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Sample records for afterglow modeling based

  1. Simulation and physical model based gamma-ray burst afterglow analysis

    NASA Astrophysics Data System (ADS)

    van Eerten, H. J.

    2015-09-01

    Advances in our numerical and theoretical understanding of gamma-ray burst afterglow processes allow us to construct models capable of dealing with complex relativistic jet dynamics and non-thermal emission, that can be compared directly to data from instruments such as Swift. Because afterglow blast waves and power law spectra are intrinsically scale-invariant under changes of explosion energy and medium density, templates can be generated from large-scale hydrodynamics simulations. This allows for iterative template-based model fitting using the physical model parameters (quantifying the properties of the burster, emission and observer) directly as fit variables. Here I review how such an approach to afterglow analysis works in practice, paying special attention to the underlying model assumptions, possibilities, caveats and limitations of this type of analysis. Because some model parameters can be degenerate in certain regions of parameter space, or unconstrained if data in a limited number of a bands is available, a Bayesian approach is a natural fit. The main features of the standard afterglow model are reviewed in detail.

  2. GRB050525A : Multiband modelling of the afterglow

    NASA Astrophysics Data System (ADS)

    Resmi, Lekshmi; Misra, Kuntal; Castro-Tirado, Alberto

    2011-08-01

    The Swift era has posed a challenge to the standard blast-wave model of Gamma Ray Burst afterglows. The achromatic steepening of the afterglow lightcurves (`jet break') considered in the model as the signature of outflow collimation, has become almost rare. Several afterglows exhibited complex lightcurves that did not confirm by the predicted spectral--temporal `closure relations' of the blastwave model. Here we present optical observations and broadband modelling of the afterglow of GRB0505025A, a bright burst detected and followed up by Swift. We find that the overall evolution of the afterglow can not be explained by a single forward shock emission, though the late time evolution is compatible with the predictions of the standard afterglow model, including a jet break. We explain the afterglow evolution based on a two-component jet model and estimate the physical parameters.

  3. The Supercritical Pile GRB Model: The Prompt to Afterglow Evolution

    NASA Technical Reports Server (NTRS)

    Kazanas, Demosthenes

    2008-01-01

    The 'Supercritical Pile' is a very economical gamma ray burst (GRB) model that provides for the efficient conversion of the energy stored in the protons of a Relativistic Blast Wave (RBW) into radiation and at the same time produces - in the prompt GRB phase, even in the absence of any particle acceleration - a spectral peak at an energy sim 1 MeV. We extend this model to include also the evolution of the RBW Lorentz factor Gamma and thus follow the spectral and temporal features of this model into the early GRB afterglow stage. One of the novel features of the present treatment is the inclusion of the feedback of the GRB produced radiation on the evolution of Gamma with radius. This feedback and the presence of kinematic and dynamic thresholds in the model can be the sources of rich time evolution which we have begun to explore. In particular, one can this way obtain afterglow light curves with steep decays followed by the more conventional flatter afterglow slopes, while at the same time preserving the desirable features of the model, i.e. the well defined relativistic electron source and radiative processes that produce the proper peak in the nu F spectra. Furthermore, the existence of a kinematic threshold in this model provides for a operational distinction of the prompt and afterglow GRB stages; in fact, the afterglow stage sets in when the RBW Lorentz factor cannot anymore fulfill the kinematic condition for pair formation in the photon - proton pair production reactions that constitute the fundamental process for the dissipation of the blast wave kinetic energy. We present the results of a specific set of parameters of this model with emphasis on the multiwavelength prompt emission and transition to the early afterglow.

  4. The Supercritical Pile GRB Model: The Prompt to Afterglow Evolution

    NASA Technical Reports Server (NTRS)

    Mastichiadis, A.; Kazanas, D.

    2009-01-01

    The "Supercritical Pile" is a very economical GRB model that provides for the efficient conversion of the energy stored in the protons of a Relativistic Blast Wave (RBW) into radiation and at the same time produces - in the prompt GRB phase, even in the absence of any particle acceleration - a spectral peak at energy approx. 1 MeV. We extend this model to include the evolution of the RBW Lorentz factor Gamma and thus follow its spectral and temporal features into the early GRB afterglow stage. One of the novel features of the present treatment is the inclusion of the feedback of the GRB produced radiation on the evolution of Gamma with radius. This feedback and the presence of kinematic and dynamic thresholds in the model can be the sources of rich time evolution which we have began to explore. In particular. one can this may obtain afterglow light curves with steep decays followed by the more conventional flatter afterglow slopes, while at the same time preserving the desirable features of the model, i.e. the well defined relativistic electron source and radiative processes that produce the proper peak in the (nu)F(sub nu), spectra. In this note we present the results of a specific set of parameters of this model with emphasis on the multiwavelength prompt emission and transition to the early afterglow.

  5. Testing Models for the Shallow Decay Phase of Gamma-Ray Burst Afterglows with Polarization Observations

    NASA Astrophysics Data System (ADS)

    Lan, Mi-Xiang; Wu, Xue-Feng; Dai, Zi-Gao

    2016-08-01

    The X-ray afterglows of almost one-half of gamma-ray bursts have been discovered by the Swift satellite to have a shallow decay phase of which the origin remains mysterious. Two main models have been proposed to explain this phase: relativistic wind bubbles (RWBs) and structured ejecta, which could originate from millisecond magnetars and rapidly rotating black holes, respectively. Based on these models, we investigate polarization evolution in the shallow decay phase of X-ray and optical afterglows. We find that in the RWB model, a significant bump of the polarization degree evolution curve appears during the shallow decay phase of both optical and X-ray afterglows, while the polarization position angle abruptly changes its direction by 90°. In the structured ejecta model, however, the polarization degree does not evolve significantly during the shallow decay phase of afterglows whether the magnetic field configuration in the ejecta is random or globally large-scale. Therefore, we conclude that these two models for the shallow decay phase and relevant central engines would be testable with future polarization observations.

  6. Modeling Extragalactic Extinction through Gamma-Ray Burst Afterglows

    NASA Astrophysics Data System (ADS)

    Zonca, Alberto; Cecchi-Pestellini, Cesare; Mulas, Giacomo; Casu, Silvia; Aresu, Giambattista

    2016-09-01

    We analyze extragalactic extinction profiles derived through gamma-ray burst afterglows, using a dust model specifically constructed on the assumption that dust grains are not immutable but respond, time-dependently, to the local physics. Such a model includes core-mantle spherical particles of mixed chemical composition (silicate core, sp2, and sp3 carbonaceous layers), and an additional molecular component in the form of free-flying polycyclic aromatic hydrocarbons. We fit most of the observed extinction profiles. Failures occur for lines of sight, presenting remarkable rises blueward of the bump. We find a tendency for the carbon chemical structure to become more aliphatic with the galactic activity, and to some extent with increasing redshifts. Moreover, the contribution of the molecular component to the total extinction is more important in younger objects. The results of the fitting procedure (either successes and failures) may be naturally interpreted through an evolutionary prescription based on the carbon cycle in the interstellar medium of galaxies.

  7. CALORIMETRY OF GRB 030329: SIMULTANEOUS MODEL FITTING TO THE BROADBAND RADIO AFTERGLOW AND THE OBSERVED IMAGE EXPANSION RATE

    SciTech Connect

    Mesler, Robert A.; Pihlstroem, Ylva M.

    2013-09-01

    We perform calorimetry on the bright gamma-ray burst GRB 030329 by fitting simultaneously the broadband radio afterglow and the observed afterglow image size to a semi-analytic MHD and afterglow emission model. Our semi-analytic method is valid in both the relativistic and non-relativistic regimes, and incorporates a model of the interstellar scintillation that substantially effects the broadband afterglow below 10 GHz. The model is fitted to archival measurements of the afterglow flux from 1 day to 8.3 yr after the burst. Values for the initial burst parameters are determined and the nature of the circumburst medium is explored. Additionally, direct measurements of the lateral expansion rate of the radio afterglow image size allow us to estimate the initial Lorentz factor of the jet.

  8. Applying an accurate spherical model to gamma-ray burst afterglow observations

    NASA Astrophysics Data System (ADS)

    Leventis, K.; van der Horst, A. J.; van Eerten, H. J.; Wijers, R. A. M. J.

    2013-05-01

    We present results of model fits to afterglow data sets of GRB 970508, GRB 980703 and GRB 070125, characterized by long and broad-band coverage. The model assumes synchrotron radiation (including self-absorption) from a spherical adiabatic blast wave and consists of analytic flux prescriptions based on numerical results. For the first time it combines the accuracy of hydrodynamic simulations through different stages of the outflow dynamics with the flexibility of simple heuristic formulas. The prescriptions are especially geared towards accurate description of the dynamical transition of the outflow from relativistic to Newtonian velocities in an arbitrary power-law density environment. We show that the spherical model can accurately describe the data only in the case of GRB 970508, for which we find a circumburst medium density n ∝ r-2. We investigate in detail the implied spectra and physical parameters of that burst. For the microphysics we show evidence for equipartition between the fraction of energy density carried by relativistic electrons and magnetic field. We also find that for the blast wave to be adiabatic, the fraction of electrons accelerated at the shock has to be smaller than 1. We present best-fitting parameters for the afterglows of all three bursts, including uncertainties in the parameters of GRB 970508, and compare the inferred values to those obtained by different authors.

  9. The Gamma-Ray Burst Afterglow Modeling Project: Foundational Statistics and Absorption & Extinction Models

    NASA Astrophysics Data System (ADS)

    Trotter, Adam Somers

    The Gamma-Ray Burst (GRB) Afterglow Modeling Project (AMP) will model, in a statistically sound and self-consistent way, every GRB afterglow observed since the first detection in 1997, using all available radio, infrared, optical, ultraviolet and X-ray data. The result will be a catalog of fitted empirical model parameters describing the intrinsic afterglow emission, and extinction due to dust and absorption due to gas along the line of sight to the GRB. This ever-growing catalog of fitted model parameters will allow us to infer the astrophysical properties of GRBs and their environments, and to explore their variety and evolution over the history of the universe. First, I present a new, broadly applicable statistical technique, the TRF statistic, for fitting model distributions to data in two dimensions, where the data have intrinsic uncertainties in both dimensions, and extrinsic scatter in both dimensions that is greater than can be accounted for by the intrinsic uncertainties alone. I demonstrate the properties of the TRF statistic, which is invertible but not scalable, and present an algorithm for obtaining an optimum scale for fits to a given data set. I then apply the TRF statistic to observations of interstellar extinction of stars along various Milky Way and Magellanic Cloud lines of sight, and to observations of Lyalpha forest flux deficits in quasars, to construct a comprehensive empirical model for extinction due to interstellar dust in the source frame and in the Milky Way, and absorption due to gas in the source frame and in the intergalactic medium. Combined with theoretical models of synchrotron emission from GRB jets, the resulting parameterization provides a framework for modeling the observed emission from most GRB afterglows. Furthermore, the extinction and absorption models are broadly applicable, in that they may be used to model observations of any extragalactic point source of radiation. Finally, I describe the results of model fitting to

  10. Gas Phase Model of Surface Reactions for N{2} Afterglows

    NASA Astrophysics Data System (ADS)

    Marković, V. Lj.; Petrović, Z. Lj.; Pejović, M. M.

    1996-07-01

    The adequacy of the homogeneous gas phase model as a representation of the surface losses of diffusing active particles in gas phase is studied. As an example the recent data obtained for the surface recombination coefficients are reanalyzed. The data were obtained by the application of the breakdown delay times which consists of the measurements of the breakdown delay times t_d as a function of the afterglow period tau. It was found that for the conditions of our experiment, the diffusion should not be neglected as the final results are significantly different when obtained by approximate gas phase representation and by exact numerical solution to the diffusion equation. While application of the gas phase effective coefficients to represent surface losses gives an error in the value of the recombination coefficient, it reproduces correctly other characteristics such as order of the process which can be obtained from simple fits to the experimental data. Dans cet article, nous étudions la validité du modèle approximatif représentant les pertes superficielles des particules actives qui diffusent de la phase gazeuse comme pertes dans la phase homogène du gaz. Les données actuelles du coefficient de recombination en surface sont utilisées par cette vérification . Les données experimentales sont obtenues en utilisant la technique qui consiste en la mesure du temps de retard du début de la décharge en fonction de la période de relaxation. Nous avons trouvé que, pour nos conditions expérimentales, la diffusion ne peut être négligée. Aussi, les résultats finals sont considérablement différents quand ils sont obtenus en utilisant le modèle approximatif par comparaison aves les résultats obtenus par la solution numérique exacte de l'équation de la diffusion. L'application des coefficients effectifs dans la phase gaseuse pour la présentation des pertes superficielles donne, pour les coefficients de la recombinaison, des valeurs qui diffèrent en

  11. Afterglow Complex Plasma

    SciTech Connect

    Samarian, A. A.; Boufendi, L.; Mikikian, M.

    2008-09-07

    The review of the first detailed experimental and theoretical studies of complex plasma in RF discharge afterglow is presented. The studies have been done in a frame of FAST collaborative research project between Complex Plasma Laboratory of the University of Sydney and the GREMI laboratory of Universite d'Orleans. We examined the existing models of plasma decay, presents experimental observations of dust dynamics under different afterglow complex plasma conditions, presents the experimental data obtained (in particular the presence of positively charged particles in discharge afterglow), discusses the use of dust particles as a probe to study the diffusion losses in afterglow plasmas.

  12. Prior Emission Model for X-ray Plateau Phase of Gamma-Ray Burst Afterglows

    NASA Astrophysics Data System (ADS)

    Yamazaki, Ryo

    2009-01-01

    The two-component emission model to explain the plateau phase of the X-ray afterglows of gamma-ray bursts (GRBs) is proposed. One component, which is responsible for the plateau and subsequent normal decay phase of the X-ray afterglow, is the prior emission via outflow ejected from the central engine before the main burst. The other is the main outflow, which causes the prompt GRB emission and the initial steep decay phase of the X-ray afterglow. In this model, the transition from the plateau to the subsequent normal decay phase is an artifact of the choice of the zero of time. For events with distinct plateau phase, the central engine is active 103-104 s before the launch of the main outflow. According to this model, a prior emission in the X-ray and/or optical bands 103-104 s before the prompt GRB emission is possibly seen, which will be tested by near-future instruments such as Monitor of All-sky X-ray Image (MAXI), WIDe-field telescope for GRB Early Timing (WIDGET), and so on.

  13. Radio observations of GRB 100418a: Test of an energy injection model explaining long-lasting GRB afterglows

    SciTech Connect

    Moin, A.; Wang, Z.; Chandra, P.; Miller-Jones, J. C. A.; Tingay, S. J.; Reynolds, C.; Taylor, G. B.; Frail, D. A.; Phillips, C. J.

    2013-12-20

    We present the results of our radio observational campaign of gamma-ray burst (GRB) 100418a, for which we used the Australia Telescope Compact Array, the Very Large Array, and the Very Long Baseline Array. GRB 100418a was a peculiar GRB with unusual X-ray and optical afterglow profiles featuring a plateau phase with a very shallow rise. This observed plateau phase was believed to be due to a continued energy injection mechanism that powered the forward shock, giving rise to an unusual and long-lasting afterglow. The radio afterglow of GRB 100418a was detectable several weeks after the prompt emission. We conducted long-term monitoring observations of the afterglow and attempted to test the energy injection model advocating that the continuous energy injection is due to shells of material moving at a wide range of Lorentz factors. We obtained an upper limit of γ < 7 for the expansion rate of the GRB 100418a radio afterglow, indicating that the range-of-Lorentz factor model could only be applicable for relatively slow-moving ejecta. A preferred explanation could be that continued activity of the central engine may have powered the long-lasting afterglow.

  14. Spectral softening in the X-RAY afterglow of GRB 130925A as predicted by the dust scattering model

    SciTech Connect

    Zhao, Yi-Nan; Shao, Lang

    2014-07-01

    Gamma-ray bursts (GRBs) usually occur in a dense star-forming region with a massive circumburst medium. The small-angle scattering of intense prompt X-ray emission off the surrounding dust grains will have observable consequences and sometimes can dominate the X-ray afterglow. In most of the previous studies, only the Rayleigh-Gans (RG) approximation is employed for describing the scattering process, which works accurately for the typical size of grains (with radius of a ≤ 0.1 μm) in the diffuse interstellar medium. When the size of the grains may significantly increase, as in a more dense region where GRBs would occur, the RG approximation may not be valid enough for modeling detailed observational data. In order to study the temporal and spectral properties of the scattered X-ray emission more accurately with potentially larger dust grains, we provide a practical approach using the series expansions of anomalous diffraction (AD) approximation based on the complicated Mie theory. We apply our calculations to understand the puzzling X-ray afterglow of recently observed GRB 130925A that showed a significant spectral softening. We find that the X-ray scattering scenarios with either AD or RG approximation adopted could well reproduce both the temporal and spectral profile simultaneously. Given the plateau present in the early X-ray light curve, a typical distribution of smaller grains as in the interstellar medium would be suggested for GRB 130925A.

  15. Spectral Softening in the X-Ray Afterglow of GRB 130925A as Predicted by the Dust Scattering Model

    NASA Astrophysics Data System (ADS)

    Zhao, Yi-Nan; Shao, Lang

    2014-07-01

    Gamma-ray bursts (GRBs) usually occur in a dense star-forming region with a massive circumburst medium. The small-angle scattering of intense prompt X-ray emission off the surrounding dust grains will have observable consequences and sometimes can dominate the X-ray afterglow. In most of the previous studies, only the Rayleigh-Gans (RG) approximation is employed for describing the scattering process, which works accurately for the typical size of grains (with radius of a <= 0.1 μm) in the diffuse interstellar medium. When the size of the grains may significantly increase, as in a more dense region where GRBs would occur, the RG approximation may not be valid enough for modeling detailed observational data. In order to study the temporal and spectral properties of the scattered X-ray emission more accurately with potentially larger dust grains, we provide a practical approach using the series expansions of anomalous diffraction (AD) approximation based on the complicated Mie theory. We apply our calculations to understand the puzzling X-ray afterglow of recently observed GRB 130925A that showed a significant spectral softening. We find that the X-ray scattering scenarios with either AD or RG approximation adopted could well reproduce both the temporal and spectral profile simultaneously. Given the plateau present in the early X-ray light curve, a typical distribution of smaller grains as in the interstellar medium would be suggested for GRB 130925A.

  16. The Supercritical Pile Gamma-Ray Burst Model: The GRB Afterglow Steep Decline and Plateau Phase

    NASA Technical Reports Server (NTRS)

    Sultana, Joseph; Kazanas, D.; Mastichiadis, A.

    2013-01-01

    We present a process that accounts for the steep decline and plateau phase of the Swift X-Ray Telescope (XRT) light curves, vexing features of gamma-ray burst (GRB) phenomenology. This process is an integral part of the "supercritical pile" GRB model, proposed a few years ago to account for the conversion of the GRB kinetic energy into radiation with a spectral peak at E(sub pk) is approx. m(sub e)C(exp 2). We compute the evolution of the relativistic blast wave (RBW) Lorentz factor Gamma to show that the radiation-reaction force due to the GRB emission can produce an abrupt, small (approx. 25%) decrease in Gamma at a radius that is smaller (depending on conditions) than the deceleration radius R(sub D). Because of this reduction, the kinematic criticality criterion of the "supercritical pile" is no longer fulfilled. Transfer of the proton energy into electrons ceases and the GRB enters abruptly the afterglow phase at a luminosity smaller by approx. m(sub p)/m(sub e) than that of the prompt emission. If the radius at which this slow-down occurs is significantly smaller than R(sub D), the RBW internal energy continues to drive the RBW expansion at a constant (new) Gamma and its X-ray luminosity remains constant until R(sub D) is reached, at which point it resumes its more conventional decay, thereby completing the "unexpected" XRT light curve phase. If this transition occurs at R is approx. equal to R(sub D), the steep decline is followed by a flux decrease instead of a "plateau," consistent with the conventional afterglow declines. Besides providing an account of these peculiarities, the model suggests that the afterglow phase may in fact begin before the RBW reaches R is approx. equal to R(sub D), thus providing novel insights into GRB phenomenology.

  17. The Supercritical Pile Gamma-Ray Burst Model: The GRB Afterglow Steep Decline and Plateau Phase

    NASA Astrophysics Data System (ADS)

    Sultana, J.; Kazanas, D.; Mastichiadis, A.

    2013-12-01

    We present a process that accounts for the steep decline and plateau phase of the Swift X-Ray Telescope (XRT) light curves, vexing features of gamma-ray burst (GRB) phenomenology. This process is an integral part of the "supercritical pile" GRB model, proposed a few years ago to account for the conversion of the GRB kinetic energy into radiation with a spectral peak at E pk ~ mec 2. We compute the evolution of the relativistic blast wave (RBW) Lorentz factor Γ to show that the radiation-reaction force due to the GRB emission can produce an abrupt, small (~25%) decrease in Γ at a radius that is smaller (depending on conditions) than the deceleration radius RD . Because of this reduction, the kinematic criticality criterion of the "supercritical pile" is no longer fulfilled. Transfer of the proton energy into electrons ceases and the GRB enters abruptly the afterglow phase at a luminosity smaller by ~mp /me than that of the prompt emission. If the radius at which this slow-down occurs is significantly smaller than RD , the RBW internal energy continues to drive the RBW expansion at a constant (new) Γ and its X-ray luminosity remains constant until RD is reached, at which point it resumes its more conventional decay, thereby completing the "unexpected" XRT light curve phase. If this transition occurs at R ~= RD , the steep decline is followed by a flux decrease instead of a "plateau," consistent with the conventional afterglow declines. Besides providing an account of these peculiarities, the model suggests that the afterglow phase may in fact begin before the RBW reaches R ~= RD , thus providing novel insights into GRB phenomenology.

  18. Rapid electron density decay observed by surface-wave probe in afterglow of pulsed fluorocarbon-based plasma

    NASA Astrophysics Data System (ADS)

    Ohya, Yoshinobu; Iwata, Manabu; Ishikawa, Kenji; Sekine, Makoto; Hori, Masaru; Sugai, Hideo

    2016-08-01

    To elucidate the pulsed fluorocarbon plasma behavior, a surface-wave probe with high time resolution was used to measure the electron density n e in the afterglow of plasma. In a dual-frequency capacitively coupled plasma of fluorocarbon chemistry, e.g., an O2-based C4F6 and Ar mixture, n e vanished rapidly in a short time (∼5 µs), whilst the dc current flowing onto the top electrode biased at ‑300 V decreased very slowly (decay time ∼70 µs). This observation is clear evidence of ion–ion plasma formation by electron attachment in the afterglow. We point out that the electron attachment rates for fluorocarbon radicals significantly affect the electrons and ion–ion plasma behaviors observed at the afterglow phase.

  19. Effect of secondary emission on the argon plasma afterglow with large dust density

    SciTech Connect

    Denysenko, I. B.; Azarenkov, N. A.; Burmaka, G. P.; Stefanović, I.

    2015-02-15

    A zero-dimensional, space-averaged model for argon plasma afterglow with large dust density is developed. In the model, three groups of electrons in the plasma afterglow are assumed: (i) thermal electrons with Maxwellian distribution, (ii) energetic electrons generated by metastable-metastable collisions (metastable pooling), and (iii) secondary electrons generated at collisions of ions with the electrodes, which have sufficiently large negative voltages in the afterglow. The model calculates the time-dependencies for electron densities in plasma afterglow based on experimental decay times for metastable density and electrode bias. The effect of secondary emission on electron density in the afterglow is estimated by varying secondary emission yields. It is found that this effect is less important than metastable pooling. The case of dust-free plasma afterglow is considered also, and it is found that in the afterglow the effect of secondary emission may be more important than metastable pooling. The secondary emission may increase thermal electron density n{sub e} in dust-free and dusty plasma afterglows on a few ten percentages. The calculated time dependencies for n{sub e} in dust-free and dusty plasma afterglows describe well the experimental results.

  20. Growth of graphene-based films using afterglow of inductively coupled plasma

    NASA Astrophysics Data System (ADS)

    Hiramatsu, Mineo; Tomatsu, Masakazu; Kondo, Hiroki; Hori, Masaru

    2014-10-01

    Plasma-enhanced CVD (PECVD) employing methane/hydrogen gases has been used to grow diamond and carbon nanostructures. In the case of graphene growth using PECVD, excessive supply of carbon precursors and ion bombardment on the growing surface would cause secondary nuclei, resulting in small size of graphene grain and degradation in crystallinity. To overcome this issue, in this work, afterglow of inductively coupled plasma (ICP) was used for the growth of graphene. The CVD system is simple and consists of a reaction chamber and a remote radical source that uses an ICP in cylindrical geometry. Methane/hydrogen gases were fed through a quartz tube of 26 mm inner diameter and 20 cm in length. A five-turn rf (13.56 MHz) coil was mounted on the quartz tube. Substrates (Ni-coated Si and Cu foil) were located in the afterglow region of ICP. Growth experiments were carried out for 1-10 min at temperature of 700 C, rf power of 400 W, and total pressure of 100 mTorr. We have successfully fabricated graphene-based films, which was confirmed by the Raman spectrum and SEM image of deposit. We will discuss the planar graphene growth mechanism in terms of precursors and their surface reaction, in conjunction with the growth experiments using microwave plasma and ICP in planar geometry.

