1,459 research outputs found
Analysis of intermittency in submillimeter radio and hard x-ray data during the impulsive phase of a solar flare
We present an analysis of intermittent processes occurring during the impulsive phase of the flare SOL2012-03-13, using hard X-rays and submillimeter radio data. Intermittency is a key characteristic in turbulent plasmas and has so far only been analyzed for hard X-ray data. Since in a typical flare the same accelerated electron population is believed to produce both hard X-rays and gyrosynchrotron radiation, we compare the two time profiles by searching for intermittency signatures. For this, we define a cross-wavelet power spectrum, which is used to obtain the local intermittency measure, or LIMLIM. When greater than three, the square LIMLIM coefficients indicate a local intermittent process. The LIM2LIM2 coefficient distribution in time and scale helps to identify avalanche or cascade energy release processes. We find two different and well-separated intermittent behaviors in the submillimeter data: for scales greater than 20 s, a broad distribution during the rising and maximum phases of the emission seems to favor a cascade process; for scales below 1 s, short pulses centered on the peak time are representative of avalanches. When applying the same analysis to hard X-rays, we find that only the scales above 10 s produce a distribution related to a cascade energy fragmentation. Our results suggest that different acceleration mechanisms are responsible for tens of keV and MeV energy ranges of electrons
Orbital phase resolved spectroscopy of 4U1538-52 with MAXI
4U 1538-52, an absorbed high mass X-ray binary with an orbital period of 3.73
days, shows moderate orbital intensity modulations with a low level of counts
during the eclipse. Several models have been proposed to explain the accretion
at different orbital phases by a spherically symmetric stellar wind from the
companion. The aim of this work is to study both the light curve and orbital
phase spectroscopy of this source in the long term. Particularly, the folded
light curve and the changes of the spectral parameters with orbital phase to
analyse the stellar wind of QV Nor, the mass donor of this binary system. We
used all the observations made from the Gas Slit Camera on board MAXI of 4U
1538-52 covering many orbits continuously. We obtained the good interval times
for every orbital phase range which were the input to extract our data. We
estimated the orbital period of the system and then folded the light curves and
we fitted the X-ray spectra with the same model for every orbital phase
spectrum. We also extracted the averaged spectrum of all the MAXI data
available. The MAXI spectra in the 2-20 keV energy range were fitted with an
absorbed Comptonization of cool photons on hot electrons. We found a strong
orbital dependence of the absorption column density but neither the
fluorescence iron emission line nor low energy excess were needed to fit the
MAXI spectra. The variation of the spectral parameters over the binary orbit
were used to examine the mode of accretion onto the neutron star in 4U 1538-52.
We deduce a best value of for QV Nor.Comment: 12 pages, 5 figures, accepted to be published by A&A, corrected typos
(changing bold font to normal one
Classication of Agricultural Fields in Satellite Images Using Two-Dimensional Hidden Markov Models
Image segmentation is a key competence for many real life
applications such as precision agriculture. In this work we present an
approach to classify agricultural fields in noisy satellite images. We start
with the Markovian neighborhood hypothesis from where on we derive a
general two-dimensional hidden Markov model (2D-HMM). To make the
2D-HMM feasible we apply the Path-Constrained Variable-State Viterbi
Algorithm (PCVSVA) which allows us to approximate the optimal hidden state map. We evaluate the PCVSVA for a Landsat image of the
province of C´ordoba, Argentina and a synthetic satellite image. In both
cases we use Cohen’s κb coefficient to compare the PCVSVA and the solution obtained by maximum likelihood (ML) to show the effectiveness
of 2D-HMM of solving image segmentation tasks.Fil: Baumgartner, J. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina.Fil: Giménez, J. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía, Física y Computación; Argentina.Fil: Pucheta, J. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina.Fil: Flesia, A.G. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía, Física y Computación; Argentina.Fil: Flesia, A. G. Universidad Tecnológica Nacional. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina.Sistemas de Automatización y Contro
An XMM-Newton view of FeK{\alpha} in HMXBs
We present a comprehensive analysis of the whole sample of available
XMM-Newton observations of High Mass X-ray Binaries (HMXBs) until August, 2013,
focusing on the FeK{\alpha} emission line. This line is a key tool to better
understand the physical properties of the material surrounding the X-ray source
within a few stellar radii (the circumstellar medium). We have collected
observations from 46 HMXBs, detecting FeK{\alpha} in 21 of them. We have used
the standard classification of HMXBs to divide the sample in different groups.
