506 research outputs found
On the evolution of the radio pulsar PSR J1734−3333
Recent measurements showed that the period derivative of the ‘hig
h-B’ radio pulsar PSR J1734−3333 is increasing with time. For neutron stars evolving with fallback disks, this rotational behavior is expected in certain phases of the long-term evolution. Using the same model as employed earlier to explain the evolution of anomalous X-ray pulsars and soft gamma-ray repeaters, we show that the period,the first and second period derivatives and the X-ray luminosity of this source can simultaneously acquire the observed values for a neutron star evolving with a fallback disk. We find that the required strength of the dipole field that can produce the source properties is in the range of 10^12 − 10^13 G on the pole of the neutron star. When the model source
reaches the current state properties of PSR J1734−3333, accretion onto the star has not started yet, allowing the source to operate as a regular radio pulsar. Our results imply that PSR J1734−3333 is at an age of ∼3×10^4 −2×10^5years. Such sources will have properties like the X-ray dim isolated neutron stars or transient AXPs at a later epoch of weak accretion from the diminished fallback disk
Neutron Star Superfluidity, Dynamics and Precession
Basic rotational and magnetic properties of neutron superfluids and proton
superconductors in neutron stars are reviewed. The modes of precession of the
neutron superfluid are discussed in detail. We emphasize that at finite
temperature, pinning of superfluid vortices does not offer any constraint on
the precession. Any pinning energies can be surmounted by thermal activation
and there exists a dynamical steady state in which the superfluid follows the
precession of the crust at a small lag angle between the crust and superfluid
rotation velocity vectors. At this small lag the system is far from the
critical conditions for unpinning, even if the observed precession of the crust
may entail a large angle between the figure axis and the crust's rotation
velocity vector. We conclude that if long period modulations of pulse arrival
times and pulse shapes observed in a pulsar like the PSR B1828-11 are due to
the precession of the neutron star, this does not have any binding implications
about the existence of pinning by flux lines or the existence of Type II
superconductivity in the neutron star.Comment: 21 pages, one figure, to appear in the Proceedings of the NATO-ASI
"The Electromagnetic Spectrum of Neutron Stars" held in Marmaris, Turkey,
June 2004, eds. A. Baykal, S.K. Yerli, C. Inam and S. Grebene
Linking the X-ray timing and spectral properties of the glitching AXP 1RXS J170849-400910
Previous studies of the X-ray flux and spectral properties of 1RXS
J170849-400910 showed hints of a possible correlation with the spin glitches
that occurred in 1999 and 2001. However, due to the sparseness of spectral
measurements and the paucity of detected glitches no firm conclusion could be
drawn. We retrieved and analysed archival XTE pointings of 1RXS J170849-400910
covering the time interval between January 2003 and June 2006 and carried out a
detailed timing analysis by means of phase fitting techniques. We detected two
relatively large glitches Delta nu / nu of 1.2 and 2.1 10^-6 occurred in
January and June 2005. Interestingly, the occurrence times of these glitches
are in agreement with the predictions made in our previous studies. This
finding strongly suggests a connection between the flux, spectral and timing
properties of 1RXS J170849-400910.Comment: Submitted to A&A, 4 pages; results presented at the INT meeting "The
Neutron Star Crust and Surface: Observations and Models" on June 27; referee
comments adde
ROSAT Observations of the Vela Pulsar
The ROSAT HRI was used to monitor X-ray emission from the Vela Pulsar. Six
observations span 2-1/2 years and 3 glitches. The summed data yield a
determination of the pulse shape, and X-ray emission from the pulsar is found
to be 12 % pulsed with one broad and two narrow peaks. One observation occurred
15 days after a large glitch. No change in pulse structure was observed and any
change in X-ray luminosity, if present, was less than 3 %. Implications for
neutron star structure are discussed.Comment: To be publisned in the Astrophysical Journa
The rigidity of crystalline color superconducting quark matter
We calculate the shear modulus of crystalline color superconducting quark
matter, showing that this phase of dense, but not asymptotically dense,
three-flavor quark matter responds to shear stress like a very rigid solid. To
evaluate the shear modulus, we derive the low energy effective Lagrangian that
describes the phonons that originate from the spontaneous breaking of
translation invariance by the spatial modulation of the gap parameter .
These massless bosons describe space- and time-dependent fluctuations of the
crystal structure and are analogous to the phonons in ordinary crystals. The
coefficients of the spatial derivative terms of the phonon effective Lagrangian
are related to the elastic moduli of the crystal; the coefficients that encode
the linear response of the crystal to a shearing stress define the shear
modulus. We analyze the two particular crystal structures which are
energetically favored over a wide range of densities, in each case evaluating
the phonon effective action and the shear modulus up to order in a
Ginzburg-Landau expansion, finding shear moduli which are 20 to 1000 times
larger than those of neutron star crusts. The crystalline color superconducting
phase has long been known to be a superfluid -- by picking a phase its order
parameter breaks the quark-number symmetry spontaneously. Our results
demonstrate that this superfluid phase of matter is at the same time a rigid
solid. We close with a rough estimate of the pinning force on the rotational
vortices which would be formed embedded within this rigid superfluid upon
rotation. Our results raise the possibility that (some) pulsar glitches could
originate within a quark matter core deep within a neutron star.Comment: 38 pages, 5 figures. v3. Two new paragraphs in Section V
(Conclusion); some additional small changes. A paragraph discussing
supercurrents added in Section I (Introduction). Version to appear in Phys.