  1. Detailed afterglow modelling and host galaxy properties of the dark GRB 111215A

    NASA Astrophysics Data System (ADS)

    van der Horst, A. J.; Levan, A. J.; Pooley, G. G.; Wiersema, K.; Krühler, T.; Perley, D. A.; Starling, R. L. C.; Curran, P. A.; Tanvir, N. R.; Wijers, R. A. M. J.; Strom, R. G.; Kouveliotou, C.; Hartoog, O. E.; Xu, D.; Fynbo, J. P. U.; Jakobsson, P.

    2015-02-01

    Gamma-ray burst (GRB) 111215A was bright at X-ray and radio frequencies, but not detected in the optical or near-infrared (nIR) down to deep limits. We have observed the GRB afterglow with the Westerbork Synthesis Radio Telescope and Arcminute Microkelvin Imager at radio frequencies, with the William Herschel Telescope and Nordic Optical Telescope in the nIR/optical, and with the Chandra X-ray Observatory. We have combined our data with the Swift X-Ray Telescope monitoring, and radio and millimetre observations from the literature to perform broad-band modelling, and determined the macro- and microphysical parameters of the GRB blast wave. By combining the broad-band modelling results with our nIR upper limits we have put constraints on the extinction in the host galaxy. This is consistent with the optical extinction we have derived from the excess X-ray absorption, and higher than in other dark bursts for which similar modelling work has been performed. We also present deep imaging of the host galaxy with the Keck I telescope, Spitzer Space Telescope, and Hubble Space Telescope (HST), which resulted in a well-constrained photometric redshift, giving credence to the tentative spectroscopic redshift we obtained with the Keck II telescope, and estimates for the stellar mass and star formation rate of the host. Finally, our high-resolution HST images of the host galaxy show that the GRB afterglow position is offset from the brightest regions of the host galaxy, in contrast to studies of optically bright GRBs.

  2. Modeling the Early Afterglow in the Short and Hard GRB 090510

    NASA Astrophysics Data System (ADS)

    Fraija, N.; Lee, W. H.; Veres, P.; Barniol Duran, R.

    2016-11-01

    The bright, short, and hard GRB 090510 was detected by all instruments aboard the Fermi and Swift satellites. The multiwavelength observations of this burst presented similar features to the Fermi-LAT-detected gamma-ray bursts. In the framework of the external shock model of early afterglow, a leptonic scenario that evolves in a homogeneous medium is proposed to revisit GRB 090510 and explain the multiwavelength light curve observations presented in this burst. These observations are consistent with the evolution of a jet before and after the jet break. The long-lasting LAT, X-ray, and optical fluxes are explained in the synchrotron emission from the adiabatic forward shock. Synchrotron self-Compton emission from the reverse shock is consistent with the bright LAT peak provided that the progenitor environment is entrained with strong magnetic fields. It could provide compelling evidence of magnetic field amplification in the neutron star merger.

  3. The air afterglow revisited

    NASA Technical Reports Server (NTRS)

    Kaufman, F.

    1972-01-01

    The air afterglow, 0 + NO2 chemiluminescence, is discussed in terms of fluorescence, photodissociation, and quantum theoretical calculations of NO2. The experimental results presented include pressure dependence, M-dependence, spectral dependence of P and M, temperature dependence, and infrared measurements. The NO2 energy transfer model is also discussed.

  4. Gamma-Ray Burst Afterglow Broadband Fitting Based Directly on Hydrodynamics Simulations

    NASA Astrophysics Data System (ADS)

    van Eerten, Hendrik; van der Horst, Alexander; MacFadyen, Andrew

    2012-04-01

    We present a powerful new tool for fitting broadband gamma-ray burst afterglow data, which can be used to determine the burst explosion parameters and the synchrotron radiation parameters. By making use of scale invariance between relativistic jets of different energies and different circumburst medium densities, and by capturing the output of high-resolution two-dimensional relativistic hydrodynamical (RHD) jet simulations in a concise summary, the jet dynamics are generated quickly. Our method calculates the full light curves and spectra using linear radiative transfer sufficiently fast to allow for a direct iterative fit of RHD simulations to the data. The fit properly accounts for jet features that so far have not been successfully modeled analytically, such as jet decollimation, inhomogeneity along the shock front, and the transitory phase between the early-time relativistic and late-time non-relativistic outflow. As a first application of the model we simultaneously fit the radio, X-ray, and optical data of GRB 990510. We find not only noticeable differences between our findings for the explosion and radiation parameters and those of earlier authors, but also an improved model fit when we include the observer angle in the data fit. The fit method will be made freely available on request and online at http://cosmo.nyu.edu/afterglowlibrary. In addition to data fitting, the software tools can also be used to quickly generate a light curve or spectrum for arbitrary observer position, jet, and radiation parameters.

  5. The 'Supercritical Pile' GRB Model: Afterglows and GRB, XRR, XRF Unification

    NASA Technical Reports Server (NTRS)

    Kazanas, D.

    2007-01-01

    We present the general notions and observational consequences of the "Supercritical Pile" GRB model; the fundamental feature of this model is a detailed process for the conversion of the energy stored in relativistic protons in the GRB Relativistic Blast Waves (RBW) into relativistic electrons and then into radiation. The conversion is effected through the $p \\, \\gamma \\rightarrow p \\, e circumflex + e circumflex -$ reaction, whose kinematic threshold is imprinted on the GRB spectra to provide a peak of their emitted luminosity at energy \\Ep $\\sim 1$ MeV in the lab frame. We extend this model to include, in addition to the (quasi--)thermal relativistic post-shock protons an accelerated component of power law form. This component guarantees the production of $e circumflex +e circumflex- - $pairs even after the RBW has slowed down to the point that its (quasi-) thermal protons cannot fulfill the threshold of the above reaction. We suggest that this last condition marks the transition from the prompt to the afterglow GRB phase. We also discuss conditions under which this transition is accompanied by a significant drop in the flux and could thus account for several puzzling, recent observations. Finally, we indicate that the same mechanism applied to the late stages of the GRB evolution leads to a decrease in \\Ep $\\propto \\Gamma circumflex 2(t)\\propto t circumflex {-3/4}$, a feature amenable to future observational tests.

  6. The Energy Budget of GRBs Based on a Large Sample of Prompt and Afterglow Observations

    NASA Astrophysics Data System (ADS)

    Wygoda, N.; Guetta, D.; Mandich, M. A.; Waxman, E.

    2016-06-01

    We compare the isotropic equivalent 15-2000 keV γ-ray energy, E γ , emitted by a sample of 91 swift Gamma-Ray Bursts with known redshifts, with the isotropic equivalent fireball energy, E fb, as estimated within the fireball model framework from X-ray afterglow observations of these bursts. The uncertainty in E γ , which spans the range of ˜1051 to ˜1053.5 erg, is ≈25% on average, due mainly to the extrapolation from the BAT detector band to the 15-2000 keV band. The uncertainty in E fb is approximately a factor of 2, due mainly to the X-ray measurements’ scatter. We find E γ and E fb to be tightly correlated. The average(std) of {η }γ 11 {hr}\\equiv {{log}}10({E}γ /(3{\\varepsilon }{{e}}{E}{{fb}}11 {hr})) are -0.34(0.60), and the upper limit on the intrinsic spread of η γ is approximately 0.5 ({\\varepsilon }{{e}} is the fraction of energy carried by electrons and {E}{{fb}}x {hr} is inferred from the X-ray flux at x hours). {E}{{fb}}3 {hr} and {E}{{fb}}11 {hr} are similar, with an average(std) of {{log}}10({E}{{fb}}3 {hr}/{E}{{fb}}11 {hr}) of 0.04(0.28). The small variance of η γ implies that burst-to-burst variations in {\\varepsilon }{{e}} and in the efficiency of fireball energy conversion to γ-rays are small, and suggests that both are of order unity. The small variance of η γ and the similarity of {E}{{fb}}3 {hr} and {E}{{fb}}11 {hr} further imply that deviations from a simple fireball model description, if present, are small. This puts stringent constraints on models incorporating such modifications (due e.g., to radiative losses, energy injection, off-axis viewing).

  7. The Energy Budget of GRBs Based on a Large Sample of Prompt and Afterglow Observations

    NASA Astrophysics Data System (ADS)

    Wygoda, N.; Guetta, D.; Mandich, M. A.; Waxman, E.

    2016-06-01

    We compare the isotropic equivalent 15–2000 keV γ-ray energy, E γ , emitted by a sample of 91 swift Gamma-Ray Bursts with known redshifts, with the isotropic equivalent fireball energy, E fb, as estimated within the fireball model framework from X-ray afterglow observations of these bursts. The uncertainty in E γ , which spans the range of ˜1051 to ˜1053.5 erg, is ≈25% on average, due mainly to the extrapolation from the BAT detector band to the 15–2000 keV band. The uncertainty in E fb is approximately a factor of 2, due mainly to the X-ray measurements’ scatter. We find E γ and E fb to be tightly correlated. The average(std) of {η }γ 11 {hr}\\equiv {{log}}10({E}γ /(3{\\varepsilon }{{e}}{E}{{fb}}11 {hr})) are ‑0.34(0.60), and the upper limit on the intrinsic spread of η γ is approximately 0.5 ({\\varepsilon }{{e}} is the fraction of energy carried by electrons and {E}{{fb}}x {hr} is inferred from the X-ray flux at x hours). {E}{{fb}}3 {hr} and {E}{{fb}}11 {hr} are similar, with an average(std) of {{log}}10({E}{{fb}}3 {hr}/{E}{{fb}}11 {hr}) of 0.04(0.28). The small variance of η γ implies that burst-to-burst variations in {\\varepsilon }{{e}} and in the efficiency of fireball energy conversion to γ-rays are small, and suggests that both are of order unity. The small variance of η γ and the similarity of {E}{{fb}}3 {hr} and {E}{{fb}}11 {hr} further imply that deviations from a simple fireball model description, if present, are small. This puts stringent constraints on models incorporating such modifications (due e.g., to radiative losses, energy injection, off-axis viewing).

  8. The Onset of Gamma-Ray Burst Afterglow

    NASA Astrophysics Data System (ADS)

    Kobayashi, Shiho; Zhang, Bing

    2007-02-01

    We discuss the reference time t0 of afterglow light curves in the context of the standard internal-external shock model. The decay index of early afterglow is very sensitive to the reference time one chooses. In order to understand the nature of early afterglow, it is essential to take a correct reference time. Our simple analytic model provides a framework for understanding special relativistic effects involved in early afterglow phase. We evaluate light curves of reverse shock emission as well as those of forward shock emission, based on full hydrodynamic calculations. We show that the reference time does not shift significantly even in the thick-shell case. For external shock emission components, measuring times from the beginning of the prompt emission is a good approximation and it does not cause an early steep decay. In the thin-shell case, the energy transfer time from fireball ejecta to ambient medium typically extends to thousands of seconds. This might be related to the shallow decay phases observed in early X-ray afterglow at least for some bursts.

  9. Influence of plasma diffusion losses on dust charge relaxation in discharge afterglow

    SciTech Connect

    Coueedel, L.; Mikikian, M.; Boufendi, L.

    2008-09-07

    The influence of diffusive losses on residual dust charge in a complex plasma afterglow has been investigated. The dust residual charges were simulated based on a model developed to describe complex plasma decay. The experimental and simulated data show that the transition from ambipolar to free diffusion in the decaying plasma plays a significant role in determining the residual dust particle charges. The presence of positively charged dust particles is explained by a broadening of the charge distribution function in the afterglow plasma.

  10. Modeling the Multi-band Afterglow of GRB 130831A: Evidence for a Spinning-down Magnetar Dominated by Gravitational Wave Losses?

    NASA Astrophysics Data System (ADS)

    Zhang, Q.; Huang, Y. F.; Zong, H. S.

    2016-06-01

    The X-ray afterglow of GRB 130831A shows an “internal plateau” with a decay slope of ˜0.8, followed by a steep drop at around 105 s with a slope of ˜6. After the drop, the X-ray afterglow continues with a much shallower decay. The optical afterglow exhibits two segments of plateaus separated by a luminous optical flare, followed by a normal decay with a slope basically consistent with that of the late-time X-ray afterglow. The decay of the internal X-ray plateau is much steeper than what we expect in the simplest magnetar model. We propose a scenario in which the magnetar undergoes gravitational-wave-driven r-mode instability, and the spin-down is dominated by gravitational wave losses up to the end of the steep plateau, so that such a relatively steep plateau can be interpreted as the internal emission of the magnetar wind and the sharp drop can be produced when the magnetar collapses into a black hole. This scenario also predicts an initial X-ray plateau lasting for hundreds of seconds with an approximately constant flux which is compatible with observation. Assuming that the magnetar wind has a negligible contribution in the optical band, we interpret the optical afterglow as the forward shock emission by invoking the energy injection from a continuously refreshed shock following the prompt emission phase. It is shown that our model can basically describe the temporal evolution of the multi-band afterglow of GRB 130831A.

  11. GLAST Prospects for Swift-Era Afterglows

    SciTech Connect

    Gou, L.J.; Meszaros, P.; /Penn State U.

    2011-11-23

    We calculate the GeV spectra of gamma-ray burst afterglows produced by inverse Compton scattering of these objects sub-MeV emission. We improve on earlier treatments by using refined afterglow parameters and new model developments motivated by recent Swift observations. We present time-dependent GeV spectra for standard, constant-parameter models, as well as for models with energy injection and with time-varying parameters, for a range of burst parameters. We evaluate the limiting redshift to which such afterglows can be detected by the GLAST Large Area Telescope, as well as by AGILE.

  12. Dust Cloud Dynamics in Complex Plasma Afterglow

    SciTech Connect

    Layden, B.; Samarian, A. A.; Vladimirov, S. V.; Coueedel, L.

    2008-09-07

    Experimental observations of dust cloud dynamics in a RF discharge afterglow are presented. Image analysis is used to extract information from videos taken of the plasma. Estimations of the mean confining electric field have been made for different experimental conditions using a model for the contraction of the dust cloud. Dust particle trajectories in the late afterglow evidence the co-existence of positively and negatively charged dust particles.

  13. Afterglow Radiation from Gamma Ray Bursts

    SciTech Connect

    Desmond, Hugh; /Leuven U. /SLAC

    2006-08-28

    Gamma-ray bursts (GRB) are huge fluxes of gamma rays that appear randomly in the sky about once a day. It is now commonly accepted that GRBs are caused by a stellar object shooting off a powerful plasma jet along its rotation axis. After the initial outburst of gamma rays, a lower intensity radiation remains, called the afterglow. Using the data from a hydrodynamical numerical simulation that models the dynamics of the jet, we calculated the expected light curve of the afterglow radiation that would be observed on earth. We calculated the light curve and spectrum and compared them to the light curves and spectra predicted by two analytical models of the expansion of the jet (which are based on the Blandford and McKee solution of a relativistic isotropic expansion; see Sari's model [1] and Granot's model [2]). We found that the light curve did not decay as fast as predicted by Sari; the predictions by Granot were largely corroborated. Some results, however, did not match Granot's predictions, and more research is needed to explain these discrepancies.

  14. DIVERSITY OF SHORT GAMMA-RAY BURST AFTERGLOWS FROM COMPACT BINARY MERGERS HOSTING PULSARS

    SciTech Connect

    Holcomb, Cole; Ramirez-Ruiz, Enrico; De Colle, Fabio; Montes, Gabriela

    2014-07-20

    Short-duration gamma-ray bursts (sGRBs) are widely believed to result from the mergers of compact binaries. This model predicts an afterglow that bears the characteristic signatures of a constant, low-density medium, including a smooth prompt-afterglow transition, and a simple temporal evolution. However, these expectations are in conflict with observations for a non-negligible fraction of sGRB afterglows. In particular, the onset of the afterglow phase for some of these events appears to be delayed and, in addition, a few of them exhibit late-time rapid fading in their light curves. We show that these peculiar observations can be explained independently of ongoing central engine activity if some sGRB progenitors are compact binaries hosting at least one pulsar. The Poynting flux emanating from the pulsar companion can excavate a bow-shock cavity surrounding the binary. If this cavity is larger than the shock deceleration length scale in the undisturbed interstellar medium, then the onset of the afterglow will be delayed. Should the deceleration occur entirely within the swept-up thin shell, a rapid fade in the light curve will ensue. We identify two types of pulsar that can achieve the conditions necessary for altering the afterglow: low-field, long-lived pulsars, and high-field pulsars. We find that a sizable fraction (≈20%-50%) of low-field pulsars are likely to reside in neutron star binaries based on observations, while their high-field counterparts are not. Hydrodynamical calculations motivated by this model are shown to be in good agreement with observations of sGRB afterglow light curves.

  15. X-ray plateaus in the context of the one-zone SSC model for GRB afterglows

    SciTech Connect

    Petropoulou, M.; Mastichiadis, A.

    2010-10-15

    We investigate the impact that the upper cutoff of the electron distribution has on the multiwavelength GRB afterglow spectra and on the corresponding X-ray light curves. We show under which conditions X-ray light curves with a plateau phase can be produced in this picture.

  16. The ultra-long GRB 111209A. II. Prompt to afterglow and afterglow properties

    SciTech Connect

    Stratta, G.; Gendre, B.; Boër, M.; Atteia, J. L.; Coward, D. M.; Howell, E.; De Pasquale, M.; Oates, S.; Klotz, A.; Piro, L.

    2013-12-10

    The 'ultra-long' gamma-ray burst GRB 111209A at redshift z = 0.677 is the longest GRB ever observed thus far, with a rest frame prompt emission duration of ∼4 hr. In order to explain the burst exceptional longevity, a low-metallicity blue supergiant progenitor was invoked. In this article we further constrain the phenomenology and progenitor properties of this peculiar GRB by performing a multiband 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, and 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: (1) an unprecedented large optical delay of 410 ± 50 s between the peak time in gamma-rays and the peak time in the optical of a marked multiwavelength flare; (2) multiwavelength prompt emission spectral modeling requires a certain amount of dust in the circumburst environment. The dust produces a rest frame visual extinction of A{sub V} = 0.3-1.5 mag, and may undergo destruction at late times; and (3) we detect the presence of a hard spectral extra power-law component at the end of the X-ray steep steep decay phase and before the start of the X-ray afterglow, which has never been revealed thus far in past GRBs. The optical afterglow shows more usual properties; it has a flux power-law decay with an index of 1.6 ± 0.1 and a late rebrightening feature observed at ∼1.1 the day after the first Burst Alert Telescope trigger. We discuss our findings in the context of several possible interpretations that have been given thus far of the complex multiband GRB phenomenology and propose a binary channel formation for the blue supergiant progenitor.

  17. Comparison of Three Afterglow Morphologies

    SciTech Connect

    Salmonson, J D; Rossi, E; Lazzati, D

    2003-12-23

    Herein we compare three functional families for afterglow morphologies: the homogeneous afterglow with constant shock surface energy density, the structured afterglow for which the energy density decays as a power-law as a function of viewer angle, and the gaussian afterglow which has an exponential decay of energy density with viewer angle. We simulate observed lightcurves and polarization curves for each as seen from a variety of observer vantage points. We find that the homogeneous jet is likely inconsistent with observations and suggest that the future debate on the structure of afterglow jets will be between the other two candidates.

  18. SPIN EVOLUTION OF MILLISECOND MAGNETARS WITH HYPERACCRETING FALLBACK DISKS: IMPLICATIONS FOR EARLY AFTERGLOWS OF GAMMA-RAY BURSTS

    SciTech Connect

    Dai, Z. G.; Liu Ruoyu E-mail: ryliu@nju.edu.cn

    2012-11-01

    The shallow decay phase or plateau phase of early afterglows of gamma-ray bursts (GRBs), discovered by Swift, is currently understood as being due to energy injection to a relativistic blast wave. One natural scenario for energy injection invokes a millisecond magnetar as the central engine of GRBs because the conventional model of a pulsar predicts a nearly constant magnetic-dipole-radiation luminosity within the spin-down timescale. However, we note that significant brightening occurs in some early afterglows, which apparently conflicts with the above scenario. Here we propose a new model to explain this significant brightening phenomena by considering a hyperaccreting fallback disk around a newborn millisecond magnetar. We show that for typical values of the model parameters, sufficient angular momentum of the accreted matter is transferred to the magnetar and spins it up. It is this spin-up that leads to a dramatic increase of the magnetic-dipole-radiation luminosity with time and thus significant brightening of an early afterglow. Based on this model, we carry out numerical calculations and fit well early afterglows of 12 GRBs assuming sufficiently strong fallback accretion. If the accretion is very weak, our model turns out to be the conventional energy-injection scenario of a pulsar. Therefore, our model can provide a unified explanation for the shallow decay phase, plateaus, and significant brightening of early afterglows.

  19. rf-generated ambient-afterglow plasma

    SciTech Connect

    Shakir, Shariff; Mynampati, Sandhya; Pashaie, Bijan; Dhali, Shirshak K.

    2006-04-01

    Atmospheric pressure plasmas have gained importance due to their potential application in polymer surface treatment, surface cleaning of metals, thin film deposition, and destruction of biological hazards. In this paper a radio-frequency driven atmospheric pressure afterglow plasma source in argon and helium is discussed. The light intensity measurement shows that the radio-frequency discharge is continuous in time unlike the intermittent nature of a low frequency dielectric-barrier discharge. The discharge, under ambient conditions, can be generated in argon, helium, and nitrogen. Spectroscopic measurements show that metastables are capable of producing oxygen atoms and other excited species. The argon afterglow, in particular, is capable of dissociating oxygen molecules in the ambient gas. An afterglow model has been developed to study the interaction of the plasma with the ambient gas. Results from applications of the plasma to surface treatment of metals and polymers, and bacterial decontamination are briefly discussed.

  20. Simulation Study Of Early Afterglows Observed With Swift

    NASA Astrophysics Data System (ADS)

    Nishikawa, Ken-Ichi; Hededal, C.; Hardee, P.; Mizuno, Y.; Fishman, G. J.

    2006-09-01

    A 3-D relativistic particle-in-cell code has been used to simulate the dynamics of forward and reverse shocks with thin and thick shells within the parameter constraints provided by present Swift observations and the present models of GRB emission. Our 3-D RPIC simulations have provided the dynamics of collisionless shocks in electron-ion and electron-positron plasmas with and without initial ambient magnetic fields and revealed the importance of ``jitter radiation'' with prompt and afterglow spectra due to the inhomogeneous magnetic fields generated by the Weibel instability. It is different from synchrotron radiation, which is usually assumed to be the dominant radiation process. We have investigated gamma-ray burst emissions from prompt, early, and late afterglows considering microscopic processes. Based on our previous investigation of the Weibel instability for each stage of evolution of ejecta propagating in the ISM, we have incorporated the plasma conditions (relativistic jets) with the density and composition of the plasmas, the magnetic field strength ($\\sigma$-values (the ratio of the electromagnetic energy flux to the particle energy flux)) and its direction, and the Lorentz factor for the different stages in prompt and afterglows. Systematic simulation studies of the relativistic collisionless shocks, associated particle acceleration, magnetic field generation and self-consistent radiation provide insight into undetermined issues in prompt and afterglows observed by Swift. Self-consistently calculated lightcurves, spectra, spectral evolutions, and polarization as function of viewing angle will be done to light a shed on recent new observations by Swift, in particular, X-ray flares, early steep decay, and shallow decay.