We find that: (1) FeK{\alpha} is centred at a mean value of 6.42 keV.
Considering the instrumental and fits uncertainties, this value is compatible
with ionization states lower than FeXVIII. (2) The flux of the continuum is
well correlated with the flux of the line, as expected. Eclipse observations
show that the Fe fluorescence emission comes from an extended region
surrounding the X-ray source. (3) FeK{\alpha} is narrow (width lower than
0.15keV), reflecting that the reprocessing material does not move at high
speeds. We attempt to explain the broadness of the line in terms of three
possible broadening phenomena: line blending, Compton scattering and Doppler
shifts (with velocities of the reprocessing material V=1000-2000 km/s). (4) The
equivalent hydrogen column (NH) directly correlates with the EW of FeK{\alpha},
displaying clear similarities to numerical simulations. It highlights the
strong link between the absorbing and the fluorescent matter. The obtained
results clearly point to a very important contribution of the donors wind in
the FeK{\alpha} emission and the absorption when the donor is a supergiant
massive star.Comment: Accepted for publication in A&A. 13 pages, 16 figures + Appendice
A burst with double radio spectrum observed up to 212 GHz
We study a solar flare that occurred on September 10, 2002, in active region
NOAA 10105 starting around 14:52 UT and lasting approximately 5 minutes in the
radio range. The event was classified as M2.9 in X-rays and 1N in H\alpha.
Solar Submillimeter Telescope observations, in addition to microwave data give
us a good spectral coverage between 1.415 and 212 GHz. We combine these data
with ultraviolet images, hard and soft X-rays observations and full-disk
magnetograms. Images obtained from Ramaty High Energy Solar Spectroscopic
Imaging data are used to identify the locations of X-ray sources at different
energies and to determine the X-ray spectrum, while ultra violet images allow
us to characterize the coronal flaring region. The magnetic field evolution of
the active region is analyzed using Michelson Doppler Imager magnetograms. The
burst is detected at all available radio-frequencies. X-ray images (between 12
keV and 300 keV) reveal two compact sources and 212 GHz data, used to estimate
the radio source position, show a single compact source displaced by 25" from
one of the hard X-ray footpoints. We model the radio spectra using two
homogeneous sources, and combine this analysis with that of hard X-rays to
understand the dynamics of the particles. Relativistic particles, observed at
radio wavelengths above 50 GHz, have an electron index evolving with the
typical soft-hard-soft behaviour.Comment: Submitted to Solar Physics, 20 pages, 8 fugure
A calculation of the parameter in the static limit
We calculate the parameter, relevant for --
mixing, from a lattice gauge theory simulation at . The bottom
quarks are simulated in the static theory, the light quarks with Wilson
fermions. Improved smearing functions produced by a variational technique,
MOST, are used to reduce statistical errors and minimize excited-state
contamination of the ground-state signal. We obtain (statistical) (systematic) which corresponds to
(statistical) (systematic) for
the one-loop renormalization-scheme-independent parameter. The systematic
errors include the uncertainty due to alternative (less favored) treatments of
the perturbatively-calculated mixing coefficients; this uncertainty is at least
as large as residual differences between Wilson-static and clover-static
results. Our result agrees with extrapolations of results from relativistic
(Wilson) heavy quark simulations.Comment: 39 pages (REVTeX) including 10 figures (PostScript); Final version
accepted for publication: Added new section for clarity; Included comparison
to recent results by other groups; slight numerical changes; Essential
conclusions remain the sam
Non-perturbative renormalization of lattice operators in coordinate space
We present the first numerical implementation of a non-perturbative
renormalization method for lattice operators, based on the study of correlation
functions in coordinate space at short Euclidean distance. The method is
applied to compute the renormalization constants of bilinear quark operators
for the non-perturbative O(a)-improved Wilson action in the quenched
approximation. The matching with perturbative schemes, such as MS-bar, is
computed at the next-to-leading order in continuum perturbation theory. A
feasibility study of this technique with Neuberger fermions is also presented.Comment: 11 pages and 9 figures, LaTeX2
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