6,657 research outputs found
Entanglement, BEC, and superfluid-like behavior of two-mode photon systems
A system of two interacting photon modes, without constraints on the photon
number, in the presence of a Kerr nonlinearity, exhibits BEC if the transfer
amplitude is greater than the mode frequency. A symmetry-breaking field (SBF)
can be introduced by taking into account a classical electron current. The
ground state, in the limit of small nonlinearity, becomes a squeezed state, and
thus the modes become entangled. The smaller is the SBF, the greater is
entanglement. Superfluid-like behavior is observed in the study of entanglement
growth from an initial coherent state, since in the short-time range the growth
does not depend on the SBF amplitude, and on the initial state amplitude. On
the other hand, the latter is the only parameter which determines entanglement
in the absence of the SBF
A systematic analysis of X-ray afterglows of gamma-ray burst observed by XMM-Newton
This work is part of a systematic re-analysis program of all the data of
Gamma-Ray Burst (GRB) X-ray afterglows observed so far, in order to constrain
the GRB models. We present here a systematic analysis of those afterglows
observed by XMM-Newton between January 2000 and March 2004. This dataset
includes GRB 011211 and GRB 030329. We have obtained spectra, light curves and
colors for these afterglows. In this paper we focus on the continuum spectral
and temporal behavior. We compare these values with the theoretical ones
expected from the fireball model. We derive constraints about the burst
environment (absorption, density profile) and put constraints on their beaming
angle.Comment: 7 pages, 2 figures, COSPAR proceeding accepted for publication in
Advances in Space Researc
A Correlation Between the Intrinsic Brightness and Average Decay Rate of Gamma-ray Burst X-ray Afterglow Light Curves
We present a correlation between the average temporal decay
({\alpha}X,avg,>200s) and early-time luminosity (LX,200s) of X-ray afterglows
of gamma-ray bursts as observed by Swift-XRT. Both quantities are measured
relative to a rest frame time of 200 s after the {\gamma}-ray trigger. The
luminosity average decay correlation does not depend on specific temporal
behavior and contains one scale independent quantity minimizing the role of
selection effects. This is a complementary correlation to that discovered by
Oates et al. (2012) in the optical light curves observed by Swift-UVOT. The
correlation indicates that on average, more luminous X-ray afterglows decay
faster than less luminous ones, indicating some relative mechanism for energy
dissipation. The X-ray and optical correlations are entirely consistent once
corrections are applied and contamination is removed. We explore the possible
biases introduced by different light curve morphologies and observational
selection effects, and how either geometrical effects or intrinsic properties
of the central engine and jet could explain the observed correlation.Comment: Accepted for Publication in ApJ; 16 pages, 15 figures, 2 table
Diversity of Rainfall Thresholds for early warning of hydro-geological disasters
Abstract. For early warning of disasters induced by precipitation (such as floods and landslides), different kinds of rainfall thresholds are adopted, which vary from each other, on the basis on adopted hypotheses. In some cases, they represent the occurrence probability of an event (landslide or flood), in other cases the exceedance probability of a critical value for an assigned indicator I (a function of rainfall heights), and in further cases they only indicate the exceeding of a prefixed percentage a critical value for I, indicated as Icr. For each scheme, it is usual to define three different criticality levels (ordinary, moderate and severe), which are associated to warning levels, according to emergency plans. This work briefly discusses different schemes of rainfall thresholds, focusing attention on landslide prediction, with some applications to a real case study in Calabria region (southern Italy)
Reconstruction of time-dependent coefficients: a check of approximation schemes for non-Markovian convolutionless dissipative generators
We propose a procedure to fully reconstruct the time-dependent coefficients
of convolutionless non-Markovian dissipative generators via a finite number of
experimental measurements. By combining a tomography based approach with a
proper data sampling, our proposal allows to relate the time-dependent
coefficients governing the dissipative evolution of a quantum system to
experimentally accessible quantities. The proposed scheme not only provides a
way to retrieve full information about potentially unknown dissipative
coefficients but also, most valuably, can be employed as a reliable consistency
test for the approximations involved in the theoretical derivation of a given
non-Markovian convolutionless master equation.Comment: 11 pages, 4 figures, revised version published on PR
Air Mass Frequency During Precipitation Events in the Northern Plains of the United States
Since 1980, numerous billion-dollar disasters have affected the Northern Plains of the United States, including nine droughts and four floods. The atmospheric environment present during precipitation events can largely be described by the presiding air mass conditions since air masses characterize a multitude of meteorological variables at one time over a large region. The goal of this research is to add knowledge to current understandings of the factors responsible for precipitation in the Northern Plains through an assessment of synoptic air mass conditions. The Spatial Synoptic Classification is used to categorize 30 years of daily surface air mass types across the region alongside precipitation from the United States Historical Climatological Network. Annual and seasonal air mass frequencies are examined for all precipitation events. Precipitation days are also examined by intensity. Results indicate that the Transitional air mass, associated with changing air mass conditions commonly related to passing fronts, is not the leading producer of rainfall in the region. All moist air mass varieties are generally more dominant during precipitation events and the Moist Moderate (MM) and Moist Polar (MP) air masses are frequently responsible for half of all rainfall in the region. MM and MP tend to be particularly prominent during the winter season. The MM and Moist Tropical air masses dominate around 65% of summer precipitation events. Interestingly, there is a tendency for precipitation while dry air masses are present to the north and west within the study region
On the nature of X-Ray Flashes in the SWIFT era
X-Ray Flashes (XRFs) are soft gamma-ray bursts whose nature is not clear.