  1. Observation on long afterglow of Tb{sup 3+} in CaWO{sub 4}

    SciTech Connect

    Wu, Haoyi; Hu, Yihua; Kang, Fengwen; Chen, Li; Wang, Xiaojuan; Ju, Guifang; Mu, Zhongfei

    2011-12-15

    Graphical abstract: The afterglow of Tb{sup 3+} is observed in CaWO{sub 4} matrix. The main emission of the afterglow is ascribed to the {sup 5}D{sub 4} {yields} {sup 7}F{sub 5} and {sup 5}D{sub 4} {yields} {sup 7}F{sub 6}. Emission due to {sup 5}D{sub 3} {yields} {sup 7}F{sub 4} and {sup 5}D{sub 3} {yields} {sup 7}F{sub 5} is weak. The cross-relaxation dominate the afterglow emission and it enhances the transition from {sup 5}D{sub 4} whereas from {sup 5}D{sub 3}. Highlights: Black-Right-Pointing-Pointer A green long afterglow is observed from Tb{sup 3+} in CaWO{sub 4} matrix. Black-Right-Pointing-Pointer Two traps which may have a strong influence on the afterglow properties are revealed by TL. Black-Right-Pointing-Pointer A mechanism model based on energy transfer from WO{sub 4}{sup 2-} group to Tb{sup 3+} followed by cross-relaxation is proposed. -- Abstract: The Tb{sup 3+} doped CaWO{sub 4} phosphors are synthesized via high temperature solid state reaction. The X-ray diffraction shows that small amount of Tb{sup 3+} does not have a significant influence on the structure of CaWO{sub 4}. A broad absorption band of the WO{sub 4}{sup 2-} group is observed from photoluminescence and the energy transfer from WO{sub 4}{sup 2-} group to Tb{sup 3+} ions induces the f-f transition. The cross-relaxation between two adjacent Tb{sup 3+} ions weakens {sup 5}D{sub 3}-{sup 7}F{sub j} transitions and enhances the {sup 5}D{sub 4}-{sup 7}F{sub j} transitions, leading to a green long afterglow of the phosphors. The thermoluminescence curves centered around 75 Degree-Sign C reveal the trap depth for afterglow generation is about 0.74-0.77 eV. The optimum Tb{sup 3+} concentration for afterglow properties is about 1%. A deep hole trap is induced when Tb{sup 3+} concentration exceeds 1% and it suppresses the thermoluminescence and the decay properties.

  2. GRB 110530A: Peculiar Broad Bump and Delayed Plateau in Early Optical Afterglows

    NASA Astrophysics Data System (ADS)

    Zhong, Shu-Qing; Xin, Li-Ping; Liang, En-Wei; Wei, Jian-Yan; Urata, Yuji; Huang, Kui-Yun; Qiu, Yu-Lei; Deng, Can-Min; Wang, Yuan-Zhu; Deng, Jin-Song

    2016-11-01

    We report our very early optical observations of GRB 110530A and investigate its jet properties together with its X-ray afterglow data. A peculiar broad onset bump followed by a plateau is observed in its early R band afterglow light curve. The optical data in the other bands and the X-ray data are well consistent with the temporal feature of the R band light curve. Our joint spectral fits of the optical and X-ray data show that they are in the same regime, with a photon index of ∼1.70. The optical and X-ray afterglow light curves are well fitted with the standard external shock model by considering a delayed energy injection component. Based on our modeling results, we find that the radiative efficiency of the gamma-ray burst jet is ∼ 1 % and the magnetization parameter of the afterglow jet is \\lt 0.04 with a derived extremely low {ε }B (the ratio of shock energy to the magnetic field) of (1.64+/- 0.25)× {10}-6. These results indicate that the jet may be matter dominated. A discussion on delayed energy injection from the accretion of the late fall-back material of its pre-supernova star is also presented.

  3. The Detectability of Orphan Afterglows

    NASA Astrophysics Data System (ADS)

    Nakar, Ehud; Piran, Tsvi; Granot, Jonathan

    2002-11-01

    The realization that gamma-ray bursts (GRBs) release a constant amount of energy implies that post-jet-break afterglow evolution is largely universal. For a given redshift, all afterglows should be detected up to a fixed observer angle. We estimate the observed magnitude and the implied detectability of orphan afterglows. We show that for reasonable limiting magnitudes (mlim=25), orphan afterglows will typically be detected from small (~10°) angles away from the GRB jet axis. A detected orphan afterglow generally corresponds to a ``near miss'' of a GRB whose jet is pointing just slightly away from us. With our most optimistic parameters, we expect that 15 orphan afterglows will be recorded in the Sloan Digital Sky Survey, and 35 transients will be recorded in a dedicated 2 m class telescope operating full time for a year in an orphan afterglow search. The rate is smaller by a factor of 15 for our ``canonical'' parameters. We show that for a given facility, an optimal survey should be shallower, covering a larger area, rather than deeper. The limiting magnitude should not be, however, lower than ~23, as in this case, more transients from on-axis GRBs will be discovered than orphan afterglows. About 15% of the transients could be discovered with a second exposure of the same area provided that it follows after 3, 4, and 8 days for mlim=23, 25, and 27, respectively.

  4. Linear and circular polarimetry observations of gamma-ray burst afterglows

    NASA Astrophysics Data System (ADS)

    Wiersema, K.

    2013-07-01

    Follow-up observations of large numbers of gamma-ray burst (GRB) afterglows, facilitated by the Swift satellite, have produced a large sample of spectral energy distributions and light curves, from which the basic micro- and macrophysical parameters of afterglows may be derived. However, a number of phenomena have been observed that defy explanation by simple versions of the standard fireball model, leading to a variety of new models. Polarimetry has shown great promise as a diagnosis of afterglow physics, probing the magnetic field properties of the afterglow and geometrical effects (e.g. jet breaks). Unfortunately, high quality polarimetry of a significant sample of afterglows is difficult to acquire, requiring specialised instrumentation and observing modes. In this talk I will review the recent successes in afterglow polarimetry, also showing first results of new instruments and observing campaigns. I will particularly focus on jet breaks.

  5. Study of argon-oxygen flowing afterglow

    NASA Astrophysics Data System (ADS)

    Mazánková, V.; Trunec, D.; Navrátil, Z.; Raud, J.; Krčma, F.

    2016-06-01

    The reaction kinetics in argon-oxygen flowing afterglow (post-discharge) was studied using NO titration and optical emission spectroscopy. The flowing DC post-discharge in argon-oxygen mixture was created in a quartz tube at the total gas pressure of 1000 Pa and discharge power of 90 W. The O(3P) atom concentration was determined by NO titration at different places along the flow tube. The optical emission spectra were also measured along the flow tube. Argon spectral lines, oxygen lines at 777 nm and 844.6 nm and atmospheric A-band of {{\\text{O}}2} were identified in the spectra. Rotational temperature of {{\\text{O}}2} was determined from the oxygen atmospheric A-band and also the outer wall temperature of the flow tube was measured by a thermocouple and by an IR thermometer. A zero-dimensional kinetic model for the reactions in the afterglow was developed. This model allows the time dependencies of particle concentrations and of gas temperature to be calculated. The wall recombination probability for O(3P) atoms {γ\\text{O≤ft(\\text{P}\\right)}}=≤ft(1.63+/- 0.06\\right)× {{10}-3} and wall deactivation probability for {{\\text{O}}2} (b {{}1}Σ\\text{g}+ ) molecules {γ{{\\text{O}2}≤ft(\\text{b}\\right)}}=≤ft(1.7+/- 0.1\\right)× {{10}-3} were determined from the fit of model results to experimental data. Sensitivity analysis was applied for the analysis of kinetic model in order to reveal the most important reactions in the model. The calculated gas temperature increases in the afterglow and then decreases at later afterglow times after reaching the maximum. This behavior is in good agreement with the spatial rotational temperature dependence. A similar trend was also observed at outer wall temperature measurement.

  6. Study of argon–oxygen flowing afterglow

    NASA Astrophysics Data System (ADS)

    Mazánková, V.; Trunec, D.; Navrátil, Z.; Raud, J.; Krčma, F.

    2016-06-01

    The reaction kinetics in argon–oxygen flowing afterglow (post-discharge) was studied using NO titration and optical emission spectroscopy. The flowing DC post-discharge in argon–oxygen mixture was created in a quartz tube at the total gas pressure of 1000 Pa and discharge power of 90 W. The O(3P) atom concentration was determined by NO titration at different places along the flow tube. The optical emission spectra were also measured along the flow tube. Argon spectral lines, oxygen lines at 777 nm and 844.6 nm and atmospheric A-band of {{\\text{O}}2} were identified in the spectra. Rotational temperature of {{\\text{O}}2} was determined from the oxygen atmospheric A-band and also the outer wall temperature of the flow tube was measured by a thermocouple and by an IR thermometer. A zero-dimensional kinetic model for the reactions in the afterglow was developed. This model allows the time dependencies of particle concentrations and of gas temperature to be calculated. The wall recombination probability for O(3P) atoms {γ\\text{O≤ft(\\text{P}\\right)}}=≤ft(1.63+/- 0.06\\right)× {{10}-3} and wall deactivation probability for {{\\text{O}}2} (b {{}1}Σ\\text{g}+ ) molecules {γ{{\\text{O}2}≤ft(\\text{b}\\right)}}=≤ft(1.7+/- 0.1\\right)× {{10}-3} were determined from the fit of model results to experimental data. Sensitivity analysis was applied for the analysis of kinetic model in order to reveal the most important reactions in the model. The calculated gas temperature increases in the afterglow and then decreases at later afterglow times after reaching the maximum. This behavior is in good agreement with the spatial rotational temperature dependence. A similar trend was also observed at outer wall temperature measurement.

  7. The 80 Ms follow-up of the X-ray afterglow of GRB 130427A challenges the standard forward shock model

    NASA Astrophysics Data System (ADS)

    De Pasquale, M.; Page, M. J.; Kann, D. A.; Oates, S. R.; Schulze, S.; Zhang, B.; Cano, Z.; Gendre, B.; Malesani, D.; Rossi, A.; Troja, E.; Piro, L.; Boër, M.; Stratta, G.; Gehrels, N.

    2016-10-01

    GRB 130427A was the brightest gamma-ray burst detected in the last 30 yr. With an equivalent isotropic energy output of 8.5 × 1053 erg and redshift z = 0.34, it uniquely combined very high energetics with a relative proximity to Earth. As a consequence, its X-ray afterglow has been detected by sensitive X-ray observatories such as XMM-Newton and Chandra for a record-breaking baseline longer than 80 million seconds. We present the X-ray light curve of this event over such an interval. The light curve shows a simple power-law decay with a slope α = 1.309 ± 0.007 over more than three decades in time (47 ks-83 Ms). We discuss the consequences of this result for a few models proposed so far to interpret GRB 130427A, and more in general the significance of this outcome in the context of the standard forward shock model. We find that this model has difficulty in explaining our data, in both cases of constant density and stellar-wind circumburst media, and requires far-fetched values for the physical parameters involved.

  8. Afterglow chemistry of atmospheric-pressure helium-oxygen plasmas with humid air impurity

    NASA Astrophysics Data System (ADS)

    Murakami, Tomoyuki; Niemi, Kari; Gans, Timo; O'Connell, Deborah; Graham, William G.

    2014-04-01

    The formation of reactive species in the afterglow of a radio-frequency-driven atmospheric-pressure plasma in a fixed helium-oxygen feed gas mixture (He+0.5%O2) with humid air impurity (a few hundred ppm) is investigated by means of an extensive global plasma chemical kinetics model. As an original objective, we explore the effects of humid air impurity on the biologically relevant reactive species in an oxygen-dependent system. After a few milliseconds in the afterglow environment, the densities of atomic oxygen (O) decreases from 1015 to 1013 cm-3 and singlet delta molecular oxygen (O2(1D)) of the order of 1015 cm-3 decreases by a factor of two, while the ozone (O3) density increases from 1014 to 1015 cm-3. Electrons and oxygen ionic species, initially of the order of 1011 cm-3, recombine much faster on the time scale of some microseconds. The formation of atomic hydrogen (H), hydroxyl radical (OH), hydroperoxyl (HO2), hydrogen peroxide (H2O2), nitric oxide (NO) and nitric acid (HNO3) resulting from the humid air impurity as well as the influence on the afterglow chemistry is clarified with particular emphasis on the formation of dominant reactive oxygen species (ROS). The model suggests that the reactive species predominantly formed in the afterglow are major ROS O2(1D) and O3 (of the order of 1015 cm-3) and rather minor hydrogen- and nitrogen-based reactive species OH, H2O2, HNO3 and NO2/NO3, of which densities are comparable to the O-atom density (of the order of 1013 cm-3). Furthermore, the model quantitatively reproduces the experimental results of independent O and O3 density measurements.

  9. GRB 030329: 3 years of radio afterglow monitoring.

    PubMed

    van der Horst, A J; Kamble, A; Wijers, R A M J; Resmi, L; Bhattacharya, D; Rol, E; Strom, R; Kouveliotou, C; Oosterloo, T; Ishwara-Chandra, C H

    2007-05-15

    Radio observations of gamma-ray burst (GRB) afterglows are essential for our understanding of the physics of relativistic blast waves, as they enable us to follow the evolution of GRB explosions much longer than the afterglows in any other wave band. We have performed a 3-year monitoring campaign of GRB 030329 with the Westerbork Synthesis Radio Telescopes and the Giant Metrewave Radio Telescope. Our observations, combined with observations at other wavelengths, have allowed us to determine the GRB blast wave physical parameters, such as the total burst energy and the ambient medium density, as well as to investigate the jet nature of the relativistic outflow. Further, by modelling the late-time radio light curve of GRB 030329, we predict that the Low-Frequency Array (30-240 MHz) will be able to observe afterglows of similar GRBs, and constrain the physics of the blast wave during its non-relativistic phase.

  10. GRB 030329: 3 years of radio afterglow monitoring.

    PubMed

    van der Horst, A J; Kamble, A; Wijers, R A M J; Resmi, L; Bhattacharya, D; Rol, E; Strom, R; Kouveliotou, C; Oosterloo, T; Ishwara-Chandra, C H

    2007-05-15

    Radio observations of gamma-ray burst (GRB) afterglows are essential for our understanding of the physics of relativistic blast waves, as they enable us to follow the evolution of GRB explosions much longer than the afterglows in any other wave band. We have performed a 3-year monitoring campaign of GRB 030329 with the Westerbork Synthesis Radio Telescopes and the Giant Metrewave Radio Telescope. Our observations, combined with observations at other wavelengths, have allowed us to determine the GRB blast wave physical parameters, such as the total burst energy and the ambient medium density, as well as to investigate the jet nature of the relativistic outflow. Further, by modelling the late-time radio light curve of GRB 030329, we predict that the Low-Frequency Array (30-240 MHz) will be able to observe afterglows of similar GRBs, and constrain the physics of the blast wave during its non-relativistic phase. PMID:17293318

  11. GRB 081029: A Gamma-Ray Burst with a Multi-Component Afterglow

    NASA Technical Reports Server (NTRS)

    Holland, Stephen T.; DePasquale, Massimiliano; Mao, Jirong; Sakamoto, Taka; Shady, Patricia; Covino, Stefano; Yi-Zhong, Fan; Zhi-Ping, Jin; D'Avanzo, Paolo; Antonelli, Angelo; D'Elia, Valerio; Chincarini, Guido; Fiore, Fabrizio; Pandey, Shashi Bhushan

    2011-01-01

    We present an analysis of the unusual optical light curve of the gamma-ray burst GRB 081029, a long-soft burst with a redshift of z = 3.8479. We combine X-ray and optical observations from the Swift X-Ray Telescope and the Swift UltraViolet Optical Telescope with ground-based optical and infrared data obtained using the REM and ROTSE telescopes to construct a detailed data set extending from 86 s to approx. 100000 s after the BAT trigger. Our data cover a wide energy range, from 10 keV to 0.77 eV (1.24 A to 16000 A). The X-ray afterglow shows a shallow initial decay followed by a rapid decay starting at about 18000 s. The optical and infrared afterglow, however, shows an uncharacteristic rise at about 5000 s that does not correspond to any feature in the X-ray light curve. Our data are not consistent with synchrotron radiation from a jet interacting with an external medium, a two-component jet, or continuous energy injection from the central engine. We find that the the optical light curves can be broadly explained by a collision between two ejecta shells within a two-component jet. A growing number of gamma-ray burst afterglows are consistent with complex jets, which suggests that some (or all) gamma-ray burst jets are complex and will require detailed modelling to fully understand them.

  12. GRB 081029: A GAMMA-RAY BURST WITH A MULTI-COMPONENT AFTERGLOW

    SciTech Connect

    Holland, Stephen T.; Sakamoto, Takanori; De Pasquale, Massimiliano; Schady, Patricia; Mao, Jirong; Covino, Stefano; Jin, Zhi-Ping; D'Avanzo, Paolo; Chincarini, Guido; Fan, Yi-Zhong; Antonelli, Angelo; D'Elia, Valerio; Fiore, Fabrizio; Pandey, Shashi Bhushan; Cobb, Bethany E.

    2012-01-20

    We present an analysis of the unusual optical light curve of the gamma-ray burst GRB 081029, a long-soft burst with a redshift of z = 3.8479. We combine X-ray and optical observations from the Swift X-Ray Telescope and the Swift UltraViolet/Optical Telescope with ground-based optical and infrared data obtained using the REM, ROTSE, and CTIO 1.3 m telescopes to construct a detailed data set extending from 86 s to {approx}100000 s after the BAT trigger. Our data cover a wide energy range from 10 keV to 0.77 eV (1.24 A-16000 A). The X-ray afterglow shows a shallow initial decay followed by a rapid decay starting at about 18000 s. The optical and infrared afterglow, however, shows an uncharacteristic rise at about 3000 s that does not correspond to any feature in the X-ray light curve. Our data are not consistent with synchrotron radiation from a jet interacting with an external medium, a two-component jet, or continuous energy injection from the central engine. We find that the optical light curves can be broadly explained by a collision between two ejecta shells within a two-component jet. A growing number of gamma-ray-burst afterglows are consistent with complex jets, which suggests that some (or all) gamma-ray-burst jets are complex and will require detailed modeling to fully understand them.

  13. On the optical and X-ray afterglows of gamma ray bursts

    NASA Astrophysics Data System (ADS)

    Dado, S.; Dar, A.; De Rújula, A.

    2002-06-01

    We severely criticize the consuetudinary analysis of the afterglows of gamma-ray bursts (GRBs) in the conical-ejection fireball scenarios. We argue that, instead, recent observations imply that the long-duration GRBs and their afterglows are produced by highly relativistic jets of cannonballs (CBs) emitted in supernova explosions. The CBs are heated by their collision with the supernova shell. The GRB is the boosted surface radiation the CBs emit as they reach the transparent outskirts of the shell. The exiting CBs further decelerate by sweeping up interstellar matter (ISM). The early X-ray afterglow is dominated by thermal bremsstrahlung from the cooling CBs, the optical afterglow by synchrotron radiation from the ISM electrons swept up by the CBs. We show that this model fits simply and remarkably well all the measured optical afterglows of the 15 GRBs with known redshift, including that of GRB 990123, for which unusually prompt data are available. We demonstrate that GRB 980425 was a normal GRB produced by SN1998bw, with standard X-ray and optical afterglows. We find that the very peculiar afterglow of GRB 970508 can be explained if its CBs encountered a significant jump in density as they moved through the ISM. The afterglows of the nearest 8 of the known-redshift GRBs show various degrees of evidence for an association with a supernova akin to SN1998bw. In all other cases such an association, even if present, would have been undetectable with the best current photometric sensitivities. This gives strong support to the proposition that most, maybe all, of the long-duration GRBs are associated with supernovae. Although our emphasis is on optical afterglows, we also provide an excellent description of X-ray afterglows. Figures \\ref{fig228} to \\ref{X1216} are only available in electronic form at http:/www.edpsciences.org

  14. Circular polarization in the optical afterglow of GRB 121024A.

    PubMed

    Wiersema, K; Covino, S; Toma, K; van der Horst, A J; Varela, K; Min, M; Greiner, J; Starling, R L C; Tanvir, N R; Wijers, R A M J; Campana, S; Curran, P A; Fan, Y; Fynbo, J P U; Gorosabel, J; Gomboc, A; Götz, D; Hjorth, J; Jin, Z P; Kobayashi, S; Kouveliotou, C; Mundell, C; O'Brien, P T; Pian, E; Rowlinson, A; Russell, D M; Salvaterra, R; di Serego Alighieri, S; Tagliaferri, G; Vergani, S D; Elliott, J; Fariña, C; Hartoog, O E; Karjalainen, R; Klose, S; Knust, F; Levan, A J; Schady, P; Sudilovsky, V; Willingale, R

    2014-05-01

    Gamma-ray bursts (GRBs) are most probably powered by collimated relativistic outflows (jets) from accreting black holes at cosmological distances. Bright afterglows are produced when the outflow collides with the ambient medium. Afterglow polarization directly probes the magnetic properties of the jet when measured minutes after the burst, and it probes the geometric properties of the jet and the ambient medium when measured hours to days after the burst. High values of optical polarization detected minutes after the burst of GRB 120308A indicate the presence of large-scale ordered magnetic fields originating from the central engine (the power source of the GRB). Theoretical models predict low degrees of linear polarization and no circular polarization at late times, when the energy in the original ejecta is quickly transferred to the ambient medium and propagates farther into the medium as a blast wave. Here we report the detection of circularly polarized light in the afterglow of GRB 121024A, measured 0.15 days after the burst. We show that the circular polarization is intrinsic to the afterglow and unlikely to be produced by dust scattering or plasma propagation effects. A possible explanation is to invoke anisotropic (rather than the commonly assumed isotropic) electron pitch-angle distributions, and we suggest that new models are required to produce the complex microphysics of realistic shocks in relativistic jets.

  15. Circular polarization in the optical afterglow of GRB 121024A

    NASA Astrophysics Data System (ADS)

    Wiersema, K.; Covino, S.; Toma, K.; van der Horst, A. J.; Varela, K.; Min, M.; Greiner, J.; Starling, R. L. C.; Tanvir, N. R.; Wijers, R. A. M. J.; Campana, S.; Curran, P. A.; Fan, Y.; Fynbo, J. P. U.; Gorosabel, J.; Gomboc, A.; Götz, D.; Hjorth, J.; Jin, Z. P.; Kobayashi, S.; Kouveliotou, C.; Mundell, C.; O'Brien, P. T.; Pian, E.; Rowlinson, A.; Russell, D. M.; Salvaterra, R.; di Serego Alighieri, S.; Tagliaferri, G.; Vergani, S. D.; Elliott, J.; Fariña, C.; Hartoog, O. E.; Karjalainen, R.; Klose, S.; Knust, F.; Levan, A. J.; Schady, P.; Sudilovsky, V.; Willingale, R.

    2014-05-01

    Gamma-ray bursts (GRBs) are most probably powered by collimated relativistic outflows (jets) from accreting black holes at cosmological distances. Bright afterglows are produced when the outflow collides with the ambient medium. Afterglow polarization directly probes the magnetic properties of the jet when measured minutes after the burst, and it probes the geometric properties of the jet and the ambient medium when measured hours to days after the burst. High values of optical polarization detected minutes after the burst of GRB 120308A indicate the presence of large-scale ordered magnetic fields originating from the central engine (the power source of the GRB). Theoretical models predict low degrees of linear polarization and no circular polarization at late times, when the energy in the original ejecta is quickly transferred to the ambient medium and propagates farther into the medium as a blast wave. Here we report the detection of circularly polarized light in the afterglow of GRB 121024A, measured 0.15 days after the burst. We show that the circular polarization is intrinsic to the afterglow and unlikely to be produced by dust scattering or plasma propagation effects. A possible explanation is to invoke anisotropic (rather than the commonly assumed isotropic) electron pitch-angle distributions, and we suggest that new models are required to produce the complex microphysics of realistic shocks in relativistic jets.

