5,945 research outputs found
X-Ray Observations of Black Widow Pulsars
We describe the first X-ray observations of five short orbital period ( day), -ray emitting, binary millisecond pulsars. Four of these, PSRs
J0023+0923, J11243653, J1810+1744, and J22561024 are `black-widow'
pulsars, with degenerate companions of mass , three of which
exhibit radio eclipses. The fifth source, PSR J2215+5135, is an eclipsing
`redback' with a near Roche-lobe filling 0.2 solar mass non-degenerate
companion. Data were taken using the \textit{Chandra X-Ray Observatory} and
covered a full binary orbit for each pulsar. Two pulsars, PSRs J2215+5135 and
J22561024, show significant orbital variability while PSR J11243653 shows
marginal orbital variability. The lightcurves for these three pulsars have
X-ray flux minima coinciding with the phases of the radio eclipses. This
phenomenon is consistent with an intrabinary shock emission interpretation for
the X-rays. The other two pulsars, PSRs J0023+0923 and J1810+1744, are fainter
and do not demonstrate variability at a level we can detect in these data. All
five spectra are fit with three separate models: a power-law model, a blackbody
model, and a combined model with both power-law and blackbody components. The
preferred spectral fits yield power-law indices that range from 1.3 to 3.2 and
blackbody temperatures in the hundreds of eV. The spectrum for PSR J2215+5135
shows a significant hard X-ray component, with a large number of counts above 2
keV, which is additional evidence for the presence of intrabinary shock
emission and is similar to what has been detected in the low-mass X-ray binary
to millisecond pulsar transition object PSR J1023+0038.Comment: 8 pages, 6 figures, 2 tables, submitted to Ap
Gaussian coordinate systems for the Kerr metric
We present the whole class of Gaussian coordinate systems for the Kerr
metric. This is achieved through the uses of the relationship between Gaussian
observers and the relativistic Hamilton-Jacobi equation. We analyze the
completeness of this coordinate system. In the appendix we present the
equivalent JEK formulation of General Relativity -- the so-called
quasi-Maxwellian equations -- which acquires a simpler form in the Gaussian
coordinate system. We show how this set of equations can be used to obtain the
internal metric of the Schwazschild solution, as a simple example. We suggest
that this path can be followed to the search of the internal Kerr metric
Analysis of cancellation in two-dimensional magnetohydrodynamic turbulence
A signed measure analysis of two-dimensional intermittent magnetohydrodynamic
turbulence is presented. This kind of analysis is performed to characterize the
scaling behavior of the sign-oscillating flow structures, and their geometrical
properties. In particular, it is observed that cancellations between positive
and negative contributions of the field inside structures, are inhibited for
scales smaller than the Taylor microscale, and stop near the dissipative scale.
Moreover, from a simple geometrical argument, the relationship between the
cancellation exponent and the typical fractal dimension of the structures in
the flow is obtained.Comment: 21 pages, 5 figures (3 .jpg not included in the latex file
Characterization of InGaN/GaN multi-quantum-well blue-light-emitting diodes grown by metal organic chemical vapor deposition
The structural,surface morphology, and the temperature dependence photoluminescence of InGaN(3 nm)/GaN(7 nm) 5 period multi-quantum-well blue-light-emitting diode (LED)structures grown by metal organic chemical vapor deposition(MOCVD) have been studied. Quantum dot-likestructures and strain contrast evident by black lumps were observed in the quantum wells using high-resolution transmission electron microscopy(HRTEM) analysis. Double-crystal high-resolution x-ray diffraction (HRXRD) spectra of blue LED were simulated using kinematical theory method, to obtain composition, and period thickness of well and barrier. The âSâ shape character shift as redâblueâredshift of the quantum-well emission line, i.e., blue emission peak 2.667 eV at 10 K, was observed with variation of temperature in the photoluminescence (PL) spectra. The shift is assigned to the potential fluctuations due to alloy inhomogeneous distribution in the quantum wells. The In composition in the quantum wells obtained by two independent techniques, namely HRXRD and PL, was 8% and 19%, respectively. The reason for this large difference in composition is explained in this letter
Quantum Breathers in a Nonlinear Lattice
We study nonlinear phonon excitations in a one-dimensional quantum nonlinear
lattice model using numerical exact diagonalization. We find that multi-phonon
bound states exist as eigenstates which are natural counterparts of breather
solutions of classical nonlinear systems. In a translationally invariant
system, these quantum breather states form particle-like bands and are
characterized by a finite correlation length. The dynamic structure factor has
significant intensity for the breather states, with a corresponding quenching
of the neighboring bands of multi-phonon extended states.Comment: 4 pages, RevTex, 4 postscript figures, Physical Relview Letters (in
press
The orbital poles of Milky Way satellite galaxies: a rotationally supported disc-of-satellites
Available proper motion measurements of Milky Way (MW) satellite galaxies are
used to calculate their orbital poles and projected uncertainties. These are
compared to a set of recent cold dark-matter (CDM) simulations, tailored
specifically to solve the MW satellite problem. We show that the CDM satellite
orbital poles are fully consistent with being drawn from a random distribution,
while the MW satellite orbital poles indicate that the disc-of-satellites of
the Milky Way is rotationally supported. Furthermore, the bootstrapping
analysis of the spatial distribution of theoretical CDM satellites also shows
that they are consistent with being randomly drawn. The theoretical CDM
satellite population thus shows a significantly different orbital and spatial
distribution than the MW satellites, most probably indicating that the majority
of the latter are of tidal origin rather than being DM dominated
sub-structures. A statistic is presented that can be used to test a possible
correlation of satellite galaxy orbits with their spatial distribution.Comment: Accepted for publication in Ap
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