Rev.
The effect of the neutron star crust on the evolution of a core magnetic field
We consider the expulsion of the magnetic field from the super-conducting
core of a neutron star and its subsequent decay in the crust. Particular
attention is paid to a strong feedback of the distortion of magnetic field
lines in the crust on the expulsion of the flux from the core. This causes a
considerable delay of the core flux expulsion if the initial field strength is
larger than 10^{11} G. It is shown that the hypothesis on the magnetic field
expulsion induced by the neutron star spin-down is adequate only for a
relatively weak initial magnetic field G. The expulsion
time-scale depends not only on the conductivity of the crust, but also on the
initial magnetic field strength itself. Our model of the field evolution
naturally explains the existence of the residual magnetic field of neutron
stars. Its strength is correlated with the impurity concentration in neutron
star crusts and anti-correlated with the initial field strengths.Comment: 15 pages, 6 figures, accepted to MNRA
Transcutaneous immunisation assisted by low-frequency ultrasound.
Low-frequency ultrasound application is known to increase the skin's permeability to large molecules such as vaccines, and to enable transcutaneous immunisation. Sodium dodecyl sulphate (SDS) - a skin irritant - is often included in the coupling medium at 1% (w/v), as this has been found to enhance skin permeability. In this paper we show, for the first time, the feasibility of low-frequency ultrasound-assisted transcutaneous immunisation in the absence of SDS. Antibody titres were strongly influenced by experimental conditions. SDS presence in the coupling medium increased antibody titres, though a lower concentration of 0.5% (w/v) generated much higher titres than the commonly used 1% (w/v), despite causing less skin damage. A lower ultrasound duty cycle of 10% generated higher antibody titres than a duty cycle of 20%, also despite causing lower skin damage. Such lack of correlation between skin damage and immune responses indicates that enhancement of skin permeability to topically applied antigen (as indicated by changes in skin integrity) was not the main mechanism of low-frequency ultrasound-assisted skin immunisation
Crystalline Color Superconductivity
In any context in which color superconductivity arises in nature, it is
likely to involve pairing between species of quarks with differing chemical
potentials. For suitable values of the differences between chemical potentials,
Cooper pairs with nonzero total momentum are favored, as was first realized by
Larkin, Ovchinnikov, Fulde and Ferrell (LOFF). Condensates of this sort
spontaneously break translational and rotational invariance, leading to gaps
which vary periodically in a crystalline pattern. Unlike the original LOFF
state, these crystalline quark matter condensates include both spin zero and
spin one Cooper pairs. We explore the range of parameters for which crystalline
color superconductivity arises in the QCD phase diagram. If in some shell
within the quark matter core of a neutron star (or within a strange quark star)
the quark number densities are such that crystalline color superconductivity
arises, rotational vortices may be pinned in this shell, making it a locus for
glitch phenomena.Comment: 40 pages, LaTeX with eps figs. v2: New paragraph on Ginzburg-Landau
treatment of LOFF phase in section 5. References added. v3: Small changes
only. Version to appear in Phys. Rev.
Time-Correlated Structure in Spin Fluctuations in Pulsars
We study statistical properties of stochastic variations in pulse arrival
times, timing noise, in radio pulsars using a new analysis method applied in
the time domain. The method proceeds in two steps. First, we subtract
low-frequency wander using a high-pass filter. Second, we calculate the
discrete correlation function of the filtered data. As a complementary method
for measuring correlations, we introduce a statistic that measures the
dispersion of the data with respect to the data translated in time. The
analysis methods presented here are robust and of general usefulness for
studying arrival time variations over timescales approaching the average
sampling interval. We apply these methods to timing data for 32 pulsars. In two
radio pulsars, PSRs B1133+16 and B1933+16, we find that fluctuations in arrival
times are correlated over timescales of 10 - 20 d with the distinct signature
of a relaxation process. Though this relaxation response could be
magnetospheric in origin, we argue that damping between the neutron star crust
and interior liquid is a more likely explanation. Under this interpretation,
our results provide the first evidence independent from pulsar spin glitches of
differential rotation in neutron stars. PSR B0950+08, shows evidence for
quasi-periodic oscillations that could be related to mode switching.Comment: 25 pages, Final journal version (MNRAS
X-ray enhancement and long-term evolution of swift J1822.3-1606
We investigate the X-ray enhancement and the long-term evolution of the recently discovered second "low-B magnetar" Swift J1822.3-1606 in the frame of the fallback disk model. During a soft gamma burst episode, the inner disk matter is pushed back to larger radii, forming a density gradient at the inner disk. Subsequent relaxation of the inner disk could account for the observed X-ray enhancement light curve of Swift J1822.3-1606. We obtain model fits to the X-ray data with basic disk parameters similar to those employed to explain the X-ray outburst light curves of other anomalous X-ray pulsars and soft gamma repeaters. The long period (8.4 s) of the neutron star can be reached by the effect of the disk torques in the long-term accretion phase ((1-3) x 10(5) yr). The currently ongoing X-ray enhancement could be due to a transient accretion epoch, or the source could still be in the accretion phase in quiescence. Considering these different possibilities, we determine the model curves that could represent the long-term rotational and the X-ray luminosity evolution of Swift J1822.3-1606, which constrain the strength of the magnetic dipole field to the range of (1-2) x 10(12) G on the surface of the neutron star
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