  16. Circular polarization in the optical afterglow of GRB 121024A.

    PubMed

    Wiersema, K; Covino, S; Toma, K; van der Horst, A J; Varela, K; Min, M; Greiner, J; Starling, R L C; Tanvir, N R; Wijers, R A M J; Campana, S; Curran, P A; Fan, Y; Fynbo, J P U; Gorosabel, J; Gomboc, A; Götz, D; Hjorth, J; Jin, Z P; Kobayashi, S; Kouveliotou, C; Mundell, C; O'Brien, P T; Pian, E; Rowlinson, A; Russell, D M; Salvaterra, R; di Serego Alighieri, S; Tagliaferri, G; Vergani, S D; Elliott, J; Fariña, C; Hartoog, O E; Karjalainen, R; Klose, S; Knust, F; Levan, A J; Schady, P; Sudilovsky, V; Willingale, R

    2014-05-01

    Gamma-ray bursts (GRBs) are most probably powered by collimated relativistic outflows (jets) from accreting black holes at cosmological distances. Bright afterglows are produced when the outflow collides with the ambient medium. Afterglow polarization directly probes the magnetic properties of the jet when measured minutes after the burst, and it probes the geometric properties of the jet and the ambient medium when measured hours to days after the burst. High values of optical polarization detected minutes after the burst of GRB 120308A indicate the presence of large-scale ordered magnetic fields originating from the central engine (the power source of the GRB). Theoretical models predict low degrees of linear polarization and no circular polarization at late times, when the energy in the original ejecta is quickly transferred to the ambient medium and propagates farther into the medium as a blast wave. Here we report the detection of circularly polarized light in the afterglow of GRB 121024A, measured 0.15 days after the burst. We show that the circular polarization is intrinsic to the afterglow and unlikely to be produced by dust scattering or plasma propagation effects. A possible explanation is to invoke anisotropic (rather than the commonly assumed isotropic) electron pitch-angle distributions, and we suggest that new models are required to produce the complex microphysics of realistic shocks in relativistic jets. PMID:24776800

  17. A CORRELATED STUDY OF OPTICAL AND X-RAY AFTERGLOWS OF GRBs

    SciTech Connect

    Li, Liang; Ryde, Felix; Wu, Xue-Feng; Huang, Yong-Feng; Tang, Qing-Wen; Geng, Jin-Jun; Wang, Xiang-Gao; Liang, En-Wei; Liang, Yun-Feng; Zhang, Bin-Bin; Wang, Yu; Wei, Jian-Yan; Zhang, Bing E-mail: liang.li@fysik.su.se

    2015-05-20

    We study an extensive sample of 87 gamma-ray bursts (GRBs) for which there are well-sampled and simultaneous optical and X-ray light curves. We extract the cleanest possible signal of the afterglow component and compare the temporal behaviors of the X-ray light curve, observed by Swift XRT, and optical data, observed by UVOT and ground-based telescopes for each individual burst. Overall we find that 62% of the GRBs are consistent with the standard afterglow model. When more advanced modeling is invoked, up to 91% of the bursts in our sample may be consistent with the external-shock model. A large fraction of these bursts are consistent with occurring in a constant interstellar density medium (61%) while only 39% of them occur in a wind-like medium. Only nine cases have afterglow light curves that exactly match the standard fireball model prediction, having a single power-law decay in both energy bands that are observed during their entire duration. In particular, for the bursts with chromatic behavior, additional model assumptions must be made over limited segments of the light curves in order for these bursts to fully agree with the external-shock model. Interestingly, for 54% of the X-ray and 40% of the optical band observations, the end of the shallow decay (t{sup ∼−0.5}) period coincides with the jet-break (t{sup ∼−p}) time, causing an abrupt change in decay slope. The fraction of the burst that is consistent with the external-shock model is independent of the observational epochs in the rest frame of GRBs. Moreover, no cases can be explained by the cooling frequency crossing the X-ray or optical band.

  18. Gamma-ray burst afterglows as probes of their host galaxies and the cosmos

    NASA Astrophysics Data System (ADS)

    Cucchiara, Antonino

    2010-12-01

    Gamma-ray Bursts (GRBs) represent the sole class of catastrophic phenomena seen over almost the entire history of the Universe. Their extreme luminosities in high energy gamma-ray radiation make them readily detectable, even with relatively small satellite-based detectors, out to the earliest cosmic epochs. Moreover, the brilliance of their fading afterglow light, routinely observed in X-ray, optical, near-infrared, and radio wavelengths, allows them to be exploited -- for hours, days, or weeks -- as cosmic lighthouses, probing the conditions of gas and dust along the line of sight, through their host galaxies and the cosmos at large. Since the November 2004 launch of Swift, this GRB-focused NASA mission has discovered more than 500 GRBs, in almost all cases reporting the burst coordinates to ground-based observers within seconds of the event. The availability of prompt burst positions from Swift, combined with promptly-reported flux measurements from instruments on Swift and an array of ground-based robotic telescopes, have enabled targeted spectroscopic campaigns that have gathered detailed observations of the young, bright afterglows of hundreds of these events. This thesis reports the results of my own efforts over the past 5 years, analyzing imaging and spectroscopic observations of Swift-detected GRBs as triggered according to my own requests, or as gathered from public data archives. In Chapter 2, I discuss our follow-up campaign for GRB090429B, one of our best "extreme redshift" (z > 8) candidates. This burst followed closely on the spectroscopicallyconfirmed z = 8.2 GRB090423, and our multiwavelength observations and SED modeling demonstrate the value and limitation of such studies, in cases where a spectroscopic redshift cannot be gathered in a timely fashion. I also address the importance of such extreme-redshift events from a cosmological perspective. In Chapter 3, I use high-resolution GRB afterglow spectra to study the properties of intervening

  19. Afterglow processes responsible for memory effect in nitrogen

    SciTech Connect

    Pejovic, M. M.; Nesic, N. T.; Pejovic, M. M.; Zivanovic, E. N.

    2012-07-01

    The mechanisms responsible for memory effect in nitrogen at 6.6 mbars have been analysed based on experimental data of electrical breakdown time delay as a function of afterglow period. The analysis has shown that positive ions remaining from previous discharge, as well as metastable and highly vibrationally excited molecules, are responsible for memory effect in the early afterglow. These molecules lead to the formation of positive ions in mutual collisions in the afterglow. Positive ions initiate secondary electron emission from the cathode of a nitrogen-filled tube when voltage higher than static breakdown voltage is applied on the electrodes. On the other hand, N({sup 4}S) atoms have a large influence on memory effect in late afterglow. They recombine on the cathode surface forming metastable molecules, which release secondary electrons in collision with the cathode. The higher values of electrical breakdown time delay in the case of the tube with borosilicate glass walls than in the case of the tube with copper walls are a consequence of faster de-excitation of neutral active particles on the glass. Indirect confirmation of this assumption has been obtained when the tubes were irradiated with gamma radiation.

  20. Afterglow processes responsible for memory effect in nitrogen

    NASA Astrophysics Data System (ADS)

    Pejović, M. M.; Nešić, N. T.; Pejović, M. M.; Živanović, E. N.

    2012-07-01

    The mechanisms responsible for memory effect in nitrogen at 6.6 mbars have been analysed based on experimental data of electrical breakdown time delay as a function of afterglow period. The analysis has shown that positive ions remaining from previous discharge, as well as metastable and highly vibrationally excited molecules, are responsible for memory effect in the early afterglow. These molecules lead to the formation of positive ions in mutual collisions in the afterglow. Positive ions initiate secondary electron emission from the cathode of a nitrogen-filled tube when voltage higher than static breakdown voltage is applied on the electrodes. On the other hand, N(S4) atoms have a large influence on memory effect in late afterglow. They recombine on the cathode surface forming N2(AΣ3u+) metastable molecules, which release secondary electrons in collision with the cathode. The higher values of electrical breakdown time delay in the case of the tube with borosilicate glass walls than in the case of the tube with copper walls are a consequence of faster de-excitation of neutral active particles on the glass. Indirect confirmation of this assumption has been obtained when the tubes were irradiated with gamma radiation.

  1. ON PARTICLE ACCELERATION RATE IN GAMMA-RAY BURST AFTERGLOWS

    SciTech Connect

    Sagi, Eran; Nakar, Ehud

    2012-04-10

    It is well known that collisionless shocks are major sites of particle acceleration in the universe, but the details of the acceleration process are still not well understood. The particle acceleration rate, which can shed light on the acceleration process, is rarely measured in astrophysical environments. Here, we use observations of gamma-ray burst (GRB) afterglows, which are weakly magnetized relativistic collisionless shocks in ion-electron plasma, to constrain the rate of particle acceleration in such shocks. We find, based on X-ray and GeV afterglows, an acceleration rate that is most likely very fast, approaching the Bohm limit, when the shock Lorentz factor is in the range of {Gamma} {approx} 10-100. In that case X-ray observations may be consistent with no amplification of the magnetic field in the shock upstream region. We examine the X-ray afterglow of GRB 060729, which is observed for 642 days showing a sharp decay in the flux starting about 400 days after the burst, when the shock Lorentz factor is {approx}5. We find that inability to accelerate X-ray-emitting electrons at late time provides a natural explanation for the sharp decay, and that also in that case acceleration must be rather fast, and cannot be more than a 100 times slower than the Bohm limit. We conclude that particle acceleration is most likely fast in GRB afterglows, at least as long as the blast wave is ultrarelativistic.

  2. Optical and X-Ray Observations of GRB 060526: A Complex Afterglow Consistent with an Achromatic Jet Break

    NASA Technical Reports Server (NTRS)

    Dai, X.; Halpern, J. P.; Morgan, N. D.; Armstrong, E.; Mirabal, N.; Haislip. J. B.; Reichart, D. E.; Stanek, K. Z.

    2007-01-01

    We obtained 98 R-band and 18 B, r', i' images of the optical afterglow of GRB 060526 (z = 3.21) with the MDM 1.3 m, 2.4 m, and the PROMPT telescopes at CTIO over the five nights following the burst trigger. Combining these data with other optical observations reported in GCN and the Swift XRT observations, we compare the optical and X-ray afterglow light curves of GRB 060526. Both the optical and X-ray afterglow light curves show rich features, such as flares and breaks. The densely sampled optical observations provide very good coverage at T > 10(exp 4) s. We observed a break at 2.4 x 10(exp 5) sin the optical afterglow light curve. Compared with the X-ray afterglow light curve, the break is consistent with an achromatic break supporting the beaming models of GRBs. However, the prebreak and postbreak temporal decay slopes are difficult to explain in simple afterglow models. We estimated a jet angle of theta(sub j) approx. 7deg and a prompt emission size of R(sub prompt) approx. 2 x 10(exp 14) cm. In addition, we detected several optical flares with amplitudes of (Delta)m approx. 0.2,0.6, and 0.2 mag. The X-ray afterglows detected by Swift have shown complicated decay patterns. Recently, many well-sampled optical afterglows also show decays with flares and multiple breaks. GRB 060526 provides an additional case of such a complex, well-observed optical afterglow. The accumulated well-sampled afterglows indicate that most of the optical afterglows are complex.

  3. Influence of the ambipolar-to-free diffusion transition on dust particle charge in a complex plasma afterglow

    SciTech Connect

    Coueedel, L.; Mikikian, M.; Boufendi, L.

    2008-06-15

    The influence of diffusive losses on residual dust charge in a complex plasma afterglow has been investigated. The residual charge distribution was measured and exhibits a mean value Q{sub dres}{approx}(-3e-5e) with a tail in the positive region. The experimental results have been compared with simulated charge distributions. The dust residual charges were simulated based on a model developed to describe complex plasma decay. The experimental and simulated data show that the transition from ambipolar to free diffusion in the decaying plasma plays a significant role in determining the residual dust particle charges. The presence of positively charged dust particles is explained by a broadening of the charge distribution function in the afterglow plasma.

  4. The SEDs and Host Galaxies of the Dustiest GRB Afterglows

    NASA Technical Reports Server (NTRS)

    Kruhler, T.; Greiner, J.; Schady, P.; Savaglio, S.; Afonso, P. M. J.; Clemens, C.; Elliott, J.; Filgas, R.; Gruber, D.; Kann, D. A.; Klose, S.; Kupcu-Yoldas, A.; McBreen, S.; Olivares, E.; Pierini, D.; Rau, A.; Rossi, A.; Nardini, M.; Nicuesa Guelbenzu, A.; Sudilovsky, V.; Updike, A. C.

    2011-01-01

    The afterglows and host galaxies of long gamma-ray bursts (GRBs) offer unique opportunities to study star-forming galaxies in the high-z Universe, Until recently, however. the information inferred from GRB follow-up observations was mostly limited to optically bright afterglows. biasing all demographic studies against sight-lines that contain large amounts of dust. Aims. Here we present afterglow and host observations for a sample of bursts that are exemplary of previously missed ones because of high visual extinction (A(sub v) (Sup GRB) approx > 1 mag) along the sight-line. This facilitates an investigation of the properties, geometry and location of the absorbing dust of these poorly-explored host galaxies. and a comparison to hosts from optically-selected samples. Methods. This work is based on GROND optical/NIR and Swift/XRT X-ray observations of the afterglows, and multi-color imaging for eight GRB hosts. The afterglow and galaxy spectral energy distributions yield detailed insight into physical properties such as the dust and metal content along the GRB sight-line as well as galaxy-integrated characteristics like the host's stellar mass, luminosity. color-excess and star-formation rate. Results. For the eight afterglows considered in this study we report for the first time the redshift of GRBs 081109 (z = 0.97S7 +/- 0.0005). and the visual extinction towards GRBs 0801109 (A(sub v) (Sup GRB) = 3.4(sup +0.4) (sub -0.3) mag) and l00621A (A(sub v) (Sup GRB) = 3.8 +/- 0.2 mag), which are among the largest ever derived for GRB afterglows. Combined with non-extinguished GRBs. there is a strong anti-correlation between the afterglow's metals-to-dust ratio and visual extinction. The hosts of the dustiest afterglows are diverse in their properties, but on average redder(((R - K)(sub AB)) approximates 1.6 mag), more luminous ( approximates 0.9 L (sup *)) and massive ((log M(sup *) [M(solar]) approximates 9.8) than the hosts of optically-bright events. We hence probe

  5. GRB 110731A: Early Afterglow in Stellar Wind Powered By a Magnetized Outflow

    NASA Astrophysics Data System (ADS)

    Fraija, N.

    2015-05-01

    One of the most energetic gamma-ray bursts, GRB 110731A, was observed from an optical to GeV energy range. Previous analysis of the prompt phase revealed similarities between the Large Area Telescope (LAT) bursts observed by Fermi: (1) a delayed onset of the high-energy emission (\\gt 100 MeV), (2) a short-lasting bright peak at later times, and (3) a temporally extended component from this phase, lasting hundreds of seconds. Additionally to the prompt phase, multiwavelength observations over different epochs showed that the spectral energy distribution was better fitted by a wind afterglow model. We present a leptonic model based on an early afterglow that evolves in a stellar wind of its progenitor. We apply this model to interpret the temporally extended LAT emission and the brightest LAT peak exhibited by the prompt phase of GRB 110731A. Additionally, using the same set of parameters, we describe the multiwavelength afterglow observations. The origin of the temporally extended LAT, X-ray, and optical flux is explained through synchrotron radiation from the forward shock (FS) and the brightest LAT peak is described, evoking the synchrotron self-Compton emission from the reverse shock (RS). The bulk Lorentz factor required in this model (Γ ≃ 520) lies in the range of values demanded for most LAT-detected GRBs. We show that the strength of the magnetic field in the RS region is ∼50 times stronger than that in the FS region. This result suggests that, for GRB 110731A, the central engine is likely entrained with strong magnetic fields.

  6. Short GRB Prompt and Afterglow Correlations

    NASA Technical Reports Server (NTRS)

    Gehrels, Neil

    2007-01-01

    The Swift data set on short GRBs has now grown large enough to study correlations of key parameters. The goal is to compare long and short bursts to better understand similarities and differences in the burst origins. In this study we consider the both prompt and afterglow fluxes. It is found that the optical, X-ray and gamma-ray emissions are linearly correlated - stronger bursts tend to have brighter afterglows, and bursts with brighter X-ray afterglow tend to have brighter optical afterglow. Both the prompt and afterglow fluxes are, on average, lower for short bursts than for long. Although there are short GRBs with undetected optical emission, there is no evidence for "dark" short bursts with anomalously low opt/X ratios. The weakest short bursts have a low X-ray/gamma-ray ratio.

  7. Synchrotron and inverse-Compton emissions from pairs formed in GRB afterglows (analytical treatment)

    SciTech Connect

    Panaitescu, A.; Vestrand, W. T.

    2014-10-01

    We calculate the synchrotron and inverse-Compton emissions from pairs formed in gamma-ray burst (GRB) afterglows from high-energy photons (above 100 MeV), assuming a power-law photon spectrum C {sub ν}∝ν{sup –2} and considering only the pairs generated from primary high-energy photons. The essential properties of these pairs (number, minimal energy, cooling energy, distribution with energy) and of their emission (peak flux, spectral breaks, spectral slope) are set by the observables GeV fluence Φ(t) = Ft and spectrum, and by the Lorentz factor, Γ, and magnetic field, B, of the source of high-energy photons, at observer time, t. Optical and X-ray pseudo light curves, F {sub ν}(Γ), are calculated for the given B; proper synchrotron self-Compton light curves are calculated by setting the dynamics Γ(t) of the high-energy photon source to be that of a decelerating, relativistic shock. It is found that the emission from pairs can accommodate the flux and decays of the optical flashes measured during the prompt (GRB) phase, but it decays faster than the X-ray plateaus observed during the delayed (afterglow) phase. The brightest pair optical emission is obtained for 100 < Γ < 500, and depends mostly on the GeV fluence, being independent of the source redshift. Emission from pairs formed during the GRB phase offers an alternate explanation to reverse-shock optical flashes. These two models may be distinguished based on their corresponding flux decay index-spectral slope relations, different correlations with the Large Area Telescope fluence, or through modeling of the afterglow multiwavelength data.

  8. DISCOVERY OF A TIGHT CORRELATION FOR GAMMA-RAY BURST AFTERGLOWS WITH 'CANONICAL' LIGHT CURVES

    SciTech Connect

    Dainotti, Maria Giovanna; Ostrowski, Michal; Willingale, Richard; Capozziello, Salvatore; Cardone, Vincenzo Fabrizio E-mail: mio@oa.uj.edu.p E-mail: capozziello@na.infn.i

    2010-10-20

    Gamma-ray bursts (GRBs) observed up to redshifts z>8 are fascinating objects to study due to their still unexplained relativistic outburst mechanisms and their possible use to test cosmological models. Our analysis of 77 GRB afterglows with known redshifts revealed a physical subsample of long GRBs with the canonical plateau breaking to power-law light curves with a significant luminosity L*{sub X}-break time T*{sub a} correlation in the GRB rest frame. This subsample forms approximately the upper envelope of the studied distribution. We have also found a similar relation for a small sample of GRB afterglows that belong to the intermediate class between the short and the long ones. It proves that within the full sample of afterglows there exist physical subclasses revealed here by tight correlations of their afterglow properties. The afterglows with regular ('canonical') light curves obey not only the mentioned tight physical scaling, but-for a given T*{sub a}-the more regular progenitor explosions lead to preferentially brighter afterglows.

  9. GRB 081029: A Gamma-Ray Burst with a Multi-Component Afterglow

    NASA Technical Reports Server (NTRS)

    Holland, Stephen T.; De Pasquale, Massimiliano; Mao, Jirong; Sakamoto, Takanori; Schady, Patricia; Covino, Stefano; Fan, Yi-Zhong; Jin, Zhi-Ping; D'Avanzo, Paolo; Antonelli, Angelo; D'Elia, Valerio; Ohincarini, Guido; Fiore, Fabrizio; Pandey, Shashi Bhushan; Cobb, Bethany E.

    2012-01-01

    We present an analysis of the unusual optical light curve of the gamma-ray burst GRB 081029, a long-soft burst with a redshift of z = 3.8479. We combine X-ray and optical observations from the Swift X-Ray Telescope and the Swift Ultra Violet/Optical Telescope with ground-based optical and infrared data obtained using the REM, ROTSE, and CTIO 1.3-m telescopes to construct a detailed data set extending from 86 s to approx.100,000 s after the BAT trigger. Our data covers a wide energy range, from 10 keV to 0.77 eV (1.24 A to 16000 A). The X-ray afterglow shows a shallow initial decay followed by a rapid decay starting at about 18,000 s. The optical and infrared afterglow, however, shows an uncharacteristic rise at about 3000 s that does not correspond to any feature in the X-ray light curve. Our data are not consistent with synchrotron radiation from a jet interacting with an external medium, a two-component jet, or continuous energy injection from the central engine. We find that the optical light curves can be broadly explained by a collision between two ejecta shells within a two-component jet. A growing number of gamma-ray burst afterglows are consistent with complex jets, which suggests that some (or all) gamma-ray burst jets are complex and will require detailed modelling to fully understand them.injection

  10. Kinetic study on non-thermal volumetric plasma decay in the early afterglow of air discharge generated by a short pulse microwave or laser

    NASA Astrophysics Data System (ADS)

    Yang, Wei; Zhou, Qianhong; Dong, Zhiwei

    2016-08-01

    This paper reports a kinetic study on non-thermal plasma decay in the early afterglow of air discharge generated by short pulse microwave or laser. A global self-consistent model is based on the particle balance of complex plasma chemistry, electron energy equation, and gas thermal balance equation. Electron-ion Coulomb collision is included in the steady state Boltzmann equation solver to accurately describe the electron mobility and other transport coefficients. The model is used to simulate the afterglow of microsecond to nanosecond pulse microwave discharge in N2, O2, and air, as well as femtosecond laser filament discharge in dry and humid air. The simulated results for electron density decay are in quantitative agreement with the available measured ones. The evolution of plasma decay under an external electric field is also investigated, and the effect of gas heating is considered. The underlying mechanism of plasma density decay is unveiled through the above kinetic modeling.

  11. The afterglow and the host galaxy of GRB 011211

    NASA Astrophysics Data System (ADS)

    Jakobsson, P.; Hjorth, J.; Fynbo, J. P. U.; Gorosabel, J.; Pedersen, K.; Burud, I.; Levan, A.; Kouveliotou, C.; Tanvir, N.; Fruchter, A.; Rhoads, J.; Grav, T.; Hansen, M. W.; Michelsen, R.; Andersen, M. I.; Jensen, B. L.; Pedersen, H.; Thomsen, B.; Weidinger, M.; Bhargavi, S. G.; Cowsik, R.; Pandey, S. B.

    2003-09-01

    We present optical, near-infrared, and X-ray observations of the optical afterglow (OA) of the X-ray rich, long-duration gamma-ray burst GRB 011211. Hubble Space Telescope (HST) data obtained 14, 26, 32, and 59 days after the burst, show the host galaxy to have a morphology that is fairly typical of blue galaxies at high redshift. We measure its magnitude to be R = 24.95 +/- 0.11. We detect a break in the OA R-band light curve which is naturally accounted for by a collimated outflow geometry. By fitting a broken power-law to the data we find a best fit with a break 1.56 +/- 0.02 days after the burst, a pre-break slope of alpha1 = -0.95 +/- 0.02, and a post-break slope of alpha2 = -2.11 +/- 0.07. The UV-optical spectral energy distribution (SED) around 14 hours after the burst is best fit with a power-law with index beta = -0.56 +/- 0.19 reddened by an SMC-like extinction law with a modest AV = 0.08 +/- 0.08 mag. By comparison, from the XMM-Newton X-ray data at around the same time, we find a decay index of alphaX = -1.62 +/- 0.36 and a spectral index of betaX = -1.21+0.10-0.15. Interpolating between the UV-optical and X-ray implies that the cooling frequency is located close to ~ 1016 Hz in the observer frame at the time of the observations. We argue, using the various temporal and spectral indices above, that the most likely afterglow model is that of a jet expanding into an external environment that has a constant mean density rather than a wind-fed density structure. We estimate the electron energy index for this burst to be p ~ 2.3. Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden. Based on observations made with ESO Telescopes at the Paranal Observatory by GRACE under programme ID 69.D-0701. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the

  12. Study of argon flowing afterglow with nitrogen injection

    SciTech Connect

    Mazánková, V.; Krčma, F.; Trunec, D.

    2013-10-28

    In this work, the reaction kinetics in argon flowing afterglow with nitrogen addition was studied by optical emission spectroscopy. The DC flowing post-discharge in pure argon was created in quartz tube at the total gas pressure of 1000 Pa and discharge power of 60 W. The nitrogen was added into the afterglow at the distance of 9 cm behind the active discharge. The optical emission spectra were measured along the flow tube. The argon spectral lines and after nitrogen addition also nitrogen second positive system (SPS) were identified in the spectra. The measurement of spatial dependence of SPS intensity showed a very slow decay of the intensity and the decay rate did not depend on the nitrogen concentration. In order to explain this behavior a kinetic model for reaction in afterglow was developed. This model showed that C {sup 3}Π{sub u} state of molecular nitrogen, which is the upper state of SPS emission, is produced by excitation transfer from argon metastables to nitrogen molecules. However, the argon metastables are also produced at Ar{sub 2}{sup +} ion recombination with electrons and this limits the decay of argon metastable concentration and it results in very slow decay of SPS intensity.

  13. The Late Afterglow and Host Galaxy of GRB 990712.

    PubMed

    Hjorth; Holland; Courbin; Dar; Olsen; Scodeggio

    2000-05-10

    We present deep Hubble Space Telescope (HST) imaging, as well as ground-based imaging and spectroscopy, of the optical afterglow associated with the long-duration gamma-ray burst GRB 990712 and its host galaxy. The data were obtained 48-123 days after the burst occurred. The magnitudes of the host (R=21.9, V=22.5) and optical afterglow (R=25.4, V=25.8, 47.7 days after the burst) favor a scenario in which the optical light follows a pure power-law decay with an index of alpha approximately -1.0. We find no evidence for a contribution from a supernova like SN 1998bw. This suggests that either there are multiple classes of long-duration gamma-ray bursts or that the peak luminosity of the supernova was more than 1.5 mag fainter than SN 1998bw. The HST images and EFOSC2 spectra indicate that the gamma-ray burst was located in a bright, extended feature (possibly a star-forming region) 1.4 kpc from the nucleus of a 0.2L*B galaxy at z=0.434, possibly a Seyfert 2 galaxy. The late-time afterglow and host galaxy of GRB 990712 bear some resemblance to those of GRB 970508. PMID:10813669

  14. Gamma-Ray Bursts and Afterglows: a Multi-Wavelength Study in the Swift Era

    NASA Astrophysics Data System (ADS)

    Yu, Y. W.

