29,744 research outputs found
Multiwavelength Observations of GX 339-4 in 1996. II. Rapid X-ray Variability
As part of our multiwavelength campaign of GX 339-4 observations in 1996 we
present the rapid X-ray variability observed July 26 using the RXTE when the
source was in a hard state (= soft X-ray low state). We found that the source
was extremely variable, with many bright flares. The flares have relatively
symmetric time profiles. There are a few time intervals where the flux rises
steadily and then drops suddenly, sometimes to a level lower than the average
before the increase. Hardness ratios showed that the source was slightly softer
when the flux was brighter. The power density spectra (PDS) were also
complicated and we found that broken power laws do not provide adequate fits to
any of them. Instead a pair of zero-centered Lorentzians gives a good general
description of the shape of the PDS. We found several quasi-periodic
oscillations (QPO), including some that are harmonically spaced with the most
stable frequency at 0.35 Hz. While the overall rms variability of the source
was close to being constant throughout the observation (29% integrating between
0.01 and 50 Hz), there is a small but significant change in the PDS shape with
time. More importantly, we show that the soft 2-5 keV band is more variable
than the harder 5-10 and 10-40 keV bands, which is unusual for this source and
for other black hole candidates. Cross correlation functions (CCF) between
these bands show that the light curve for the 10-40 keV band lags that of the
2-5 keV band by 5 msec.Comment: Submitted to Astrophysical Journal. 20 pages. 8 figure
No Evidence for Orbital Loop Currents in Charge Ordered YBaCuO from Polarized Neutron Diffraction
It has been proposed that the pseudogap state of underdoped cuprate
superconductors may be due to a transition to a phase which has circulating
currents within each unit cell. Here, we use polarized neutron diffraction to
search for the corresponding orbital moments in two samples of underdoped
YBaCuO with doping levels and 0.123. In contrast to
some other reports using polarized neutrons, but in agreement with nuclear
magnetic resonance and muon spin rotation measurements, we find no evidence for
the appearance of magnetic order below 300 K. Thus, our experiment suggests
that such order is not an intrinsic property of high-quality cuprate
superconductor single crystals. Our results provide an upper bound for a
possible orbital loop moment which depends on the pattern of currents within
the unit cell. For example, for the CC- pattern proposed by Varma,
we find that the ordered moment per current loop is less than 0.013 for
.Comment: Comments in arXiv:1710.08173v1 fully addresse
Analyses of the Konus catalogue of gamma-ray bursts with the thermal synchrotron model
Approximately 150 reported gamma bursts of the Konus catalogue using the thermal synchrotron model are analyzed. An overwhelming majority of these spectra can be satsifactorily fitted by theoretical thermal synchrotron spectra of mildly relativistic electrons in strong magnetic fields, making the strong-field neutron star picture at least self-consistent. Valuable additional information is also extracted from various spectral features contained in many of the events
A Peculiar Flaring Episode of Cygnus X-1
Recent monitoring of Cyg X-1 with {\em RXTE} revealed a period of intense
flaring, which started in October of 2000 and lasted until March of 2001. The
source exhibited some quite unusual behaviors during this period. The soft
X-ray flux of the source went up and down three times on a timescale of about
one month, as discovered by the ASM aboard RXTE, before finally returning to
the normal level (of the hard state). The observed spectral and temporal X-ray
properties of Cyg X-1 are mostly intermediate between the canonical hard and
soft states. This is known previously for strong X-ray flares, however, we show
that the source did enter a period that resembles, in many ways, a sustained
soft state during the last of the three flares. We make detailed comparisons
between this flare and the 1996 state transition, in terms of the observed
X-ray properties, such as flux--hardness correlation, X-ray spectrum, and power
density spectrum. We point out the similarities and differences, and discuss
possible implications of the results on our understanding of the phenomena of
flares and state transitions associated with Cyg X-1.Comment: 4 pages, 3 figures, accepted for publication in ApJ Letter
Semiclassical Analysis of the Wigner Symbol with One Small Angular Momentum
We derive an asymptotic formula for the Wigner symbol, in the limit of
one small and 11 large angular momenta. There are two kinds of asymptotic
formulas for the symbol with one small angular momentum. We present the
first kind of formula in this paper. Our derivation relies on the techniques
developed in the semiclassical analysis of the Wigner symbol [L. Yu and R.
G. Littlejohn, Phys. Rev. A 83, 052114 (2011)], where we used a gauge-invariant
form of the multicomponent WKB wave-functions to derive asymptotic formulas for
the symbol with small and large angular momenta. When applying the same
technique to the symbol in this paper, we find that the spinor is
diagonalized in the direction of an intermediate angular momentum. In addition,
we find that the geometry of the derived asymptotic formula for the
symbol is expressed in terms of the vector diagram for a symbol. This
illustrates a general geometric connection between asymptotic limits of the
various symbols. This work contributes the first known asymptotic formula
for the symbol to the quantum theory of angular momentum, and serves as a
basis for finding asymptotic formulas for the Wigner symbol with two
small angular momenta.Comment: 15 pages, 14 figure
Optimum spectral window for imaging of art with optical coherence tomography
Optical Coherence Tomography (OCT) has been shown to have potential for important applications in the field of art conservation and archaeology due to its ability to image subsurface microstructures non-invasively. However, its depth of penetration in painted objects is limited due to the strong scattering properties of artists’ paints. VIS-NIR (400 nm – 2400 nm) reflectance spectra of a wide variety of paints made with historic artists’ pigments have been measured. The best spectral window with which to use optical coherence tomography (OCT) for the imaging of subsurface structure of paintings was found to be around 2.2 μm. The same spectral window would also be most suitable for direct infrared imaging of preparatory sketches under the paint layers. The reflectance spectra from a large sample of chemically verified pigments provide information on the spectral transparency of historic artists’ pigments/paints as well as a reference set of spectra for pigment identification. The results of the paper suggest that broadband sources at ~2 microns are highly desirable for OCT applications in art and potentially material science in general
Glueballs and Instantons
We study correlation functions and Bethe Salpeter amplitudes for the scalar,
the pseudoscalar and the tensor glueballs using an instanton-based model of the
QCD vacuum. We consider both the pure gauge case and the situation for real QCD
with two light quark flavors. We show that instantons lead to a strong
modification of the correlation functions as compared to their perturbative
behavior. In particular, we find a strong attractive force in the
channel and repulsion in the channel. Due to the
strong classical field of the instantons, these effects are much larger than
the spin splittings observed in mesons made of quarks. The resulting masses,
coupling constants and wave functions appear to be in agreement with lattice
gauge simulations.Comment: revised version published in Phys. Rev. Let
Two-dimensional gapless spin liquids in frustrated SU(N) quantum magnets
A class of the symmetrically frustrated SU(N) models is constructed for
quantum magnets based on the generators of SU(N) group. The total Hamiltonian
lacks SU(N) symmtry. A mean field theory in the quasi-particle representation
is developed for spin liquid states. Numerical solutions in two dimension
indicate that the ground states are gapless and the quasi-particles are Dirac
particles. The mechanism may be helpful in exploring the spin liquid phases in
the spin-1 bilinear-biquadratic model and the spin-orbital model in higher
dimensions.Comment: 9 pages, 3 figures, to appear in New Journal of Physic
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