energy range in the
He system, performed via a search for the T=5/2 isobaric analog states
in Li populated through He+p elastic scattering. The present data show
no indication of any narrow structures. Instead, we find evidence for a broad
state in He located approximately 3 MeV above the neutron
decay threshold
Enhanced Production of Neutron-Rich Rare Isotopes in Peripheral Collisions at Fermi Energies
A large enhancement in the production of neutron-rich projectile residues is
observed in the reactions of a 25 MeV/nucleon 86Kr beam with the neutron rich
124Sn and 64Ni targets relative to the predictions of the EPAX parametrization
of high-energy fragmentation, as well as relative to the reaction with the less
neutron-rich 112Sn target. The data demonstrate the significant effect of the
target neutron-to-proton ratio (N/Z) in peripheral collisions at Fermi
energies. A hybrid model based on a deep-inelastic transfer code (DIT) followed
by a statistical de-excitation code appears to account for part of the observed
large cross sections. The DIT simulation indicates that the production of the
neutron-rich nuclides in these reactions is associated with peripheral nucleon
exchange. In such peripheral encounters, the neutron skins of the neutron-rich
124Sn and 64Ni target nuclei may play an important role. From a practical
viewpoint, such reactions between massive neutron-rich nuclei offer a novel and
attractive synthetic avenue to access extremely neutron-rich rare isotopes
towards the neutron-drip line.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
Expanding RIB Capabilities at the Cyclotron Institute: \textsuperscript{3}He-LIG production with an Isobar Separator LSTAR
A new \textsuperscript{3}He-driven IGISOL production station and mass
separator have been designed to produce neutron-deficient low-mass isotopes at
the Cyclotron Institute for the TAMUTRAP facility. The LSTAR design has a mass
resolution to reject contaminants with
efficiency.Comment: Proceeding for EMIS 202
Population clustering as a signal for deconfinement in accreting compact stars
We study the evolution of the rotation frequency for accreting compact stars.
The discontinuous change of the moment of inertia of a rapidly rotating star
due to the possible quark core appearance entails a characteristic change in
the spin evolution. Numerical solutions have been performed using a model
equation of state describing the deconfinement phase transition. Trajectories
of spin evolution are discussed in the angular velocity - baryon number plane
(phase diagram) for different accretion scenarios defined by the initial values
of mass and magnetic field of the star, as well as mass accretion rate and
magnetic field decay time. We observe a characteristic increase in the waiting
time when a configuration enters the quark core regime. Overclustering of the
population of Z sources of LMXBs in the phase diagram is suggested as a direct
measurement of the critical line for the deconfinement phase transition since
it is related to the behaviour of the moment of inertia of the compact star.Comment: 6 pages, 4 figures, uses aastex.cls (included), text and figures
revised, references update
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