    2010-01-01

    Gamma-ray bursts (GRBs), which are generally followed by long-lasting low-frequency afterglow emission, are short and intense pulses of gamma-rays observed from the sky in arbitrary directions. In order to observe the multi-wavelength emission at the early afterglow phase and even the prompt emission phase, NASA launched the Swift satellite on Nov. 20th 2004. Swift can localize GRBs within about 10 seconds. A brief review on the recent progress in observations and theories in the Swift era is given in Chapter 1. This paper focuses on the features of the early afterglows and the multi-wavelength prompt emission. In Chapters 2 and 3, we try to explain the shallow-decaying X-ray afterglows and X-ray flares, both of which are unaccountable in the standard afterglow model. (1) It is widely accepted that the shallow decay phase indicates a continuous energy injection into the GRB blast wave, and this energy could be released from the central engine after the burst. Based on the knowledge of the evolution of a pulsar wind, we argue that the injected flow interacting with the GRB blast wave is an ultra-relativistic kinetic-energy flow (i.e., wind) rather than pure electromagnetic waves. Therefore, a relativistic wind bubble (RWB) including a pair of shocks will be formed. Our numerical calculations and the fitting results show that the emission from an RWB can well account for the X-ray shallow decay phase. (2) For the X-ray flares that are attributed to some intermediate late activities of the central engine, we analyze the detailed dynamics of late internal shocks which directly produce the flare emission. Comparing the theoretical results with the lower limits of the observational luminosities and the profiles of the flare light curves, we find some constraints on the properties of the pre-collision shells, which are directly determined by the central object. In Chapter 4, we investigate the high-energy afterglow emission during the shallow decay phase in two models, i

  15. Gamma-Ray Bursts and Afterglows: a Multi-Wavelength Study in the Swift Era

    NASA Astrophysics Data System (ADS)

    Yu, Y. W.

    2010-01-01

    Gamma-ray bursts (GRBs), which are generally followed by long-lasting low-frequency afterglow emission, are short and intense pulses of gamma-rays observed from the sky in arbitrary directions. In order to observe the multi-wavelength emission at the early afterglow phase and even the prompt emission phase, NASA launched the Swift satellite on Nov. 20th 2004. Swift can localize GRBs within about 10 seconds. A brief review on the recent progress in observations and theories in the Swift era is given in Chapter 1. This paper focuses on the features of the early afterglows and the multi-wavelength prompt emission. In Chapters 2 and 3, we try to explain the shallow-decaying X-ray afterglows and X-ray flares, both of which are unaccountable in the standard afterglow model. (1) It is widely accepted that the shallow decay phase indicates a continuous energy injection into the GRB blast wave, and this energy could be released from the central engine after the burst. Based on the knowledge of the evolution of a pulsar wind, we argue that the injected flow interacting with the GRB blast wave is an ultra-relativistic kinetic-energy flow (i.e., wind) rather than pure electromagnetic waves. Therefore, a relativistic wind bubble (RWB) including a pair of shocks will be formed. Our numerical calculations and the fitting results show that the emission from an RWB can well account for the X-ray shallow decay phase. (2) For the X-ray flares that are attributed to some intermediate late activities of the central engine, we analyze the detailed dynamics of late internal shocks which directly produce the flare emission. Comparing the theoretical results with the lower limits of the observational luminosities and the profiles of the flare light curves, we find some constraints on the properties of the pre-collision shells, which are directly determined by the central object. In Chapter 4, we investigate the high-energy afterglow emission during the shallow decay phase in two models, i

  16. Gamma-ray burst radio afterglows from Population III stars: simulation methods and detection prospects with SKA precursors

    NASA Astrophysics Data System (ADS)

    Macpherson, D.; Coward, D.

    2015-10-01

    We investigate the prospects of detecting radio afterglows from long Gamma-Ray Bursts (GRBs) from Population III (Pop III) progenitors using the Square Kilometre Array (SKA) precursor instruments MWA (Murchison Widefield Array) and ASKAP (Australian SKA Pathfinder). We derive a realistic model of GRB afterglows that encompasses the widest range of plausible physical parameters and observation angles. We define the best case scenario of Pop III GRB energy and redshift distributions. Using probability distribution functions fitted to the observed microphysical parameters of long GRBs, we simulate a large number of Pop III GRB afterglows to find the global probability of detection. We find that ASKAP may be able to detect 35 per cent of Pop III GRB afterglows in the optimistic case, and 27 per cent in the pessimistic case. A negligible number will be detectable by MWA in either case. Detections per image for ASKAP, found by incorporating intrinsic rates with detectable time-scales, are as high as ˜6000 and as low as ˜11, which shows the optimistic case is unrealistic. We track how the afterglow flux density changes over various time intervals and find that, because of their very slow variability, the cadence for blind searches of these afterglows should be as long as possible. We also find Pop III GRBs at high redshift have radio afterglow light curves that are indistinguishable from those of regular long GRBs in the more local Universe.

  17. The Radio Afterglow of GRB030329 at Centimetre Wavelengths: Evidence for Multiple Jets or a Structured Jet. Chapter 6

    NASA Technical Reports Server (NTRS)

    Rol, E.; vanderHorst, A. J.; Wijers, R. A. M. J.; Strom, R.; Kaper, L.; Kouveliotou, C.; vandenHeuvel, E. P. J.

    2003-01-01

    We present our centimetre wavelength (1.4, 2.3 and 4.9 GHz) light curves of the afterglow of GRB030329, which were obtained with the Westerbork Synthesis Radio Telescope. Modelling the data according to a collimated afterglow results in a jet-break time t(sub j) of 17 days. This is in contrast with earlier results obtained at higher frequencies, which indicate t(sub j) to be around 10 days. Furthermore, with respect to the afterglow model, some additional flux at the lower frequencies is present when these light curves reach their maximum. We subsequently show that the afterglow can be modelled with two or more components with progressively later jet breaks. From these results we infer that the jet is in fact a structured or a layered jet, where the ejecta with lower Lorentz factors produce additional flux which becomes visible at late times in the lowest frequency bands.

  18. Emission spectrum of a sporadic fireball afterglow

    NASA Astrophysics Data System (ADS)

    Madiedo, J.; Trigo-Rodríguez, J.

    2014-07-01

    A mag. -11 fireball was imaged over southern Spain on April 14, 2013 at 22:35:49.8 ± 0.1s UTC. Its emission spectrum was also obtained. This event was assigned the SPMN code 140413 after the recording date. By the end of its atmospheric path, it exhibited a very bright flare which resulted in a persistent train whose spectrum was recorded. Here we present a preliminary analysis of this event and focus special attention on the evolution of the main emission lines in the spectrum of the afterglow. An array of low-lux CCD video devices (models 902H and 902H Ultimate from Watec Co.) operating from our stations at Sevilla and El Arenosillo was employed to record the SPMN140413 fireball. The operation of these systems is explained in [1,2]. Some of these are configured as spectrographs by attaching holographic diffraction gratings (1000 lines/mm) to the objective lens [3]. To calculate the atmospheric trajectory, radiant, and orbit we have employed our AMALTHEA software, which follows the planes intersection method [4]. The spectrum was analyzed with our CHIMET application [5]. The parent meteoroid impacted the atmosphere with an initial velocity of 28.9 ± 0.3 km/s and the fireball began at a height of 104.4 ± 0.5 km. The event ended at 80.7 ± 0.5 km above the ground level, with the main flare taking place at 83 ± 0.5 km. The calculated radiant and orbital parameters confirm the sporadic nature of the bolide. The calibrated emission spectrum shows that the most important contributions correspond to the Na I-1 (588.9 nm) and Mg I-2 (517.2 nm) multiplets. In the ultraviolet, the contribution from the H and K lines from Ca was also identified. As usual in meteor spectra, most of the lines correspond to Fe I. The train spectrum was recorded during about 0.12 seconds. This provided the evolution with time of the intensity of the emission lines in this signal. The contributions from Mg I, Na I, Ca I, Fe I, Ca II, and O I were identified in the afterglow, with the Na I-1

  19. The late X-ray afterglow of gamma-ray bursts.

    PubMed

    Willingale, Richard; O'Brien, Paul T

    2007-05-15

    We have developed a functional fit which can be used to represent the entire temporal decay of the X-ray afterglow of gamma-ray bursts (GRBs). The fit delineates and parameterizes well-defined phases for the decay: the prompt emission; an initial steep decay; a shallow plateau phase; and finally, a powerlaw afterglow. For 20% of GRBs, the plateau phase is weak, or not seen, and the initial powerlaw decay becomes the final afterglow.We compare the temporal decay parameters and X-ray spectral indices for 107 GRBs discovered by Swift with the expectations of the standard fireball model including a search for possible jet breaks. For approximately 50% of GRBs, the observed afterglow is in accord with the model, but for the rest the temporal and spectral properties are not as expected. We identify a few possible jet breaks, but there are many examples where such breaks are predicted but are absent. We also find that the start time of the final afterglow decay, Ta, is associated with the peak of the prompt gamma-ray emission spectrum, Epeak, just as optical jet-break times, tj, are associated with Epeak in the Ghirlanda relation.

  20. Shallow Decay of Early X-Ray Afterglows from Inhomogeneous Gamma-Ray Burst Jets

    NASA Astrophysics Data System (ADS)

    Toma, Kenji; Ioka, Kunihito; Yamazaki, Ryo; Nakamura, Takashi

    2006-04-01

    Almost all the X-ray afterglows of γ-ray bursts (GRBs) observed by the Swift satellite have a shallow decay phase in their first few thousand seconds. We show that in an inhomogeneous-jet model (multiple-subjet or patchy-shell), the superposition of the afterglows of off-axis subjets (patchy shells) can produce the shallow decay phase. The necessary condition for obtaining the shallow decay phase is that γ-ray-bright subjets (patchy shells) have γ-ray efficiencies higher than previously estimated and that they be surrounded by γ-ray-dim subjets (patchy shells) with low γ-ray efficiency. Our model predicts that events with dim prompt emission will have a conventional afterglow light curve without a shallow decay phase, like GRB 050416A.

  1. The Late Peaking Afterglow of GR8 100418A

    NASA Technical Reports Server (NTRS)

    Marshall, Frank; Antonelli, L. A.; Burrows, D. N.; Covino, S.; dePasquale, M.; Evans, P. A.; Fugazza, D.; Holland, S. T.; Liang, E. W.; OBrien, P. T.; Osborne, J. P.; Pagani, C.; Sakamoto, T.; Siegel, M. H.; Wu, X. F.; Zhang, B.

    2010-01-01

    GRB 100418A is a long Gamma-Ray Burst at redshift z=0.6235 discovered with the Swift Gamma-Ray Burst Explorer with unusual optical and X-ray light curves ' After an initial short-lived, rapid decline in X-rays, the optical and X-ray light curves observed with Swift are approximately flat or rising slightly out to at least approx.7 ks after the trigger, peak at approx.50 ks, and then follow an approximately power-law decay. Such a long optical plateau and late peaking is rarely seen in 6R8 afterglows. Observations with REM during a gap in the Swift coverage indicate a bright optical flare at approx.25 ks, The long plateau phase of the afterglow is interpreted using either a model with continuous injection of energy into the forward shock of the burst or a model in which the 'et of the burst is viewed off-axis. In both models the isotropic kinetic energy in the late afterglow after the plateau phase is >100 times the 10(exp 51) erg of the prompt isotropic gamma-ray energy release. The energy injection model is favored because the off-axis 'et model would require the intrinsic $T f801$ for the GR8 'et viewed on-axis to be very short, approx.10 ms, and the intrinsic isotropic gamma-ray energy release and the true jet energy to be much higher than the typical values of known short GRBs^ The non-detection of a 'et break up to approx.2 Ms indicates a jet half-opening angle of at least 14 degrees, and a relatively high collimation-corrected 'et energy of at least 10(exp 52) erg.

  2. GRB afterglows in the nonrelativistic phase

    NASA Astrophysics Data System (ADS)

    Huang, Y. F.; Lu, T.

    2008-10-01

    When discussing the afterglows of gamma-ray bursts analytically, it is usually assumed that the external shock is always ultra-relativisitc, with the bulk Lorentz factor much larger than 1. However, we show that the deceleration of the external shock is actually very quick. The afterglow may typically enter the nonrelativistic phase in several days to teens of days, and may even enter the deep Newtonian phase in tens of days to several months. One thus should be careful in using those familiar analytical expressions that are derived only under the ultra-relativistic assumption. To explain the observed afterglows that typically last for a few weeks to several months, we need to consider the dynamics and radiation in the nonrelativisitic phase.

  3. Processes in afterglow responsible for initiation of electrical breakdown in xenon at low pressure

    NASA Astrophysics Data System (ADS)

    Pejović, Momčilo M.; Spasić, Ivana V.; Pejović, Milić M.; Nešić, Nikola T.; Brajović, Dragan V.; Brajović

    2013-10-01

    The processes responsible for initiation of electrical breakdown in xenon-filled tube with two spherical iron electrodes at 2.7-mbar pressure have been analyzed. The analysis is based on the experimental data of electrical breakdown time delay as a function of afterglow period. It is shown that positive ions remaining from previous discharge, as well as positive ions created in mutual collisions of metastable atoms in afterglow, have a dominant role in secondary emission of electrons from the cathode which lead to initiation of breakdown in early afterglow. In late afterglow, dominant role in initiation of breakdown is taken by N(4S) atoms formed during the discharge by dissociation of ground state nitrogen molecules that are present as impurities in xenon. When the concentration of N(4S) atoms decreases sufficiently, the initiation of breakdown is caused by cosmic radiation. Small doses of gamma-ray irradiation also contribute to the initiation of breakdown, but only for large values of the afterglow period.

  4. Study of nitrogen flowing afterglow with mercury vapor injection

    SciTech Connect

    Mazánková, V. Krčma, F.; Trunec, D.

    2014-10-21

    The reaction kinetics in nitrogen flowing afterglow with mercury vapor addition was studied by optical emission spectroscopy. The DC flowing post-discharge in pure nitrogen was created in a quartz tube at the total gas pressure of 1000 Pa and discharge power of 130 W. The mercury vapors were added into the afterglow at the distance of 30 cm behind the active discharge. The optical emission spectra were measured along the flow tube. Three nitrogen spectral systems – the first positive, the second positive, and the first negative, and after the mercury vapor addition also the mercury resonance line at 254 nm in the spectrum of the second order were identified. The measurement of the spatial dependence of mercury line intensity showed very slow decay of its intensity and the decay rate did not depend on the mercury concentration. In order to explain this behavior, a kinetic model for the reaction in afterglow was developed. This model showed that the state Hg(6 {sup 3}P{sub 1}), which is the upper state of mercury UV resonance line at 254 nm, is produced by the excitation transfer from nitrogen N{sub 2}(A{sup 3}Σ{sup +}{sub u}) metastables to mercury atoms. However, the N{sub 2}(A{sup 3}Σ{sup +}{sub u}) metastables are also produced by the reactions following the N atom recombination, and this limits the decay of N{sub 2}(A{sup 3}Σ{sup +}{sub u}) metastable concentration and results in very slow decay of mercury resonance line intensity. It was found that N atoms are the most important particles in this late nitrogen afterglow, their volume recombination starts a chain of reactions which produce excited states of molecular nitrogen. In order to explain the decrease of N atom concentration, it was also necessary to include the surface recombination of N atoms to the model. The surface recombination was considered as a first order reaction and wall recombination probability γ = (1.35 ± 0.04) × 10{sup −6} was determined from the experimental data. Also

  5. Controlled growth of copper oxide nanostructures by atmospheric pressure micro-afterglow

    NASA Astrophysics Data System (ADS)

    Altaweel, A.; Filipič, G.; Gries, T.; Belmonte, T.

    2014-12-01

    A large variety of copper oxide nanostructures encompassing nanodots, nanowires and nanowalls, sometimes organized in “cabbage-like” architectures, are grown locally by direct oxidation of copper thin films using the micro-afterglow of an Ar-O2 microwave plasma operating at atmospheric pressure. Morphology, structure and composition of the oxidized copper thin films are characterized by X-ray diffraction, secondary ion mass spectrometry and scanning electron microscopy. The concentric areas where each kind of nanostructures is found are defined by both their radial position with respect to the afterglow centre and by experimental conditions. A growth mechanism is proposed, based on stress-induced outward migration of copper ions. The development of stress gradients is caused by the formation of a copper oxide scale layer. If copper oxide nanowires can be grown as in thermal oxidation processes, micro-afterglow conditions offer novel nanostructures and nano-architectures.

  6. Machine Learning Search for Gamma-Ray Burst Afterglows in Optical Images

    NASA Astrophysics Data System (ADS)

    Topinka, M.

    2016-06-01

    Thanks to the advances in robotic telescopes, time domain astronomy leads to a large number of transient events detected in images every night. Data mining and machine learning tools used for object classification are presented. The goal is to automatically classify transient events for both further follow-up by a larger telescope and for statistical studies of transient events. Special attention is given to the identification of gamma-ray burst afterglows. Machine learning techniques are used to identify GROND gamma-ray burst afterglow among the astrophysical objects present in the SDSS archival images based on the g'-r', r'-i' and i'-z' color indices. The performance of the support vector machine, random forest and neural network algorithms is compared. A joint meta-classifier, built on top of the individual classifiers, can identify GRB afterglows with the overall accuracy of ≳ 90%.

  7. Spectrophotometric analysis of gamma-ray burst afterglow extinction curves with X-Shooter

    NASA Astrophysics Data System (ADS)

    Japelj, J.; Covino, S.; Gomboc, A.; Vergani, S. D.; Goldoni, P.; Selsing, J.; Cano, Z.; D'Elia, V.; Flores, H.; Fynbo, J. P. U.; Hammer, F.; Hjorth, J.; Jakobsson, P.; Kaper, L.; Kopač, D.; Krühler, T.; Melandri, A.; Piranomonte, S.; Sánchez-Ramírez, R.; Tagliaferri, G.; Tanvir, N. R.; de Ugarte Postigo, A.; Watson, D.; Wijers, R. A. M. J.

    2015-07-01

    We use gamma-ray burst (GRB) afterglow spectra observed with the VLT/X-Shooter spectrograph to measure rest-frame extinction in GRB lines-of-sight by modelling the broadband near-infrared (NIR) to X-ray afterglow spectral energy distributions (SEDs). Our sample consists of nine Swift GRBs, of which eight belong to the long-duration and one to the short-duration class. Dust is modelled using the average extinction curves of the Milky Way and the two Magellanic Clouds. We derive the rest-frame extinction of the entire sample, which fall in the range 0 ≲ AV ≲ 1.2. Moreover, the SMC extinction curve is the preferred extinction curve template for the majority of our sample, a result that is in agreement with those commonly observed in GRB lines of sights. In one analysed case (GRB 120119A), the common extinction curve templates fail to reproduce the observed extinction. To illustrate the advantage of using the high-quality, X-Shooter afterglow SEDs over the photometric SEDs, we repeat the modelling using the broadband SEDs with the NIR-to-UV photometric measurements instead of the spectra. The main result is that the spectroscopic data, thanks to a combination of excellent resolution and coverage of the blue part of the SED, are more successful in constraining extinction curves and therefore dust properties in GRB hosts with respect to photometric measurements. In all cases but one the extinction curve of one template is preferred over the others. We show that themodelled values of the extinction AV and the spectral slope, obtained through spectroscopic and photometric SED analysis, can differ significantly for individual events, though no apparent trend in the differences is observed. Finally we stress that, regardless of the resolution of the optical-to-NIR data, the SED modelling gives reliable results only when the fit is performed on a SED covering a broader spectral region (in our case extending to X-rays). Based on observations collected at the European

  8. The prompt-early afterglow connection in gamma-ray bursts: implications for the early afterglow physics

    NASA Astrophysics Data System (ADS)

    Hascoët, R.; Daigne, F.; Mochkovitch, R.

    2014-07-01

    The early X-ray afterglow of gamma-ray bursts revealed by Swift carried many surprises. Following an initial steep decay the light curve often exhibits a plateau phase that can last up to several 104 s, with in addition the presence of flares in 50 per cent of the cases. We focus in this paper on the plateau phase whose origin remains highly debated. We confront several newly discovered correlations between prompt and afterglow quantities (isotropic emitted energy in gamma-rays, luminosity and duration of the plateau) to several models proposed for the origin of plateaus in order to check if they can account for these observed correlations. We first show that the scenario of plateau formation by energy injection into the forward shock leads to an efficiency crisis for the prompt phase and therefore study two possible alternatives: the first one still takes place within the framework of the standard forward shock model but allows for a variation of the microphysics parameters to reduce the radiative efficiency at early times; in the second scenario the early afterglow results from a long-lived reverse shock. Its shape then depends on the distribution of energy as a function of Lorentz factor in the ejecta. In both cases, we first present simple analytical estimates of the plateau luminosity and duration and then compute detailed light curves. In the two considered scenarios we find that plateaus following the observed correlations can be obtained under the condition that specific additional ingredients are included. In the forward shock scenario, the preferred model supposes a wind external medium and a microphysics parameter ɛe that first varies as n-ξ (n being the external density), with ξ ˜ 1 to get a flat plateau, before staying constant below a critical density n0. To produce a plateau in the reverse shock scenario the ejecta must contain a tail of low Lorentz factor with a peak of energy deposition at Γ ≳ 10.

  9. Advances in flowing afterglow and selected-ion flow tube techniques

    NASA Astrophysics Data System (ADS)

    Squires, Robert R.

    1992-09-01

    New developments in flowing afterglow and selected-ion flow tube (SIFT) techniques are briefly reviewed. Particular emphasis is given to the new chemical and physical information that can be obtained with use of the tandem flowing afterglow-triple quadrupole apparatus developed in the author's laboratory. Several outstanding recent achievements in the design and utilization of flowing afterglow and SIFT instruments in other laboratories are briefly highlighted that illustrate the power and flexibility of flow-tube-based methods. These include isotope tracer experiments with the tandem flowing afterglow-SIFT instrument in Boulder, studies of large molecular cluster ions with the variable temperature facility at Penn State, and gas-phase metal ion reactions with the laser ablation/fast flow reactor in Madison. Recent applications of the flowing afterglow-triple quadrupole instrument in our laboratory have made use of collision-induced dissociation (CID) as a tool for synthesizing novel ions and for obtaining new thermo-chemical information from threshold energy measurements. Collision-induced decar☐ylation of organic car☐ylate ions provides access to a variety of unusual and highly basic carbanions that cannot be generated with conventional ion sources. The formation and properties of saturated alkyl ions and studies of gas-phase reactions of the methyl anion are briefly described. We have developed a new method for carrying out "preparative CID" in a flowing afterglow with use of a mini-drift tube; some recent applications of this new ion source are presented. Measurement of CID thresholds for simple cleavage reactions of thermalized ions can provide accurate measures of bond strengths, gas-phase acidities and basicities, and heats of formation for ions and reactive neutral species. Applications of this approach in the thermochemical characterization of carbenes, benzynes and biradicals are described. Future prospects for the continued development of flow

  10. The behaviour of negative oxygen ions in the afterglow of a reactive HiPIMS discharge

    NASA Astrophysics Data System (ADS)

    Bowes, M.; Bradley, J. W.

    2014-07-01

    Using a single Langmuir probe, the temporal evolution of the oxygen negative ion, n-, and electron, ne, densities in the afterglow of a reactive HiPIMS discharge operating in argon-oxygen gas mixtures have been determined. The magnetron was equipped with a titanium target and operated in ‘poisoned’ mode at a frequency of 100 Hz with a pulse width of 100 µs for a range of oxygen partial pressures, {p_{O_{2}}}/{p_{total}} = 0.0{{-}}0.5 . In the initial afterglow, the density of the principle negative ion in the discharge (O-) was of the order of 1016 m-3 for all conditions. The O- concentration was found to decay slowly with characteristic decay times between 585 µs and 1.2 ms over the oxygen partial pressure range. Electron densities were observed to fall more rapidly, resulting in long-lived highly electronegative afterglow plasmas where the ratio, α = n-/ne, was found to reach values up to 672 (±100) for the highest O2 partial pressure. By comparing results to a simple plasma-chemical model, we speculate that with increased {p_{O_{2}}}/{p_{total}} ratio, more O- ions are formed in the afterglow via dissociative electron attachment to highly excited metastable oxygen molecules, with the latter being formed during the active phase of the discharge. After approximately 2.5 ms into the off-time, the afterglow degenerates into an ion-ion plasma and negative ions are free to impinge upon the chamber walls and grounded substrates with flux densities of the order of 1018 m-2 s-1, which is around 10% of the positive ion flux measured during the on-time. This illustrates the potential importance of the long afterglow in reactive HiPIMS, which can act as a steady source of low energy O- ions to a growing thin film at the substrate during periods of reduced positive ion bombardment.

