1,715 research outputs found
INTEGRAL observations of V0332+53 in outburst
We present the analysis of a 100ksec Integral(3-100kev) observation of the
transient X-ray pulsar V0332+53 inoutburst. The source is pulsating at
P=4.3751+/-0.0002s with a clear double pulse from 6 kev to 60 kev. The average
flux was ~550mCrab between 20 kev and 60 kev. We modeled the broad band
continuum from 5 kev to 100 kev with a power-law modified by an exponential cut
off. We observe three cyclotron lines: the fundamental line at 24.9+/-0.1 kev,
the first harmonic at 50.5+/-0.1 kev as well as the second harmonic
at71.7+/-0.8 kev, thus confirming the discovery of the harmonic lines by Coburn
et al. (2005) in RXTE data.Comment: 4 pages, 3 figures. Accepted for publication in A&A Letter
Discovery of new quasi-periodic oscillations in the X-ray transient source V~0332+53
We report the discovery of a new quasi-period oscillation (QPO) at 0.22 Hz,
centered on the source spin frequency of the high mass X-ray binary system
V~0332+53 when the source was observed during its November 2004/March 2005
outburst by {\em RXTE}. Besides this new QPO, we also detected the known 0.05
Hz QPO. Both the 0.22 and 0.05 Hz QPOs stand out clearly at a mid-flux level of
the outburst within January 15--19 2005, and later at an even lower flux level
as the width of 0.22 Hz QPO drops. No evolution of the centroid frequency with
the flux is seen in either QPO. The rms value below 10 keV is around 4--6% for
both QPOs and decreases at higher energies. We discuss our results in the
context of current QPO models.Comment: 5 figures, 12 pages. AASTex preprint style. (In 2005, ApJ Let., 629,
L33
Contact inhibition of locomotion and mechanical cross-talk between cell-cell and cell-substrate adhesion determines the pattern of junctional tension in epithelial cell aggregates
We generated a computational approach to analyze the biomechanics of
epithelial cell aggregates, either island or stripes or entire monolayers, that
combines both vertex and contact-inhibition-of-locomotion models to include
both cell-cell and cell-substrate adhesion. Examination of the distribution of
cell protrusions (adhesion to the substrate) in the model predicted high order
profiles of cell organization that agree with those previously seen
experimentally. Cells acquired an asymmetric distribution of basal protrusions,
traction forces and apical aspect ratios that decreased when moving from the
edge to the island center. Our in silico analysis also showed that tension on
cell-cell junctions and apical stress is not homogeneous across the island.
Instead, these parameters are higher at the island center and scales up with
island size, which we confirmed experimentally using laser ablation assays and
immunofluorescence. Without formally being a 3-dimensional model, our approach
has the minimal elements necessary to reproduce the distribution of cellular
forces and mechanical crosstalk as well as distribution of principal stress in
cells within epithelial cell aggregates. By making experimental testable
predictions, our approach would benefit the mechanical analysis of epithelial
tissues, especially when local changes in cell-cell and/or cell-substrate
adhesion drive collective cell behavior.Comment: 39 pages, 8 Figures. Supplementary Information is include
Diffuse Galactic Soft Gamma-Ray Emission
The Galactic diffuse soft gamma-ray (30-800 keV) emission has been measured
from the Galactic Center by the HIREGS balloon-borne germanium spectrometer to
determine the spectral characteristics and origin of the emission. The
resulting Galactic diffuse continuum is found to agree well with a single
power-law (plus positronium) over the entire energy range, consistent with RXTE
and COMPTEL/CGRO observations at lower and higher energies, respectively. We
find no evidence of spectral steepening below 200 keV, as has been reported in
previous observations. The spatial distribution along the Galactic ridge is
found to be nearly flat, with upper limits set on the longitudinal gradient,
and with no evidence of an edge in the observed region. The soft gamma-ray
diffuse spectrum is well modeled by inverse Compton scattering of interstellar
radiation off of cosmic-ray electrons, minimizing the need to invoke
inefficient nonthermal bremsstrahlung emission. The resulting power requirement
is well within that provided by Galactic supernovae. We speculate that the
measured spectrum provides the first direct constraints on the cosmic-ray
electron spectrum below 300 MeV.Comment: 26 pages, 7 figure, submitted to Ap
INTEGRAL observation of the high-mass X-ray transient V 0332+53 during the 2005 outburst decline
The decline of the high mass X-ray transient V 0332+53 during the Dec. 2004 to Feb. 2005 outburst is analysed from the data recorded by INTEGRAL. The flux is shown to decrease exponentially until 2005 Feb. 10, with a decay time scale of âŒ30 days above 20 keV and âŒ20 days at lower energies, and to decrease linearly thereafter.
The energy spectrum is well modelled throughout the decay by a power law with a folding energy of âŒ7.5 keV, and with two cyclotron absorption features. The folding energy does not vary significantly over the decay, but the spectrum becomes harder with time. Most importantly, we show that the parameters describing the fundamental cyclotron line around 27 keV do vary with time: its energy and depth increase (by about 17% for the energy in âŒ6 weeks), while its width decreases. These changes of the cyclotron line parameters are interpreted as resulting from a change in the extent of the cyclotron scattering region.
Two quasi-periodic oscillations are also observed at various times during the observations, one at 0.05 Hz and another one near the pulsation frequency around 0.23 Hz
Optical Activity From Extra Dimension
Optical activity, like Faraday effect, is a rotation of the plane of
polarization of propagating light in a medium and can be attributed to
different sources with distinct signatures. In this note we discuss the effect
of optical activity {\it{in vacuum}} due to Kaluza-Klein scalar field ,
in the presence of an external electro-magnetic field. The astrophysical
implication of this effect is indicated. We also point out the possibility of
observing the same in laboratory conditions.Comment: Four Page
Implications of the -ray Polarization of GRB 021206
We compare two possible scenarios for the producing of high level of
polarization within the prompt emission of a GRB: synchrotron emission from a
relativistic jet with a uniform (in space and time) magnetic field and
synchrotron emission from a jet with a random magnetic field in the plane of
the shock. Somewhat surprisingly we find that both scenarios can produce a
comparable level of polarization (% for the uniform field and % for a random field). Uniform time independent field most naturally
arises by expansion of the field from the compact object. It requires a
G field at the source and a transport of the field as . It {\it does not} imply Poynting flux domination of the energy of the
wind. There is a serious difficulty however, within this scenario, accounting
for particle acceleration (which requires random magnetic fields) both for
Poynting flux and non-Poynting flux domination. Significant polarization can
also arise from a random field provided that the observer is located within
orientation from a narrow () jet. While most
jets are wider, the jet of GRB 021206 from which strong polarization was
recently observed, was most likely very narrow. GRB 021206 is among the
strongest bursts ever. Adopting the energy-angle relation we find an estimated
angle of rad or even smaller. Thus, for this particular burst the
required geometry is not unusual. We conclude that the RHESSI observations
suggest that the prompt emission results from synchrotron radiation. However,
in view of the comparable levels of polarizations predicted by both the random
field and the homogeneous field scenarios these observations are insufficient
to rule out or confirm either one.Comment: 14 pages, 4 figure
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