144 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
Computing Bi-Lipschitz Outlier Embeddings into the Line
The problem of computing a bi-Lipschitz embedding of a graphical metric into
the line with minimum distortion has received a lot of attention. The
best-known approximation algorithm computes an embedding with distortion
, where denotes the optimal distortion [B\u{a}doiu \etal~2005]. We
present a bi-criteria approximation algorithm that extends the above results to
the setting of \emph{outliers}.
Specifically, we say that a metric space admits a
-embedding if there exists , with , such that
admits an embedding into the line with distortion at
most . Given , and a metric space that admits a -embedding,
for some , our algorithm computes a -embedding in polynomial time. This is the first algorithmic result for
outlier bi-Lipschitz embeddings. Prior to our work, comparable outlier
embeddings where known only for the case of additive distortion
An Algorithm for the Simulations of the Magnetized Neutron Star Cooling
The model and algorithm for the cooling of the magnetized neutron stars are
presented. The cooling evolution described by system of parabolic partial
differential equations with non-linear coefficients is solved using Alternating
Direction Implicit method. The difference scheme and the preliminary results of
simulations are presented.Comment: 6 pages, 4 figures, accepted to the European Physical Journal Web of
Conferences as a contribution of the International Conference Mathematical
Modeling and Computational Physics 2015 (High Tatra Mountains, Slovakia, July
13 - July 17, 2015, http://web.tuke.sk/mmcp/mmcp2015/
Cooling of Hybrid Stars with Spin Down Compression
We study the cooling of hybrid stars coupling with spin-down. Due to the
spin-down of hybrid stars, the interior density continuously increases,
different neutrino reactions may be triggered(from the modified Urca process to
the quark and nucleon direct Urca process) at different stages of evolution. We
calculate the rate of neutrino emissivity of different reactions and simulate
the cooling curves of the rotational hybrid stars. The results show the cooling
curves of hybrid stars clearly depend on magnetic field if the direct urca
reactions occur during the spin-down. Comparing the results of the rotational
star model with the transitional static model, we find the cooling behavior of
rotational model is more complicated, the temperature of star is higher,
especially when direct urca reactions appear in process of rotation. And then
we find that the predicted temperatures of some rotating hybrid stars are
compatible with the pulsar's data which are contradiction with the results of
transitional method.Comment: 8 pages, 5figures, accepted by RA
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
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
Spin-down of Relativistic Stars with Phase Transitions and PSR J0537-6910
Using a highly accurate numerical code, we study the spin down of rotating
relativistic stars, undergoing a quark deconfinement phase transition. Such
phase transitions have been suggested to yield an observable signal in the
braking index of spinning-down pulsars, which is based on a ``backbending''
behaviour of the moment of inertia. We focus on a particular equation of state
that has been used before to study this behaviour, and find that for the
population of normal pulsars the moment of inertia does not exhibit a
backbending behaviour. In contrast, for supramassive millisecond pulsars a very
strong backbending behaviour is found. Essentially, once a quark core appears
in a spinning-down supramassive millisecond pulsar, the star spins up and
continues to do so until it reaches the instability to collapse. This strong
spin-up behaviour makes it easier to distinguish a phase transition in such
pulsars: a negative first time-derivative of the rotational period suffices and
one does not have to measure the braking index. In the spin-up era, the usually
adopted spin-down power law fails to describe the evolution of the angular
velocity. We adopt a general-relativistic spin-down power law and derive the
equations that describe the angular velocity and braking index evolution in
rapidly rotating pulsars.Comment: 10 pages, 10 figures, additional results and conclusions, matches
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