  11. Polymer etching in the oxygen afterglow - Increased etch rates with increased reactor loading

    NASA Technical Reports Server (NTRS)

    Lerner, N. R.; Wydeven, T.

    1989-01-01

    Reactor loading has an effect on the etch rate (rate of decrease of film thickness) of films of polyvinylfluoride (Tedlar) and polyethylene exposed in the afterglow of an RF discharge in oxygen. The etch rate is found to increase with the total surface area of the polymer exposed in the reactor. The etch rates of polypyromellitimide (Kapton H) and polystyrene under these conditions are very low. However, the etch rate of these polymers is greatly enhanced by adding either Tedlar or polyethylene to the reactor. A kinetic model is proposed based on the premise that the oxygen atoms produced by the RF discharge react with Tedlar or polyethylene to produce a much more reactive species, which dominates the etching of the polymers studied.

  12. The properties of a novel green long afterglow phosphor Zn2GeO4:Mn2+, Pr3+

    NASA Astrophysics Data System (ADS)

    Wan, Minhua; Wang, Yinhai; Wang, Xiansheng; Zhao, Hui; Hu, Zhengfa

    2014-01-01

    Novel Zn2GeO4:Mn2+, Pr3+ long afterglow phosphor was successfully synthesized by the high temperature solid state reaction. Long afterglow properties of the sample has been investigated in detail by measuring the X-ray diffraction (XRD), excitation spectrum, emission spectrum, afterglow spectrum, decay curve and thermoluminescence curve. The X-ray diffraction phases indicate that the co-doped Mn2+, Pr3+ have little influence on the crystal structure of Zn2GeO4. According to the emission spectra, we found that the Zn2GeO4:Mn2+, Pr3+ exhibit a narrow band emission with the peak at 532 nm, which could be ascribed to Mn2+ transition between 4T1 and 6A1 electron configurations. The green long afterglow of Zn2GeO4:Mn2+, Pr3+ could be observed for three hours by naked eyes at room temperature under 254 nm UV excitation. The thermoluminescence (TL) curve is employed for the discussion of the origin of the traps and the mechanism of the persistent luminescence. The results suggest that Zn2GeO4 may be an excellent host material for Mn2+-based long afterglow. Furthermore, the function of co-doped Pr3+ ions is confirmed as trap center, which can greatly postpone the afterglow emission properties of Mn2+.

  13. GRB 070125 and the environments of spectral-line poor afterglow absorbers

    NASA Astrophysics Data System (ADS)

    De Cia, A.; Starling, R. L. C.; Wiersema, K.; van der Horst, A. J.; Vreeswijk, P. M.; Björnsson, G.; de Ugarte Postigo, A.; Jakobsson, P.; Levan, A. J.; Rol, E.; Schulze, S.; Tanvir, N. R.

    2011-11-01

    GRB 070125 is among the most energetic bursts detected and the most extensively observed so far. Nevertheless, unresolved issues are still open in the literature on the physics of the afterglow and on the gamma-ray burst (GRB) environment. In particular, GRB 070125 was claimed to have exploded in a galactic halo environment, based on the uniqueness of the optical spectrum and the non-detection of an underlying host galaxy. In this work we collect all publicly available data and address these issues by modelling the near-infrared to X-ray spectral energy distribution (SED) and studying the high signal-to-noise ratio Very Large Telescope/FOcal Reducer/low dispersion Spectrograph afterglow spectrum in comparison with a larger sample of GRB absorbers. The SED reveals a synchrotron cooling break in the ultraviolet, low equivalent hydrogen column density and little reddening caused by a Large Magellanic Cloud type or Small Magellanic Cloud type extinction curve. From the weak Mg II absorption at z= 1.5477 in the spectrum, we derived log N(Mg II) = 12.96+0.13- 0.18 and upper limits on the ionic column density of several metals. These suggest that the GRB absorber is most likely a Lyman limit system with a 0.03 < Z < 1.3 Z⊙ metallicity. The comparison with other GRB absorbers places GRB 070125 at the low end of the absorption-line equivalent width distribution, confirming that weak spectral features and spectral-line poor absorbers are not so uncommon in afterglow spectra. Moreover, we show that the effect of photoionization on the gas surrounding the GRB, combined with a low N(H I) along a short segment of the line of sight within the host galaxy, can explain the lack of spectral features in GRB 070125. Finally, the non-detection of an underlying galaxy is consistent with a faint GRB host galaxy, well within the GRB host brightness distribution. Thus, the possibility that GRB 070125 is simply located in the outskirts of a gas-rich, massive star-forming region inside its

  14. Ignition and afterglow dynamics of a high pressure nanosecond pulsed helium micro-discharge: II. Rydberg molecules kinetics

    NASA Astrophysics Data System (ADS)

    Carbone, Emile A. D.; Schregel, Christian-Georg; Czarnetzki, Uwe

    2016-10-01

    In this paper, we discuss the experimental results presented in Schregel et al (2016 Plasma Sources Sci. Technol. 25 054003) on a high pressure micro-discharge operated in helium and driven by nanosecond voltage pulses. A simple global plasma chemistry model is developed to describe the ions, excited atomic and molecular species dynamics in the ignition and early afterglow regimes. The existing experimental data on high pressure helium kinetics is reviewed and critically discussed. It is highlighted that several inconsistencies in the branching ratio of neutral assisted associative and dissociative processes currently exist in the literature and need further clarification. The model allows to pinpoint the mechanisms responsible for the large amounts of Rydberg molecules produced in the discharge and for the helium triplet metastable state in the afterglow. The main losses of electrons are also identified. The fast quenching of excited He (n  >  3) states appears to be a significant source of Rydberg molecules which has been previously neglected. The plasma model finally draws a simplified, but still accurate description of high pressure helium discharges based on available experimental data for ion and neutral helium species.

  15. FROM ENGINE TO AFTERGLOW: COLLAPSARS NATURALLY PRODUCE TOP-HEAVY JETS AND EARLY-TIME PLATEAUS IN GAMMA-RAY BURST AFTERGLOWS

    SciTech Connect

    Duffell, Paul C.; MacFadyen, Andrew I. E-mail: macfadyen@nyu.edu

    2015-06-20

    We demonstrate that the steep decay and long plateau in the early phases of gamma-ray burst X-ray afterglows are naturally produced in the collapsar model, by a means ultimately related to the dynamics of relativistic jet propagation through a massive star. We present two-dimensional axisymmetric hydrodynamical simulations that start from a collapsar engine and evolve all the way through the late afterglow phase. The resultant outflow includes a jet core that is highly relativistic after breaking out of the star, but becomes baryon loaded after colliding with a massive outer shell, corresponding to mass from the stellar atmosphere of the progenitor star which became trapped in front of the jet core at breakout. The prompt emission produced before or during this collision would then have the signature of a high Lorentz factor jet, but the afterglow is produced by the amalgamated post-collision ejecta that has more inertia than the original highly relativistic jet core and thus has a delayed deceleration. This naturally explains the early light curve behavior discovered by Swift, including a steep decay and a long plateau, without invoking late-time energy injection from the central engine. The numerical simulation is performed continuously from engine to afterglow, covering a dynamic range of over 10 orders of magnitude in radius. Light curves calculated from the numerical output demonstrate that this mechanism reproduces basic features seen in early afterglow data. Initial steep decays are produced by internal shocks, and the plateau corresponds to the coasting phase of the outflow.

  16. Characterization of the flowing afterglows of an N2 O2 reduced-pressure discharge: setting the operating conditions to achieve a dominant late afterglow and correlating the NOβ UV intensity variation with the N and O atom densities

    NASA Astrophysics Data System (ADS)

    Boudam, M. K.; Saoudi, B.; Moisan, M.; Ricard, A.

    2007-03-01

    The flowing afterglow of an N2-O2 discharge in the 0.6-10 Torr range is examined in the perspective of achieving sterilization of medical devices (MDs) under conditions ensuring maximum UV intensity with minimum damage to polymer-based MDs. The early afterglow is shown to be responsible for creating strong erosion damage, requiring that the sterilizer be operated in a dominant late-afterglow mode. These two types of afterglow can be characterized by optical emission spectroscopy: the early afterglow is distinguished by an intense emission from the N_{2}^{+} 1st negative system (band head at 391.4 nm) while the late afterglow yields an overpopulation of the v' = 11 ro-vibrational level of the N2(B) state, indicating a reduced contribution from the early afterglow N2 metastable species. We have studied the influence of operating conditions (pressure, O2 content in the N2-O2 mixture, distance of the discharge from the entrance to the afterglow (sterilizer) chamber) in order to achieve a dominant late afterglow that also ensures maximum and almost uniform UV intensity in the sterilization chamber. As far as operating conditions are concerned, moving the plasma source sufficiently far from the chamber entrance is shown to be a practical means for significantly reducing the density of the characteristic species of the early afterglow. Using the NO titration method, we obtain the (absolute) densities of N and O atoms in the afterglow at the NO injection inlet, a few cm before the chamber entrance: the N atom density goes through a maximum at approximately 0.3-0.5% O2 and then decreases, while the O atom density increases regularly with the O2 percentage. The spatial variation of the N atom (relative) density in the chamber is obtained by recording the emission intensity from the 1st positive system at 580 nm: in the 2-5 Torr range, this density is quite uniform everywhere in the chamber. The (relative) densities of N and O atoms in the discharge are determined by using

  17. On the Afterglow and Progenitor of FRB 150418

    NASA Astrophysics Data System (ADS)

    Zhang, Bing

    2016-05-01

    Keane et al. recently detected a fading radio source following FRB 150418, leading to the identification of a putative host galaxy at z = 0.492 ± 0.008. Assuming that the fading source is the afterglow of FRB 150418, I model the afterglow and constrain the isotropic energy of the explosion to be a few 1050 erg, comparable to that of a short-duration gamma-ray burst (GRB). The outflow may have a jet opening angle of ˜0.22 rad, so that the beaming-corrected energy is below 1049 erg. The results rule out most fast radio burst (FRB) progenitor models for this FRB, but may be consistent with either of the following two scenarios. The first scenario invokes a merger of an NS-NS binary, which produced an undetected short GRB and a supra-massive neutron star, which subsequently collapsed into a black hole, probably hundreds of seconds after the short GRB. The second scenario invokes a merger of a compact star binary (BH-BH, NS-NS, or BH-NS) system whose pre-merger dynamical magnetospheric activities made the FRB, which is followed by an undetected short GRB-like transient. The gravitational-wave (GW) event GW 150914 would be a sister of FRB 150418 in this second scenario. In both cases, one expects an exciting prospect of GW/FRB/GRB associations.

  18. Perspective on Afterglows: Numerically Computed Views, Light Curves, and the Analysis of Homogeneous and Structured Jets with Lateral Expansion

    NASA Astrophysics Data System (ADS)

    Salmonson, Jay D.

    2003-08-01

    Herein I present numerical calculations of light curves of homogeneous and structured afterglows with various lateral expansion rates as seen from any vantage point. Such calculations allow for direct simulation of observable quantities for complex afterglows with arbitrary energy distributions and lateral expansion paradigms. A simple, causal model is suggested for lateral expansion of the jet as it evolves: namely, that the lateral expansion kinetic energy derives from the forward kinetic energy. As such, the homogeneous jet model shows that lateral expansion is important at all times in the afterglow evolution and that analytical scaling laws do a poor job at describing the afterglow decay before and after the break. In particular, I find that lateral expansion does not cause a break in the light curve as had been predicted. A primary purpose of this paper is to study structured afterglows, which do a good job of reproducing global relationships and correlations in the data and thus suggest the possibility of a universal afterglow model. Simulations of structured jets show a general trend in which jet breaks become more pronounced with increasing viewing angle with respect to the jet axis. In fact, under certain conditions a bump can occur in the light curve at the jet-break time. I derive scaling relations for this bump and suggest that it may be a source of some bumps in observed light curves such as that of GRB 000301C. A couple of lateral expansion models are tested over a range of efficiencies and viewing angles, and it is found that lateral expansion can, in some cases, substantially sharpen the jet break. I show flux surface contour maps and simulated images of the afterglows that give insight into how they evolve and determine their light curves.

  19. CORRELATED SPECTRAL AND TEMPORAL BEHAVIOR OF LATE-TIME AFTERGLOWS OF GAMMA-RAY BURSTS

    SciTech Connect

    Dado, Shlomo; Dar, Arnon

    2012-12-20

    The cannonball (CB) model of gamma-ray bursts (GRBs) predicts that the asymptotic behavior of the spectral energy density of GRB afterglows is a power law in time and in frequency, and the difference between the temporal and spectral power-law indices, {alpha}{sub X} - {beta}{sub X}, is restricted to the values 0, 1/2, and 1. Here we report the distributions of the values {alpha}{sub X} and {beta}{sub X}, and their difference for a sample of 315 Swift GRBs. This sample includes all Swift GRBs that were detected before 2012 August 1, whose X-ray afterglow extended well beyond 1 day and the estimated error in {alpha}{sub X} - {beta}{sub X} was {<=}0.25. The values of {alpha}{sub X} were extracted from the CB-model fits to the entire light curves of their X-ray afterglow while the spectral index was extracted by the Swift team from the time-integrated X-ray afterglow of these GRBs. We found that the distribution of the difference {alpha}{sub X} - {beta}{sub X} for these 315 Swift GRBs has three narrow peaks around 0, 1/2, and 1 whose widths are consistent with being due to the measurement errors, in agreement with the CB-model prediction.

  20. A possible explanation for the radio afterglow of GRB 980519: the dense medium effect

    NASA Astrophysics Data System (ADS)

    Wang, X. Y.; Dai, Z. G.; Lu, T.

    2000-09-01

    GRB 980519 is characterized by its rapidly declining optical and X-ray afterglows. Explanations of this behaviour include models invoking a dense medium environment, which makes the shock wave evolve quickly into the subrelativistic phase, a jet-like outflow, and a wind-shaped circumburst medium environment. Recently, Frail et al. found that the latter two cases are consistent with the radio afterglow of this burst. Here, by considering the transrelativistic shock hydrodynamics, we show that the dense medium model can also account for the radio light curve quite well. The potential virtue of the dense medium model for GRB 980519 is that it implies a smaller angular size of the afterglow, which is essential for interpreting the strong modulation of the radio light curve. Optical extinction arising from the dense medium is not important if the prompt optical-UV flash accompanying the γ-ray emission can destroy dust by sublimation out to an appreciable distance. Comparisons with some other radio afterglows are also discussed.

  1. Rapid UBVRI Follow-up of the Highly Collimated Optical Afterglow of GRB 010222

    NASA Astrophysics Data System (ADS)

    Stanek, Krzysztof Z.; Garnavich, Peter M.; Jha, Saurabh; Kilgard, Roy E.; McDowell, Jonathan C.; Bersier, David; Challis, Peter M.; Falco, Emilio; Quinn, Jason L.

    2001-12-01

    We present the earliest optical observations of the optical counterpart to the gamma-ray burst (GRB) 010222, obtained with the Fred L. Whipple Observatory 1.2 m telescope in UBVRI passbands, starting 3.64 hr after the burst (0.4 hr after public notification of the burst localization). We also present late R-band observations of the afterglow obtained with the 1.8 m Vatican Advanced Technology Telescope ~25 days after the burst. The temporal analysis of our data joined with published data indicates a steepening decay, independent of wavelength, asymptotically approaching Fν~t-0.80+/-0.05 at early times (t<<1 day) and Fν~t-1.30+/-0.05 at late times, with a sharp break at tb=0.72+/-0.10 days. This is the second earliest observed break of any afterglow (after GRB 980519), which clearly indicates the importance of rapid multiband follow-up for GRB afterglow research. The optical spectral energy distribution, corrected for small Galactic reddening, can be fitted fairly well by a single power law with Fν~ν-1.07+/-0.09. However, when we fit using our BVRI data only, we obtain a shallower slope of -0.88+/-0.10, in excellent agreement with the slope derived from our low-resolution spectrum (-0.89+/-0.03). The spectral slope and light-curve decay slopes we derive are not consistent with a jet model despite the presence of a temporal break. Significant host dust extinction with a starburst reddening law would flatten the spectral index to match jet predictions and still be consistent with the observed spectral energy distribution. We derive an opening angle of 2.1d, smaller than any listed in the recent compilation of Frail et al. The total beamed energy corrected for the jet geometry is 4×1050 ergs, very close to the ``standard'' value of 5×1050 ergs found by Frail et al. for a number of other bursts with light-curve breaks. Based on observations collected at the FLWO 1.2 m telescope and the 1.8 m VATT.

  2. Implications of the Early X-Ray Afterglow Light Curves of Swift GRBs

    SciTech Connect

    Granot, Jonathan; Konigl, Arieh; Piran, Tsvi; /Hebrew U.

    2006-01-17

    According to current models, gamma-ray bursts (GRBs) are produced when the energy carried by a relativistic outflow is dissipated and converted into radiation. The efficiency of this process, {epsilon}{sub {gamma}}, is one of the critical factors in any GRB model. The X-ray afterglow light curves of Swift GRBs show an early stage of flattish decay. This has been interpreted as reflecting energy injection. When combined with previous estimates, which have concluded that the kinetic energy of the late ({approx}> 10 hr) afterglow is comparable to the energy emitted in {gamma}-rays, this interpretation implies very high values of {epsilon}{sub {gamma}}, corresponding to {approx}> 90% of the initial energy being converted into {gamma}-rays. Such a high efficiency is hard to reconcile with most models, including in particular the popular internal-shocks model. We re-analyze the derivation of the kinetic energy from the afterglow X-ray flux and re-examine the resulting estimates of the efficiency. We confirm that, if the flattish decay arises from energy injection and the pre-Swift broad-band estimates of the kinetic energy are correct, then {epsilon}{sub {gamma}} {approx}> 0.9. We discuss various issues related to this result, including an alternative interpretation of the light curve in terms of a two-component outflow model, which we apply to the X-ray observations of GRB 050315. We point out, however, that another interpretation of the flattish decay--a variable X-ray afterglow efficiency (e.g., due to a time dependence of afterglow shock microphysical parameters)--is possible. We also show that direct estimates of the kinetic energy from the late X-ray afterglow flux are sensitive to the assumed values of the shock microphysical parameters and suggest that broad-band afterglow fits might have underestimated the kinetic energy (e.g., by overestimating the fraction of electrons that are accelerated to relativistic energies). Either one of these possibilities implies a

  3. The Swift XRT: Observations of Early X-ray Afterglows

    SciTech Connect

    Burrows, David N.; Kennea, J. A.; Nousek, J. A.; Osborne, J. P.; O'Brien, P. T.; Chincarini, G.; Tagliaferri, G.; Giommi, P.; Zhang, B.

    2006-05-19

    During the first year of operations of the Swift observatory, the X-ray Telescope has made a number of discoveries concerning the nature of X-ray afterglows of both long and short GRBs. We highlight the key findings, which include rapid declines at early times, a standard template of afterglow light curve shapes, common flaring, and the discovery of the first short GRB afterglow.

  4. The X-ray afterglows of Gamma-Ray Bursts

    NASA Astrophysics Data System (ADS)

    Watson, D.

    2014-07-01

    Gamma-ray bursts are renowned for being the brightest explosions since the Big Bang. They are extremely useful probes with which to study the cosmos, primarily because of their bright afterglows. While the afterglow is panchromatic, the X-ray afterglow has proved extremely useful: the first localisations of both short and long-duration GRBs were made via their X-ray afterglows, an X-ray afterglow is associated with almost every burst, and spectroscopy of the X-ray afterglow informs us of the material close to the GRB as well as providing an unobscured measurement of the afterglow flux for virtually every GRB. We now have an incredibly rich database of ten years worth of GRBs and their afterglows from the Swift satellite, where its rapid autonomous repointing has allowed its X-Ray Telescope to be on target only minutes after the GRB. Here I will review what we have learnt from the X-ray afterglows of GRBs and describe some exciting recent results.

  5. Gamma ray burst outflows and afterglows

    NASA Astrophysics Data System (ADS)

    Morsony, Brian J.

    2008-08-01

    We carry out a theoretical investigation of jet propagation in Gamma Ray Bursts and examine the jitter radiation mechanism as a means of producing prompt and afterglow emission. We study the long-term evolution of relativistic jets in collapsars and examine the effects of viewing angle on the subsequent gamma ray bursts. Our simulations allow us to single out three phases in the jet evolution: a precursor phase in which relativistic material turbulently shed from the head of the jet first emerges from the star; a shocked jet phase where a fully shocked jet of material is emerging; and an unshocked jet phase where the jet consists of a free-streaming, unshocked core surrounded by a thin boundary layer of shocked jet material. We also carry out a series of simulations with central engines that vary on long time periods comparable to the breakout time of the jet, on short time periods (0.1s) much less than the breakout time, and finally that decay as a power law at late times. We conclude that rapid variability seen in prompt GRB emission, as well as shallow decays and flares seen in the X-ray afterglow, can be caused by central engine variability. Finally, we present a detailed computation of the jitter radiation spectrum, including self-absorption, for electrons inside Weibel-like shock- generated magnetic fields. We apply our results to the case of the prompt and afterglow emission of gamma-ray bursts. We conclude that jitter and synchrotron afterglows can be distinguished from each other with good quality observations. However, it is unlikely that the difference can explain the peculiar behavior of several recent observations, such as flat X-ray slopes and uncorrelated optical and X-ray behavior.

  6. GAMMA-RAY BURST DYNAMICS AND AFTERGLOW RADIATION FROM ADAPTIVE MESH REFINEMENT, SPECIAL RELATIVISTIC HYDRODYNAMIC SIMULATIONS

    SciTech Connect

    De Colle, Fabio; Ramirez-Ruiz, Enrico; Granot, Jonathan; Lopez-Camara, Diego

    2012-02-20

    We report on the development of Mezcal-SRHD, a new adaptive mesh refinement, special relativistic hydrodynamics (SRHD) code, developed with the aim of studying the highly relativistic flows in gamma-ray burst sources. The SRHD equations are solved using finite-volume conservative solvers, with second-order interpolation in space and time. The correct implementation of the algorithms is verified by one-dimensional (1D) and multi-dimensional tests. The code is then applied to study the propagation of 1D spherical impulsive blast waves expanding in a stratified medium with {rho}{proportional_to}r{sup -k}, bridging between the relativistic and Newtonian phases (which are described by the Blandford-McKee and Sedov-Taylor self-similar solutions, respectively), as well as to a two-dimensional (2D) cylindrically symmetric impulsive jet propagating in a constant density medium. It is shown that the deceleration to nonrelativistic speeds in one dimension occurs on scales significantly larger than the Sedov length. This transition is further delayed with respect to the Sedov length as the degree of stratification of the ambient medium is increased. This result, together with the scaling of position, Lorentz factor, and the shock velocity as a function of time and shock radius, is explained here using a simple analytical model based on energy conservation. The method used for calculating the afterglow radiation by post-processing the results of the simulations is described in detail. The light curves computed using the results of 1D numerical simulations during the relativistic stage correctly reproduce those calculated assuming the self-similar Blandford-McKee solution for the evolution of the flow. The jet dynamics from our 2D simulations and the resulting afterglow light curves, including the jet break, are in good agreement with those presented in previous works. Finally, we show how the details of the dynamics critically depend on properly resolving the structure of the

  7. Gamma-Ray Burst Dynamics and Afterglow Radiation from Adaptive Mesh Refinement, Special Relativistic Hydrodynamic Simulations

    NASA Astrophysics Data System (ADS)

    De Colle, Fabio; Granot, Jonathan; López-Cámara, Diego; Ramirez-Ruiz, Enrico

    2012-02-01

    We report on the development of Mezcal-SRHD, a new adaptive mesh refinement, special relativistic hydrodynamics (SRHD) code, developed with the aim of studying the highly relativistic flows in gamma-ray burst sources. The SRHD equations are solved using finite-volume conservative solvers, with second-order interpolation in space and time. The correct implementation of the algorithms is verified by one-dimensional (1D) and multi-dimensional tests. The code is then applied to study the propagation of 1D spherical impulsive blast waves expanding in a stratified medium with ρvpropr -k , bridging between the relativistic and Newtonian phases (which are described by the Blandford-McKee and Sedov-Taylor self-similar solutions, respectively), as well as to a two-dimensional (2D) cylindrically symmetric impulsive jet propagating in a constant density medium. It is shown that the deceleration to nonrelativistic speeds in one dimension occurs on scales significantly larger than the Sedov length. This transition is further delayed with respect to the Sedov length as the degree of stratification of the ambient medium is increased. This result, together with the scaling of position, Lorentz factor, and the shock velocity as a function of time and shock radius, is explained here using a simple analytical model based on energy conservation. The method used for calculating the afterglow radiation by post-processing the results of the simulations is described in detail. The light curves computed using the results of 1D numerical simulations during the relativistic stage correctly reproduce those calculated assuming the self-similar Blandford-McKee solution for the evolution of the flow. The jet dynamics from our 2D simulations and the resulting afterglow light curves, including the jet break, are in good agreement with those presented in previous works. Finally, we show how the details of the dynamics critically depend on properly resolving the structure of the relativistic flow.