Their soft spectrum can be due to cosmological effects (high redshift), an
off-axis view of the jet or can be intrinsic to the source. We use SWIFT
observations to investigate different scenarios proposed to explain their
origin. We have made a systematic analysis of the afterglows of XRFs with known
redshift observed by SWIFT. We derive their redshift and luminosity
distributions, and compare their properties with a sample of normal GRBs
observed by the same instrument. The high distance hypothesis is ruled out by
the redshift distribution of our sample of XRFs, indicating that, at least for
our sample, the off-axis and sub-energetic hypotheses are preferred. Of course,
this does not exclude that some XRFs without known redshift could be at high
distance. However we find that taking into account the sensitivity of the BAT
instrument, XRFs cannot be detected by SWIFT beyond ~ 3. The luminosity
distribution of XRF afterglows is similar to the GRB one. This would rule out
most off-axis models, but for the homogeneous jet model. However this model
predicts a GRB rate uncomfortably near the observed rate of supernovae. This
implies that XRFs, at least those of our sample, are intrinsically soft.Comment: 4 pages, 2 color figures. Astronomy and Astrophysics Letters,
accepte
Multi-wavelength analysis of the field of the dark burst GRB 031220
We have collected and analyzed data taken in different spectral bands (from
X-ray to optical and infrared) of the field of GRB031220 and we present results
of such multiband observations. Comparison between images taken at different
epochs in the same filters did not reveal any strong variable source in the
field of this burst. X-ray analysis shows that only two of the seven Chandra
sources have a significant flux decrease and seem to be the most likely
afterglow candidates. Both sources do not show the typical values of the R-K
colour but they appear to be redder. However, only one source has an X-ray
decay index (1.3 +/- 0.1) that is typical for observed afterglows. We assume
that this source is the best afterglow candidate and we estimate a redshift of
1.90 +/- 0.30. Photometric analysis and redshift estimation for this object
suggest that this GRB can be classified as a Dark Burst and that the
obscuration is the result of dust extinction in the circum burst medium or
inside the host galaxy.Comment: 7 pages, 5 figures, accepted for publication on A&
The ultra-long GRB 111209A - II. Prompt to afterglow and afterglow properties
The "ultra-long" Gamma Ray Burst GRB 111209A at redshift z=0.677, is so far
the longest GRB ever observed, with rest frame prompt emission duration of ~4
hours. In order to explain the bursts exceptional longevity, a low metallicity
blue supergiant progenitor has been invoked. In this work, we further
investigate this peculiar burst by performing a multi-band temporal and
spectral analysis of both the prompt and the afterglow emission. We use
proprietary and publicly available data from Swift, Konus Wind, XMM-Newton,
TAROT as well as from other ground based optical and radio telescopes. We find
some peculiar properties that are possibly connected to the exceptional nature
of this burst, namely: i) an unprecedented large optical delay of 410+/-50 s is
measured between the peak epochs of a marked flare observed also in gamma-rays
after about 2 ks from the first Swift/BAT trigger; ii) if the optical and
X-ray/gamma-ray photons during the prompt emission share a common origin, as
suggested by their similar temporal behavior, a certain amount of dust in the
circumburst environment should be introduced, with rest frame visual dust
extinction of AV=0.3-1.5 mag; iii) at the end of the X-ray "steep decay phase"
and before the start of the X-ray afterglow, we detect the presence of a hard
spectral extra power law component never revealed so far. On the contrary, the
optical afterglow since the end of the prompt emission shows more common
properties, with a flux power law decay with index alpha=1.6+/-0.1 and a late
re-brightening feature at 1.1 day. We discuss our findings in the context of
several possible interpretations given so far to the complex multi-band GRB
phenomenology. We also attempt to exploit our results to further constrain the
progenitor nature properties of this exceptionally long GRB, suggesting a
binary channel formation for the proposed blue supergiant progenitor.Comment: ApJ accepted. Revised version with substantial adjustments, the main
results remain unchange
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