5,025 research outputs found
Observations of 20 millisecond pulsars in 47 Tucanae at 20 cm
We have used a new observing system on the Parkes radio telescope to carry
out a series of pulsar observations of the globular cluster 47 Tucanae at 20-cm
wavelength. We detected all 11 previously known pulsars, and have discovered
nine others, all of which are millisecond pulsars in binary systems. We have
searched the data for relatively short orbital period systems, and found one
pulsar with an orbital period of 96 min, the shortest of any known radio
pulsar.
The increased rate of detections with the new system resulted in improved
estimates of the flux density of the previously known pulsars, determination of
the orbital parameters of one of them, and a coherent timing solution for
another one. Five of the pulsars now known in 47 Tucanae have orbital periods
of a few hours and implied companion masses of only ~ 0.03 Msun. Two of these
are eclipsed at some orbital phases, while three are seen at all phases at 20
cm but not always at lower frequencies. Four and possibly six of the other
binary systems have longer orbital periods and companion masses ~ 0.2 Msun,
with at least two of them having relatively large orbital eccentricities. All
20 pulsars have rotation periods in the range 2-8 ms.Comment: 15 pages, 6 embedded EPS figures, to be published in The
Astrophysical Journa
Mean curvature flow with triple junctions in higher space dimensions
We consider mean curvature flow of n-dimensional surface clusters. At
(n-1)-dimensional triple junctions an angle condition is required which in the
symmetric case reduces to the well-known 120 degree angle condition. Using a
novel parametrization of evolving surface clusters and a new existence and
regularity approach for parabolic equations on surface clusters we show local
well-posedness by a contraction argument in parabolic Hoelder spaces.Comment: 31 pages, 2 figure
Semiclassical dynamics of domain walls in the one-dimensional Ising ferromagnet in a transverse field
We investigate analytically and numerically the dynamics of domain walls in a
spin chain with ferromagnetic Ising interaction and subject to an external
magnetic field perpendicular to the easy magnetization axis (transverse field
Ising model). The analytical results obtained within the continuum
approximation and numerical simulations performed for discrete classical model
are used to analyze the quantum properties of domain walls using the
semiclassical approximation. We show that the domain wall spectrum shows a band
structure consisting of 2 non-intersecting zones.Comment: 15 pages, 9 figure
Deppining of a Superfluid Vortex Inside a Circular Defect
In this work we study the process of depinning of a quantum of circulation
trapped inside a disk by an applied two dimensional superflow. We use the
Gross-Pitaevskii model to describe the neutral superfluid. The collective
coordinate dynamics is derived directly from the condensate equation of motion,
the nonlinear Schroedinger equation, and it is used to obtain an expression for
the critical velocity as a function of the defect radius. This expression is
compared with a numerical result obtained from the time independent nonlinear
Schroedinger equation. Below the critical velocity, we obtain the dependence of
the semiclassical nucleation rate with the flow velocity at infinity. Above the
critical velocity, the classical vortex depinning is illustrated with a
numerical simulation of the time dependent nonlinear Schroedinger equation.Comment: 8 pages, 5 figures, uses revtex and epsf.st
PSR J1723-2837: An Eclipsing Binary Radio Millisecond Pulsar
We present a study of PSR J1723-2837, an eclipsing, 1.86 ms millisecond
binary radio pulsar discovered in the Parkes Multibeam survey. Radio timing
indicates that the pulsar has a circular orbit with a 15 hr orbital period, a
low-mass companion, and a measurable orbital period derivative. The eclipse
fraction of ~15% during the pulsar's orbit is twice the Roche lobe size
inferred for the companion. The timing behavior is significantly affected by
unmodeled systematics of astrophysical origin, and higher-order orbital period
derivatives are needed in the timing solution to account for these variations.
We have identified the pulsar's (non-degenerate) companion using archival
ultraviolet, optical, and infrared survey data and new optical photometry.
Doppler shifts from optical spectroscopy confirm the star's association with
the pulsar and indicate a pulsar-to-companion mass ratio of 3.3 +/- 0.5,
corresponding to a companion mass range of 0.4 to 0.7 Msun and an orbital
inclination angle range of between 30 and 41 degrees, assuming a pulsar mass
range of 1.4-2.0 Msun. Spectroscopy indicates a spectral type of G for the
companion and an inferred Roche-lobe-filling distance that is consistent with
the distance estimated from radio dispersion. The features of PSR J1723-2837
indicate that it is likely a "redback" system. Unlike the five other Galactic
redbacks discovered to date, PSR J1723-2837 has not been detected as a
gamma-ray source with Fermi. This may be due to an intrinsic spin-down
luminosity that is much smaller than the measured value if the unmeasured
contribution from proper motion is large.Comment: 11 pages, including 8 figures and 5 tables. Accepted by the
Astrophysical Journa
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