  8. The Late-time Afterglow of the Extremely Energetic Short Burst GRB 090510 Revisited

    NASA Technical Reports Server (NTRS)

    Guelbenzu, A. Nicuesa; Klose, S.; Kruehler, T.; Greiner, J.; Rossi, A.; Kann, D. A.; Olivares, F.; Rau, A.; Afonso, P. M. J.; Elliott, J.; Filgas, R.; Yoldas, A. Kuepcue; McBreen, S.; Nardini, M.; Schady, P.; Schmidl, S.; Sudilovsky, V.; Updike, A. C.; Yoldas, A.

    2012-01-01

    Context. The Swift discovery of the short burst GRB 090510 has raised considerable attention mainly because of two reasons: first, it had a bright optical afterglow, and second it is among the most energetic events detected so far within the entire GRB population (long plus short). The afterglow of GRB 090510 was observed with Swift/UVOT and Swift/XRT and evidence of a jet break around 1.5 ks after the burst has been reported in the literature, implying that after this break the optical and X-ray light curve should fade with the same decay slope. Aims. As noted by several authors, the post-break decay slope seen in the UVOT data is much shallower than the steep decay in the X-ray band, pointing to a (theoretically hard to understand) excess of optical flux at late times. We assess here the validity of this peculiar behavior. Methods. We reduced and analyzed new afterglow light-curve data obtained with the multichannel imager GROND. These additional g'r'i'z' data were then combined with the UVOT and XRT data to study the behavior of the afterglow at late times more stringently. Results. Based on the densely sampled data set obtained with GROND, we find that the optical afterglow of GRB 090510 did indeed enter a steep decay phase starting around 22 ks after the burst. During this time the GROND optical light curve is achromatic, and its slope is identical to the slope of the X-ray data. In combination with the UVOT data this implies that a second break must have occurred in the optical light curve around 22 ks post burst, which, however, has no obvious counterpart in the X-ray band, contradicting the interpretation that this could be another jet break. Conclusions. The GROND data provide the missing piece of evidence that the optical afterglow of GRB 090510 did follow a post-jet break evolution at late times. The break seen in the optical light curve around 22 ks in combination with its missing counterpart in the X-ray band could be due to the passage of the

  9. Afterglows from the largest explosions in the universe

    PubMed Central

    Hartmann, Dieter H.

    1999-01-01

    The distinction of “largest explosions in the universe” has been bestowed on cosmic gamma-ray bursts. Their afterglows are brighter than supernovae and therefore are called hypernovae. Photometry and spectroscopy of these afterglows have provided major breakthroughs in our understanding of this mysterious phenomenon. PMID:10220364

  10. Energy Injection in Gamma-Ray Burst Afterglows

    NASA Astrophysics Data System (ADS)

    Laskar, Tanmoy; Berger, Edo; Margutti, Raffaella; Perley, Daniel; Zauderer, B. Ashley; Sari, Re'em; Fong, Wen-fai

    2015-11-01

    We present multi-wavelength observations and modeling of gamma-ray bursts (GRBs) that exhibit a simultaneous re-brightening in their X-ray and optical light curves, and are also detected at radio wavelengths. We show that the re-brightening episodes can be modeled by injection of energy into the blastwave and that in all cases the energy injection rate falls within the theoretical bounds expected for a distribution of energy with ejecta Lorentz factor. Our measured values of the circumburst density, jet opening angle, and beaming-corrected kinetic energy are consistent with the distribution of these parameters for long-duration GRBs at both z˜ 1 and z≳ 6, suggesting that the jet launching mechanism and environment of these events are similar to that of GRBs that do not have bumps in their light curves. However, events exhibiting re-brightening episodes have lower radiative efficiencies than average, suggesting that a majority of the kinetic energy of the outflow is carried by slow-moving ejecta, which is further supported by steep measured distributions of the ejecta energy as a function of Lorentz factor. We do not find evidence for reverse shocks over the energy injection period, implying that the onset of energy injection is a gentle process. We further show that GRBs exhibiting simultaneous X-ray and optical re-brightenings are likely the tail of a distribution of events with varying rates of energy injection, forming the most extreme events in their class. Future X-ray observations of GRB afterglows with Swift and its successors will thus likely discover several more such events, while radio follow-up and multi-wavelength modeling of similar events will unveil the role of energy injection in GRB afterglows.

  11. Residual dust charges in discharge afterglow

    SciTech Connect

    Coueedel, L.; Mikikian, M.; Boufendi, L.; Samarian, A. A.

    2006-08-15

    An on-ground measurement of dust-particle residual charges in the afterglow of a dusty plasma was performed in a rf discharge. An upward thermophoretic force was used to balance the gravitational force. It was found that positively charged, negatively charged, and neutral dust particles coexisted for more than 1 min after the discharge was switched off. The mean residual charge for 200-nm-radius particles was measured. The dust particle mean charge is about -5e at a pressure of 1.2 mbar and about -3e at a pressure of 0.4 mbar.

  12. Pink splash of active nitrogen in the discharge afterglow

    SciTech Connect

    Akishev, Yu. S.; Grushin, M. E.; Karal'nik, V. B.; Petryakov, A. V.; Trushkin, N. I.

    2007-09-15

    Results are presented from experimental studies of the glow dynamics of active nitrogen in the stage of its excitation by a current pulse and during the discharge afterglow. The mechanism is proposed for the generation of a light splash in a highly activated nitrogen after the end of its pulsed excitation. The key role in the generation of this splash is played by the D-V processes, by which the dissociation energy is transferred to the vibrational degrees of freedom in the course of recombination of nitrogen atoms, and the V-E processes, by which the vibrational energy of highly excited molecules N{sub 2}(X, v {>=} 25-27) is transferred to the emitting electronic states N{sub 2}(B, v) after the V-V delay. Results of simulations based on the mechanism proposed are also presented.

  13. Afterglow Observations Shed New Light on the Nature of X-ray Flashes

    SciTech Connect

    Granot, J

    2005-02-17

    X-ray flashes (XRFs) and X-ray rich gamma-ray bursts (XRGRBs) share many observational characteristics with long duration ({approx}> 2 s) GRBs, but the reason for which the spectral energy distribution of their prompt emission peaks at lower photon energies, E{sub p}, is still a subject of debate. Although many different models have been invoked in order to explain the lower values of E{sub p}, their implications for the afterglow emission were not considered in most cases, mainly because observations of XRF afterglows have become available only recently. Here we examine the predictions of the various XRF models for the afterglow emission, and test them against the observations of XRF 030723 and XRGRB 041006, the events with the best monitored afterglow light curves in their respective class. We show that most existing XRF models are hard to reconcile with the observed afterglow light curves, which are very flat at early times. Such light curves are, however, naturally produced by a roughly uniform jet with relatively sharp edges that is viewed off-axis (i.e. from outside of the jet aperture). This type of model self consistently accommodates both the observed prompt emission and the afterglow light curves of XRGRB 041006 and XRF 030723, implying viewing angles {theta}{sub obs} from the jet axis of ({theta}{sub obs}-{theta}{sub 0}) {approx} 0.15 {theta}{sub 0} and ({theta}{sub obs}-{theta}{sub 0}) {approx} {theta}{sub 0}, respectively, where {theta}{sub 0} {approx} 3{sup o} is the half-opening angle of the jet. This suggests that GRBs, XRGRBs and XRFs are intrinsically similar relativistic jets viewed from different angles. It is then natural to identify GRBs with {gamma}({theta}{sub obs} - {theta}{sub 0}) {approx}< 1, XRGRBs with 1 {approx}< ({theta}{sub obs} - {theta}{sub 0}) {approx}< a few, and XRFs with {gamma}({theta}{sub obs} - {theta}{sub 0}) {approx}> a few, where {gamma} is the Lorentz factor of the outflow near the edge of the jet from which most of the

  14. Rydberg state, metastable, and electron dynamics in the low-pressure argon afterglow

    NASA Astrophysics Data System (ADS)

    Tsankov, Tsanko V.; Johnsen, Rainer; Czarnetzki, Uwe

    2015-12-01

    In this work a time-dependent collisional-radiative model for recombining plasmas is developed. It tracks the collisional and radiative capture of electrons into highly-excited (Rydberg) states and their consecutive deexcitation through collisions and radiation to the ground or the metastable state. The model allows the calculation of the net recombination rate and the electron energy gain by recombination. It is coupled to the volume-averaged balance equations for the electron density and temperature. The numerical solution of these equations includes a model for the diffusion cooling of the electrons (Celik et al 2012 Phys. Rev. E 85 046407) and a simplified model for the gas cooling. Using as only input the experimentally determined initial values of the electron density and temperature, gas temperature and metastable density, the temporal evolution of all parameters in the afterglow is calculated and compared with measurements. The results reproduce very well the measured quantities (electron density, light emission and metastable density) without the need to invoke adjustable parameters. This gives confidence in the validity of the model that allows it to be used not only to deepen the understanding of afterglow plasmas but also to tailor their properties as required for applications. The analysis of the model results further shows that gas heating and cooling must be explicitly taken into account to reproduce experimental observations. The electron heating by recombination is another process that is important for the good agreement. Both of these effects were largely ignored in previous works on afterglows.

  15. Energies of GRB blast waves and prompt efficiencies as implied by modelling of X-ray and GeV afterglows

    NASA Astrophysics Data System (ADS)

    Beniamini, Paz; Nava, Lara; Duran, Rodolfo Barniol; Piran, Tsvi

    2015-11-01

    We consider a sample of 10 gamma-ray bursts with long-lasting ( ≳ 102 s) emission detected by Fermi/Large Area Telescope and for which X-ray data around 1 d are also available. We assume that both the X-rays and the GeV emission are produced by electrons accelerated at the external forward shock, and show that the X-ray and the GeV fluxes lead to very different estimates of the initial kinetic energy of the blast wave. The energy estimated from GeV is on average ˜50 times larger than the one estimated from X-rays. We model the data (accounting also for optical detections around 1 d, if available) to unveil the reason for this discrepancy and find that good modelling within the forward shock model is always possible and leads to two possibilities: (i) either the X-ray emitting electrons (unlike the GeV emitting electrons) are in the slow-cooling regime or (ii) the X-ray synchrotron flux is strongly suppressed by Compton cooling, whereas, due to the Klein-Nishina suppression, this effect is much smaller at GeV energies. In both cases the X-ray flux is no longer a robust proxy for the blast wave kinetic energy. On average, both cases require weak magnetic fields (10-6 ≲ ɛB ≲ 10-3) and relatively large isotropic kinetic blast wave energies 10^{53} erg<{E}_{0,kin}<10^{55} erg corresponding to large lower limits on the collimated energies, in the range 10^{52} erg<{E}_{θ ,kin}<5× 10^{52} erg for an ISM (interstellar medium) environment with n ˜ 1 cm-3 and 10^{52} erg<{E}_{θ ,kin}<10^{53} erg for a wind environment with A* ˜ 1. These energies are larger than those estimated from the X-ray flux alone, and imply smaller inferred values of the prompt efficiency mechanism, reducing the efficiency requirements on the still uncertain mechanism responsible for prompt emission.

  16. THE PROPERTIES OF THE 2175 A EXTINCTION FEATURE DISCOVERED IN GRB AFTERGLOWS

    SciTech Connect

    Zafar, Tayyaba; Watson, Darach; Eliasdottir, Ardis; Fynbo, Johan P. U.; Kruehler, Thomas; Leloudas, Giorgos; Schady, Patricia; Greiner, Jochen; Jakobsson, Pall; Thoene, Christina C.; Perley, Daniel A.; Morgan, Adam N.; Bloom, Joshua E-mail: darach@dark-cosmology.dk

    2012-07-01

    The unequivocal, spectroscopic detection of the 2175 A bump in extinction curves outside the Local Group is rare. To date, the properties of the bump have been examined in only two gamma-ray burst (GRB) afterglows (GRB 070802 and GRB 080607). In this work, we analyze in detail the detections of the 2175 Angstrom-Sign extinction bump in the optical spectra of two further GRB afterglows: GRB 080605 and 080805. We gather all available optical/near-infrared photometric, spectroscopic, and X-ray data to construct multi-epoch spectral energy distributions (SEDs) for both GRB afterglows. We fit the SEDs with the Fitzpatrick and Massa model with a single or broken power law. We also fit a sample of 38 GRB afterglows, known to prefer a Small Magellanic Cloud (SMC)-type extinction curve, with the same model. We find that the SEDs of GRB 080605 and GRB 080805 at two epochs are fit well with a single power law with a derived extinction of A{sub V} = 0.52{sup +0.13}{sub -0.16} and 0.50{sup +0.13}{sub -0.10}, and 2.1{sup +0.7}{sub -0.6} and 1.5 {+-} 0.2, respectively. While the slope of the extinction curve of GRB 080805 is not well constrained, the extinction curve of GRB 080605 has an unusual very steep far-UV rise together with the 2175 A bump. Such an extinction curve has previously been found in only a small handful of sightlines in the Milky Way. One possible explanation of such an extinction curve may be dust arising from two different regions with two separate grain populations, however we cannot distinguish the origin of the curve. We finally compare the four 2175 A bump sightlines to the larger GRB afterglow sample and to Local Group sightlines. We find that while the width and central positions of the bumps are consistent with what is observed in the Local Group, the relative strength of the detected bump (A{sub bump}) for GRB afterglows is weaker for a given A{sub V} than for almost any Local Group sightline. Such dilution of the bump strength may offer tentative

  17. Physical Processes Shaping Gamma-Ray Burst X-Ray Afterglow Light Curves: Theoretical Implications from the Swift X-Ray Telescope Observations

    NASA Astrophysics Data System (ADS)

    Zhang, Bing; Fan, Y. Z.; Dyks, Jaroslaw; Kobayashi, Shiho; Mészáros, Peter; Burrows, David N.; Nousek, John A.; Gehrels, Neil

    2006-05-01

    With the successful launch of the Swift Gamma-Ray Burst Explorer, a rich trove of early X-ray afterglow data has been collected by its onboard X-Ray Telescope (XRT). Some interesting features are emerging, including a distinct rapidly decaying component preceding the conventional afterglow component in many sources, a shallow decay component before the more ``normal'' decay component observed in a good fraction of GRBs, and X-ray flares in nearly half of the afterglows. In this paper we systematically analyze the possible physical processes that shape the properties of the early X-ray afterglow light curves and use the data to constrain various models. We suggest that the steep decay component is consistent with the tail emission of the prompt gamma-ray bursts and/or the X-ray flares. This provides strong evidence that the prompt emission and afterglow emission are likely two distinct components, supporting the internal origin of the GRB prompt emission. The shallow decay segment observed in a group of GRBs suggests that very likely the forward shock keeps being refreshed for some time. This might be caused by either a long-lived central engine, or a wide distribution of the shell Lorentz factors, or else possibly the deceleration of a Poynting flux-dominated flow. X-ray flares suggest that the GRB central engine is very likely still active after the prompt gamma-ray emission is over, but with a reduced activity at later times. In some cases, the central engine activity even extends to days after the burst triggers. Analyses of early X-ray afterglow data reveal that GRBs are indeed highly relativistic events and that early afterglow data of many bursts, starting from the beginning of the XRT observations, are consistent with the afterglow emission from an ISM environment.

  18. IN SEARCH OF PROGENITORS FOR SUPERNOVALESS GAMMA-RAY BURSTS 060505 AND 060614: RE-EXAMINATION OF THEIR AFTERGLOWS

    SciTech Connect

    Xu, D.; Fynbo, J. P. U.; Sollerman, J.; Watson, D.; Hjorth, J.; Starling, R. L. C.; O'Brien, P. T.; Yost, S.; Foley, S.

    2009-05-01

    GRB 060505 and GRB 060614 are nearby long-duration gamma-ray bursts (LGRBs) without accompanying supernovae (SNe) down to very strict limits. They thereby challenge the conventional LGRB-SN connection and naturally give rise to the question: are there other peculiar features in their afterglows which would help shed light on their progenitors? To answer this question, we combine new observational data with published data and investigate the multiband temporal and spectral properties of the two afterglows. We find that both afterglows can be well interpreted within the framework of the jetted standard external shock wave model, and that the afterglow parameters for both bursts fall well within the range observed for other LGRBs. Hence, from the properties of the afterglows there is nothing to suggest that these bursts should have another progenitor than other LGRBs. Recently, Swift-discovered GRB 080503 also has the spike + tail structure during its prompt {gamma}-ray emission seemingly similar to GRB 060614. We analyze the prompt emission of this burst and find that this GRB is actually a hard-spike + hard-tail burst with a spectral lag of 0.8 {+-} 0.4 s during its tail emission. Thus, the properties of the prompt emission of GRB 060614 and GRB 080503 are clearly different, motivating further thinking of GRB classification (and even identification of faint core-collapse SNe). Finally, we note that, whereas the progenitor of the two SN-less bursts remains uncertain, the core-collapse origin for the SN-less bursts would be quite certain if a windlike environment can be observationally established, e.g., from an optical decay faster than the X-ray decay in the afterglow's slow cooling phase.

  19. Detailed optical and near-infrared polarimetry, spectroscopy and broad-band photometry of the afterglow of GRB 091018: polarization evolution

    NASA Astrophysics Data System (ADS)

    Wiersema, K.; Curran, P. A.; Krühler, T.; Melandri, A.; Rol, E.; Starling, R. L. C.; Tanvir, N. R.; van der Horst, A. J.; Covino, S.; Fynbo, J. P. U.; Goldoni, P.; Gorosabel, J.; Hjorth, J.; Klose, S.; Mundell, C. G.; O'Brien, P. T.; Palazzi, E.; Wijers, R. A. M. J.; D'Elia, V.; Evans, P. A.; Filgas, R.; Gomboc, A.; Greiner, J.; Guidorzi, C.; Kaper, L.; Kobayashi, S.; Kouveliotou, C.; Levan, A. J.; Rossi, A.; Rowlinson, A.; Steele, I. A.; de Ugarte Postigo, A.; Vergani, S. D.

    2012-10-01

    Follow-up observations of large numbers of gamma-ray burst (GRB) afterglows, facilitated by the Swift satellite, have produced a large sample of spectral energy distributions and light curves, from which their basic micro- and macro-physical parameters can in principle be derived. However, a number of phenomena have been observed that defy explanation by simple versions of the standard fireball model, leading to a variety of new models. Polarimetry can be a major independent diagnostic of afterglow physics, probing the magnetic field properties and internal structure of the GRB jets. In this paper we present the first high-quality multi-night polarimetric light curve of a Swift GRB afterglow, aimed at providing a well-calibrated data set of a typical afterglow to serve as a benchmark system for modelling afterglow polarization behaviour. In particular, our data set of the afterglow of GRB 091018 (at redshift z = 0.971) comprises optical linear polarimetry (R band, 0.13-2.3 d after burst); circular polarimetry (R band) and near-infrared linear polarimetry (Ks band). We add to that high-quality optical and near-infrared broad-band light curves and spectral energy distributions as well as afterglow spectroscopy. The linear polarization varies between 0 and 3 per cent, with both long and short time-scale variability visible. We find an achromatic break in the afterglow light curve, which corresponds to features in the polarimetric curve. We find that the data can be reproduced by jet break models only if an additional polarized component of unknown nature is present in the polarimetric curve. We probe the ordered magnetic field component in the afterglow through our deep circular polarimetry, finding Pcirc < 0.15 per cent (2σ), the deepest limit yet for a GRB afterglow, suggesting ordered fields are weak, if at all present. Our simultaneous R- and Ks-band polarimetry shows that dust-induced polarization in the host galaxy is likely negligible.

  20. VLBI AND ARCHIVAL VLA AND WSRT OBSERVATIONS OF THE GRB 030329 RADIO AFTERGLOW

    SciTech Connect

    Mesler, Robert A.; Pihlstroem, Ylva M.; Taylor, Greg B.; Granot, Johnathan

    2012-11-01

    We present VLBI and archival Karl G. Jansky Very Large Array (VLA) and Westerbork Synthesis Radio Telescope (WSRT) observations of the radio afterglow from the gamma-ray burst (GRB) of 2003 March 29 (GRB 030329) taken between 672 and 2032 days after the burst. The VLA and WSRT data suggest a simple power-law decay in the flux at 5 GHz, with no clear signature of any rebrightening from the counterjet. We report an unresolved source at day 2032 of size 1.18 {+-} 0.13 mas, which we use in conjunction with the expansion rate of the burst to argue for the presence of a uniform, interstellar-medium-like circumburst medium. A limit of <0.067 mas yr{sup -1} is placed on the proper motion, supporting the standard afterglow model for gamma-ray bursts.

  1. On the Electron Energy Distribution Index of Swift Gamma-ray Burst Afterglows

    NASA Astrophysics Data System (ADS)

    Curran, P. A.; Evans, P. A.; de Pasquale, M.; Page, M. J.; van der Horst, A. J.

    2010-06-01

    The electron energy distribution index, p, is a fundamental parameter of the synchrotron emission from a range of astronomical sources. Here we examine one such source of synchrotron emission, gamma-ray burst (GRB) afterglows observed by the Swift satellite. Within the framework of the blast wave model, we examine the constraints placed on the distribution of p by the observed X-ray spectral indices and parameterize the distribution. We find that the observed distribution of spectral indices are inconsistent with an underlying distribution of p composed of a single discrete value but consistent with a Gaussian distribution centered at p = 2.36 and having a width of 0.59. Furthermore, accepting that the underlying distribution is a Gaussian, we find that the majority (gsim94%) of GRB afterglows in our sample have cooling break frequencies less than the X-ray frequency.

  2. On the afterglow and host galaxy of GRB 021004: A comprehensivestudy with the Hubble Space Telescope1

    SciTech Connect

    Fynbo, J.P.U.; Gorosabel, J.; Smette, A.; Fruchter, A.; Hjorth,J.; Pedersen, K.; Levan, A.; Burud, I.; Sahu, K.; Vreeswijk, P.M.; Bergeron, E.; Kouveliotou1, C.; Tanvir, N.; Thorsett11, S.E.; Wijers,R.A.M.J.; Castro Ceron, J.M.; Castro-Tirado, A.; Garnavich, P.; Holland,S.T.; Jakobsson, P.; Moller, P.; Nugent, P.; Pian, E.; Rhoads, J.; Thomsen, B.; Watson, D.; Woosley, S.

    2004-12-01

    We report on Hubble Space Telescope (HST) observations of the late-time afterglow and host galaxy of GRB 021004 (z = 2.33).Although this gamma-ray burst (GRB) is one of the best observed so far in terms of sampling in the time domain, multi-wavelength coverage and polarimetric observations, there is large disagreement between different measurements and interpretations of this burst in the literature. We have observed the field of GRB 021004 with the HST at multiple epochs from 3 days until almost 10 months after the burst. With STI S prism and G430L spectroscopy we cover the spectral region from about 2000 Angstrom to 5700 Angstrom corresponding to 600 1700 Angstrom in the rest frame. From the limit on the flux recovery bluewards of the Lyman-limit we constrain the H I column density to be above 1 x 1018 cm-2 (5 sigma). Based on ACS and N ICMOS imaging we find that the afterglow evolved a chromatically within the errors (any variation must be less then 5 percent) during the period of HST observations. The color changes observed by other authors during the first four days must be related to a 'noisy' phenomenon superimposed on an afterglow component with a constant spectral shape. This also means that the cooling break has remained on the blue side of the optical part of the spectrum for at least two weeks after the explosion. The optical to X-ray slope OX is consistent with being the same at 1.4 and 52.4 days after the burst. This indicates that the cooling frequency is constant and hence, according to fireball models, that the circumburst medium has a constant density profile. The late-time slope of the light curve (alpha 2, F nu proportional to t-alpha2) is in the range 2 = 1.8-1.9, although inconsistent with a single power-law. This could be due to a late-time flattening caused by the transition to non-relativistic expansion or due to excess emission (a 'bump' in the light curve) about 7 days afterburst. The host galaxy is like most previously studied GRB hosts

  3. Erosion of a-C:H in the afterglow of ammonia plasma

    NASA Astrophysics Data System (ADS)

    Drenik, Aleksander; Mourkas, Angelos; Zaplotnik, Rok; Primc, Gregor; Mozetič, Miran; Panjan, Peter; Alegre, Daniel; Tabarés, Francisco L.

