6,657 research outputs found

    Entanglement, BEC, and superfluid-like behavior of two-mode photon systems

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    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

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    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

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    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

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    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

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    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

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    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

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    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

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    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

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    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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