    2016-07-01

    Amorphous hydrogenated carbon (a-C:H) deposits were eroded in the afterglow of a NH3 plasma, created with an inductively coupled RF generator in pure NH3 at the gas pressure of 50 Pa. The plasma system was characterised by optical emission spectroscopy and mass spectrometry, and the erosion process was monitored in-situ with a laser interferometry system. Based on the mass spectrometry measurements, the degree of dissociation of the NH3 molecules was estimated at 90% at the highest generator forward power in the discharge region, however the densities of N and H atoms were significantly smaller at the location of the sample holder. The erosion rates were found to increase with surface temperature and forward generator power. In the high dissociation regime, the composition of the afterglow and the reaction products highlight the role of N atoms in the erosion process.

  4. MULTI-WAVELENGTH AFTERGLOWS OF FAST RADIO BURSTS

    SciTech Connect

    Yi, Shuang-Xi; Gao, He; Zhang, Bing

    2014-09-01

    The physical origin of fast radio bursts (FRBs) is unknown. Detecting electromagnetic counterparts to FRBs in other wavelengths is essential to measure their distances and to determine their physical origin. Assuming that at least some of them are of cosmological origin, we calculate their afterglow light curves in multiple wavelengths (X-rays, optical, and radio) by assuming a range of total kinetic energies and redshifts. We focus on forward shock emission, but also consider the possibility that some of the FRBs might have bright reverse shock emission. In general, FRB afterglows are too faint to be detected by current detectors. Only if an FRB has a very low radiative efficiency in radio (hence, a very large kinetic energy), and when it is close enough to observe can its afterglow be detected in the optical and radio bands. We discuss observational strategies for detecting these faint afterglows using future telescopes such as Large Synoptic Survey Telescope and Expanded Very Large Array.

  5. The afterglow of GRB 130427A from 1 to 10{sup 16} GHz

    SciTech Connect

    Perley, D. A.; Cenko, S. B.; Corsi, A.; Tanvir, N. R.; Wiersema, K.; Levan, A. J.; Kann, D. A.; Greiner, J.; Sonbas, E.; Zheng, W.; Clubb, K. I.; Zhao, X.-H.; Bai, J.-M.; Chang, L.; Bremer, M.; Castro-Tirado, A. J.; Fruchter, A.; Göğüş, E.; Güver, T.; and others

    2014-01-20

    We present multiwavelength observations of the afterglow of GRB 130427A, the brightest (in total fluence) gamma-ray burst (GRB) of the past 29 yr. Optical spectroscopy from Gemini-North reveals the redshift of the GRB to be z = 0.340, indicating that its unprecedented brightness is primarily the result of its relatively close proximity to Earth; the intrinsic luminosities of both the GRB and its afterglow are not extreme in comparison to other bright GRBs. We present a large suite of multiwavelength observations spanning from 300 s to 130 days after the burst and demonstrate that the afterglow shows relatively simple, smooth evolution at all frequencies, with no significant late-time flaring or rebrightening activity. The entire data set from 1 GHz to 10 GeV can be modeled as synchrotron emission from a combination of reverse and forward shocks in good agreement with the standard afterglow model, providing strong support to the applicability of the underlying theory and clarifying the nature of the GeV emission observed to last for minutes to hours following other very bright GRBs. A tenuous, wind-stratified circumburst density profile is required by the observations, suggesting a massive-star progenitor with a low mass-loss rate, perhaps due to low metallicity. GRBs similar in nature to GRB 130427A, inhabiting low-density media and exhibiting strong reverse shocks, are probably not uncommon but may have been difficult to recognize in the past owing to their relatively faint late-time radio emission; more such events should be found in abundance by the new generation of sensitive radio and millimeter instruments.

  6. Phenomenology of reverse-shock emission in the optical afterglows of gamma-ray bursts

    SciTech Connect

    Japelj, J.; Kopač, D.; Gomboc, A.; Kobayashi, S.; Harrison, R.; Virgili, F. J.; Mundell, C. G.; Guidorzi, C.; Melandri, A. E-mail: andreja.gomboc@fmf.uni-lj.si

    2014-04-20

    We use a parent sample of 118 gamma-ray burst (GRB) afterglows, with known redshift and host galaxy extinction, to separate afterglows with and without signatures of dominant reverse-shock (RS) emission and to determine which physical conditions lead to a prominent reverse-shock emission. We identify 10 GRBs with reverse-shock signatures: 990123, 021004, 021211, 060908, 061126, 080319B, 081007, 090102, 090424, and 130427A. By modeling their optical afterglows with reverse- and forward-shock analytic light curves and using Monte Carlo simulations, we estimate the parameter space of the physical quantities describing the ejecta and circumburst medium. We find that physical properties cover a wide parameter space and do not seem to cluster around any preferential values. Comparing the rest-frame optical, X-ray, and high-energy properties of the larger sample of non-RS-dominated GRBs, we show that the early-time (<1 ks) optical spectral luminosity, X-ray afterglow luminosity, and γ-ray energy output of our reverse-shock dominated sample do not differ significantly from the general population at early times. However, the GRBs with dominant reverse-shock emission have fainter than average optical forward-shock emission at late times (>10 ks). We find that GRBs with an identifiable reverse-shock component show a high magnetization parameter R {sub B} = ε{sub B,r}/ε{sub B,f} ∼ 2-10{sup 4}. Our results are in agreement with the mildly magnetized baryonic jet model of GRBs.

  7. Extremely Soft X-Ray Flash as the Indicator of Off-axis Orphan GRB Afterglow

    NASA Astrophysics Data System (ADS)

    Urata, Yuji; Huang, Kuiyun; Yamazaki, Ryo; Sakamoto, Takanori

    2015-06-01

    We verified the off-axis jet model of X-ray flashes (XRFs) and examined a discovery of off-axis orphan gamma-ray burst (GRB) afterglows. The XRF sample was selected on the basis of the following three factors: (1) a constraint on the lower peak energy of the prompt spectrum {E}{obs}{src}, (2) redshift measurements, and (3) multicolor observations of an earlier (or brightening) phase. XRF 020903 was the only sample selected on the basis of these criteria. A complete optical multicolor afterglow light curve of XRF 020903 obtained from archived data and photometric results in the literature showed an achromatic brightening around 0.7 days. An off-axis jet model with a large observing angle (0.21 rad, which is twice the jet opening half-angle, {θ }{jet}) can naturally describe the achromatic brightening and the prompt X-ray spectral properties. This result indicates the existence of off-axis orphan GRB afterglow light curves. Events with a larger viewing angle (\\gt ∼ 2{θ }{jet}) could be discovered using an 8 m class telescope with wide-field imagers such as the Subaru Hyper-Suprime-Cam and the Large Synoptic Survey Telescope.

  8. Signature of a Spin-up Magnetar from Multi-band Afterglow Rebrightening of GRB 100814A

    NASA Astrophysics Data System (ADS)

    Yu, Y. B.; Huang, Y. F.; Wu, X. F.; Xu, M.; Geng, J. J.

    2015-06-01

    In recent years, more and more gamma-ray bursts (GRBs) with late rebrightenings in their multi-band afterglows have revealed the late-time activity of their central engines. GRB 100814A is a special case among the well-sampled events, with complex temporal and spectral evolution. The single power-law shallow decay index of the optical light curve observed by GROND between 640 s and 10 ks is {{α }opt}=0.57+/- 0.02, which apparently conflicts with expectations from the simple external shock model. In particular, there is remarkable rebrightening in the optical to near-infrared bands at late times, challenging the external shock model with synchrotron emission coming from the interaction of the blast wave with the surrounding interstellar medium. In this paper, we invoke a magnetar with spin evolution to explain the complex multi-band afterglow emission of GRB 100814A. The initial shallow decay phase in the optical bands and the plateau in the X-ray can be explained as being due to energy injection from a spin-down magnetar. At late times, with materials from the fall-back disk falling onto the central object of the burster, the angular momentum of the accreted materials is transferred to the magnetar, which leads to a spin up process. As a result, the magnetic dipole radiation luminosity will increase, resulting in significant rebrightening of the optical afterglow. We show that the model can well reproduce the observed multi-band afterglow emission.

  9. Evolution of dust content in galaxies probed by gamma-ray burst afterglows

    NASA Astrophysics Data System (ADS)

    Kuo, Tzu-Ming; Hirashita, Hiroyuki; Zafar, Tayyaba

    2013-12-01

    Because of their brightness, gamma-ray burst (GRB) afterglows are viable targets for investigating the dust content in their host galaxies. Simple intrinsic spectral shapes of GRB afterglows allow us to derive the dust extinction. Recently, the extinction data of GRB afterglows are compiled up to redshift z = 6.3, in combination with hydrogen column densities and metallicities. This data set enables us to investigate the relation between dust-to-gas ratio and metallicity out to high redshift for a wide metallicity range. By applying our evolution models of dust content in galaxies, we find that the dust-to-gas ratios derived from GRB afterglow extinction data are excessively high such that they can be explained with a fraction of gas-phase metals condensed into dust (fin) ˜ 1, while theoretical calculations on dust formation in the wind of asymptotic giant branch stars and in the ejecta of Type II supernovae suggest a much more moderate condensation efficiency (fin ˜ 0.1). Efficient dust growth in dense clouds has difficulty in explaining the excessive dust-to-gas ratio at metallicities Z/Z⊙ < ɛ, where ɛ is the star formation efficiency of the dense clouds. However, if ɛ is as small as 0.01, the dust-to-gas ratio at Z ˜ 10-2 Z⊙ can be explained with nH ≳ 106 cm-3. Therefore, a dense environment hosting dust growth is required to explain the large fraction of metals condensed into dust, but such clouds should have low star formation efficiencies to avoid rapid metal enrichment by stars.

  10. Imprints of Electron-Positron Winds on the Multiwavelength Afterglows of Gamma-ray Bursts

    NASA Astrophysics Data System (ADS)

    Geng, J. J.; Wu, X. F.; Huang, Y. F.; Li, L.; Dai, Z. G.

    2016-07-01

    Optical rebrightenings in the afterglows of some gamma-ray bursts (GRBs) are unexpected within the framework of the simple external shock model. While it has been suggested that the central engines of some GRBs are newly born magnetars, we aim to relate the behaviors of magnetars to the optical rebrightenings. A newly born magnetar will lose its rotational energy in the form of Poynting-flux, which may be converted into a wind of electron-positron pairs through some magnetic dissipation processes. As proposed by Dai, this wind will catch up with the GRB outflow and a long-lasting reverse shock (RS) would form. By applying this scenario to GRB afterglows, we find that the RS propagating back into the electron-positron wind can lead to an observable optical rebrightening and a simultaneous X-ray plateau (or X-ray shallow decay). In our study, we select four GRBs (i.e., GRB 080413B, GRB 090426, GRB 091029, and GRB 100814A), of which the optical afterglows are well observed and show clear rebrightenings. We find that they can be well interpreted. In our scenario, the spin-down timescale of the magnetar should be slightly smaller than the peak time of the rebrightening, which can provide a clue to the characteristics of the magnetar.

  11. Understanding the Flowing Atmospheric-Pressure Afterglow (FAPA) Ambient Ionization Source through Optical Means

    NASA Astrophysics Data System (ADS)

    Shelley, Jacob T.; Chan, George C.-Y.; Hieftje, Gary M.

    2012-02-01

    The advent of ambient desorption/ionization mass spectrometry (ADI-MS) has led to the development of a large number of atmospheric-pressure ionization sources. The largest group of such sources is based on electrical discharges; yet, the desorption and ionization processes that they employ remain largely uncharacterized. Here, the atmospheric-pressure glow discharge (APGD) and afterglow of a helium flowing atmospheric-pressure afterglow (FAPA) ionization source were examined by optical emission spectroscopy. Spatial emission profiles of species created in the APGD and afterglow were recorded under a variety of operating conditions, including discharge current, electrode polarity, and plasma-gas flow rate. From these studies, it was found that an appreciable amount of atmospheric H2O vapor, N2, and O2 diffuses through the hole in the plate electrode into the discharge to become a major source of reagent ions in ADI-MS analyses. Spatially resolved plasma parameters, such as OH rotational temperature (Trot) and electron number density (ne), were also measured in the APGD. Maximum values for Trot and ne were found to be ~1100 K and ~4 × 1019 m-3, respectively, and were both located at the pin cathode. In the afterglow, rotational temperatures from OH and N{2/+} yielded drastically different values, with OH temperatures matching those obtained from infrared thermography measurements. The higher N{2/+} temperature is believed to be caused by charge-transfer ionization of N2 by He{2/+}. These findings are discussed in the context of previously reported ADI-MS analyses with the FAPA source.

  12. Determination of Cosmological Parameters from GRB Correlation between E_iso (gamma) and Afterglow Flux

    NASA Astrophysics Data System (ADS)

    Hannachi, Zitouni; Guessoum, Nidhal; Azzam, Walid

    2016-07-01

    Context: We use the correlation relations between the energy emitted by the GRBs in their prompt phases and the X-ray afterglow fluxes, in an effort to constrain cosmological parameters and construct a Hubble diagram at high redshifts, i.e. beyond those found in Type Ia supernovae. Methods: We use a sample of 128 Swift GRBs, which we have selected among more than 800 ones observed until July 2015. The selection is based on a few observational constraints: GRB flux higher than 0.4 photons/cm^2/s in the band 15-150 keV; spectrum fitted with simple power law; redshift accurately known and given; and X-ray afterglow observed and flux measured. The statistical method of maximum likelihood is then used to determine the best cosmological parameters (Ω_M, Ω_L) that give the best correlation between the isotropic gamma energies E_{iso} and the afterglow fluxes at the break time t_{b}. The χ^2 statistical test is also used as a way to compare results from two methods. Results & Conclusions: Although the number of GRBs with high redshifts is rather small, and despite the notable dispersion found in the data, the results we have obtained are quite encouraging and promising. The values of the cosmological parameters obtained here are close to those currently used.

  13. ON THE FORMATION OF Lyalpha EMISSION FROM RESONANTLY SCATTERED CONTINUUM PHOTONS OF GAMMA-RAY BURST's AFTERGLOW

    SciTech Connect

    Xu Wen; Wu Xiangping

    2010-02-20

    The continuum spectrum of gamma-ray burst's (GRB) afterglow at Lyalpha wavelength is known to be otherwise featureless except for the existence of a pair of smooth damping wings. Resonant scattering of photons with the ambient neutral hydrogen around the GRB may alter this picture. We study the formation and evolution of the spectral imprint of these resonantly scattered photons in the context of GRB's afterglow. Based on an analytic model that includes photons that are scattered only once, as well as a complete treatment of all the scatterings using Monte Carlo simulations, we are able to calculate the spectrum and luminosity of this Lyalpha emission from a very early moment up to a late epoch. We find that the amount, the motion, and the geometry of the neutral hydrogen around the GRB, together with the time behavior of the source are the crucial factors that affect the predicted luminosity and spectral profile. The flux of the Lyalpha emission is found to be mainly contributed by photons that are scattered only once. The flux is of the order 10{sup -4}-10{sup -9} relative to the undecayed maximum flux of the transmitted continuum, making the feature negligible but potentially observable. If not obscured by the host galaxy's damped Lyalpha absorption systems or intergalactic neutral hydrogen, the feature may appear sometime from 1 hr to several years when the directly transmitted light has faded away. This scattered emission feature can be distinguished from Lyalpha photons of other origins by its luminosity evolution and by its gradual narrowing of profile with time. The typical timescale for spectral variance is that of the light crossing time of a hydrogen clump close to the GRB. If observed, the resonant peaks' time-dependent behavior is a scanning probe on the distribution of neutral hydrogen in GRB's immediate neighborhood.

  14. Investigation on luminescence enhancement and decay characteristics of long afterglow nanophosphors for dark-vision display applications

    NASA Astrophysics Data System (ADS)

    Swati, G.; Chawla, S.; Mishra, S.; Rajesh, B.; Vijayan, N.; Sivaiah, B.; Dhar, A.; Haranath, D.

    2015-04-01

    Long afterglow SrAl2O4:Eu2+,Dy3+ nanophosphors were synthesized via a facile but effectual auto-combustion technique followed by post-annealing treatment at elevated temperatures. The influence of various fuels during synthesis and thereafter improvement in the luminescence decay characteristics under various illuminant irradiations of long afterglow nanophosphors have been reported. Extensive studies on structural, morphological and luminescent properties of the as-synthesized afterglow nanophosphors have been presented. Powder X-ray diffraction studies confirm the presence of high-purity, single-phase monoclinic nanophosphors. HRTEM investigations confirm the formation of nanophosphors of particle size less than 50 nm. Photoluminescence emission is attributed to the characteristic d-f transition (4f65d1→4f7) of Eu2+ ions and was positioned at 512 nm. As-synthesized nanophosphors exhibit considerable confinement effects resulting into blue shift in emission maxima as compared to their bulk counterparts. The mechanism underlined for long afterglow has been discussed using trapping-detrapping model. The nanophosphor being multifunctional finds many interesting applications including dark-vision display, energy storage, fingerprint detection, in vivo and in vitro biological staining, etc.

  15. GRB 020410: A Gamma-ray burst afterglow discovered by its supernova light

    SciTech Connect

    Levan, Andrew; Nugent, Peter; Fruchter, Andrew; Burud, Ingunn; Branch, David; Rhoads, James; Castro-Tirado, Alberto; Gorosabel, Javier; Ceron, Jose Maria Castro; Thorsett, Stephen E.; Kouveliotou, Chryssa; Golenetskii, Sergey; Fynbo, Johan; Garnavich, Peter; Holland, Stephen; Hjorth, Jens; Moller, Palle; Pian, Elena; Tanvir, Nial; Ulanov, Mihail; Wijers, Ralph; Woosley, Stan

    2004-03-19

    We present the discovery and monitoring of the optical transient (OT) associated with GRB 020410. The fading OT was found by Hubble Space Telescope (HST) observations taken 28 and 65 days after burst at a position consistent with the X-ray afterglow. Subsequent re-examination of early ground based observations revealed that a faint OT was present 6 hours after burst, confirming the source association with GRB 020410. A deep non-detection after one week requires that the OT re-brightened between day 7 and day 28, and further late time HST data taken approximately 100 days after burst imply that it is very red (F{sub nu} proportional to nu-2.7). We compare both the flux and color of the excess with supernova models and show that the data are best explained by the presence of a Type I b/c supernova at a redshift z approx. equal 0.5, which occurred roughly coincident with the day of GRB.

  16. Gamma-Ray Bursts: The Afterglow Revolution

    NASA Astrophysics Data System (ADS)

    Galama, Titus J.; Sari, Re'em

    GRBs were discovered with the Vela satellites, whose main purpose was to verify compliance with the 1963 Limited Nuclear Test Ban Treaty. Since their discovery these events, which emit the bulk of their energy in the 0.1 - 1.0 MeV range, and whose durations span milliseconds to tens of minutes, posed one of the great unsolved problems in astrophysics. GRBs are formed in extreme relativistic outflows and provide important information about highly relativistic acceleration mechanisms. Until 1997, no counterparts (quiescent as well as transient) could be found and observations did not provide a direct measurement of their distance. The breakthrough came in early 1997, when the Wide Field Cameras aboard the Italian-Dutch BeppoSAX satellite allowed rapid and accurate localization of GRBs. Follow-up on these positions resulted in the discovery of X-ray, optical and radio afterglows. These observations revealed that GRBs come from 'cosmological' distances, and that they are by far the most luminous photon sources in the Universe, with peak luminosities in γ rays up to 1052 erg/s, and total energy budgets up to several times 1053-54 erg (for assumed isotropic emission). Evidence is accumulating, however, that GRB outflow is collimated in the form of jets and when corrected for the geometry of the outflow the energies of GRBs appear to cluster around 5 x 1050 ergs- very comparable to that of supernovae. GRBs are rare phenomena with an overall rate about 2000 times smaller than that of supernovae. Indirect evidence in the last several years shows that a fraction of GRBs may be related to a peculiar type of supernova explosions. Theoretical work has shown that these supernovae most likely mark the birth events of stellar mass black holes as the final products of the evolution of very massive stars. A fundamental question is whether there are also other processes that can drive such an engine, for example the coalescence of a double neutron-star system. Finally, the

  17. Electrical characterization of the flowing afterglow of N{sub 2} and N{sub 2}/O{sub 2} microwave plasmas at reduced pressure

    SciTech Connect

    Afonso Ferreira, J.; Stafford, L. Leonelli, R.; Ricard, A.

    2014-04-28

    A cylindrical Langmuir probe was used to analyze the spatial distribution of the number density of positive ions and electrons as well as the electron energy distribution function (EEDF) in the flowing afterglow of a 6 Torr N{sub 2} and N{sub 2}/O{sub 2} plasma sustained by a propagating electromagnetic surface wave in the microwave regime. In pure N{sub 2} discharges, ion densities were in the mid 10{sup 14} m{sup −3} in the pink afterglow and in the mid 10{sup 12} m{sup −3} early in the late afterglow. In both pink and late afterglows, the ion population was much higher than the electron population, indicating non-macroscopically neutral media. The EEDF was close to a Maxwellian with an electron temperature of 0.5 ± 0.1 eV, except in the pink afterglow where the temperature rose to 1.1 ± 0.2 eV. This latter behavior is ascribed to N{sub 2} vibration-vibration pumping in the pink afterglow that increases the concentration of high N{sub 2} vibrational states and thus rises the electron temperature by vibration-electron collisions. After addition of small amounts of O{sub 2} in the nominally pure N{sub 2} discharge, the charged particles densities and average electron energy first strongly increased and then decreased with increasing O{sub 2} concentration. Based on these data and the evolution of the N{sub 2}{sup +}(B) band emission intensities, it is concluded that a significant change in the positive ion composition of the flowing afterglow occurs, going from N{sub 2}{sup +} in nominally pure N{sub 2} discharges to NO{sup +} after addition of trace amounts of O{sub 2} in N{sub 2}.

  18. Radio rebrightening of the GRB afterglow by the accompanying supernova

    NASA Astrophysics Data System (ADS)

    Barniol Duran, R.; Giannios, D.

    2015-12-01

    The gamma-ray burst (GRB) jet powers the afterglow emission by shocking the surrounding medium, and radio afterglow can now be routinely observed to almost a year after the explosion. Long-duration GRBs are accompanied by supernovae (SNe) that typically contain much more energy than the GRB jet. Here we consider the fact that the SN blast wave will also produce its own afterglow (supernova remnant emission), which will peak at much later time (since it is non-relativistic), when the SN blast wave transitions from a coasting phase to a decelerating Sedov-Taylor phase. We predict that this component will peak generally a few tens of years after the explosion and it will outshine the GRB powered afterglow well-before its peak emission. In the case of GRB 030329, where the external density is constrained by the ˜10-year coverage of the radio GRB afterglow, the radio emission is predicted to start rising over the next decade and to continue to increase for the following decades up to a level of ˜ mJy. Detection of the SN-powered radio emission will greatly advance our knowledge of particle acceleration in ˜0.1c shocks.

  19. On the Afterglow and Host Galaxy of GRB 021004: A Comprehensive Study with the Hubble Space Telescope

    NASA Astrophysics Data System (ADS)

    Fynbo, J. P. U.; Gorosabel, J.; Smette, A.; Fruchter, A.; Hjorth, J.; Pedersen, K.; Levan, A.; Burud, I.; Sahu, K.; Vreeswijk, P. M.; Bergeron, E.; Kouveliotou, C.; Tanvir, N.; Thorsett, S. E.; Wijers, R. A. M. J.; Castro Cerón, J. M.; Castro-Tirado, A.; Garnavich, P.; Holland, S. T.; Jakobsson, P.; Møller, P.; Nugent, P.; Pian, E.; Rhoads, J.; Thomsen, B.; Watson, D.; Woosley, S.

    2005-11-01

    We report on Hubble Space Telescope (HST) observations of the late-time afterglow and host galaxy of GRB 021004 (z=2.33). Although this gamma-ray burst (GRB) is one of the best observed so far in terms of sampling in the time domain, multiwavelength coverage, and polarimetric observations, there is substantial disagreement between different interpretations of data sets on this burst in the literature. We have observed the field of GRB 021004 with the HST at multiple epochs from 3 days until almost 10 months after the burst. With the STIS PRISM and G430L spectroscopy, we cover the spectral region from about 2000 to 5700 Å, corresponding to 600-1700 Å in the rest frame. From the limit on the flux recovery blueward of the Lyman limit, we constrain the H I column density to be above 1×1018 cm-2 (5 σ). On the basis of ACS and NICMOS imaging, we find that the afterglow evolved achromatically within the errors (any variation must be less than 5%) during the period of the HST observations. The color changes observed by other authors during the first 4 days must be related to a stochastic phenomenon superimposed on an afterglow component with a constant spectral shape. This achromaticity implies that the cooling break has remained on the blue side of the optical part of the spectrum for at least 2 weeks after the explosion. The optical-to-X-ray slope βOX is consistent with being the same at 1.4 and 52.4 days after the burst. This indicates that the cooling frequency is constant and, hence, according to fireball models, that the circumburst medium has a constant density profile. The late-time slope of the light curve (α2, Fν~t-α2) is in the range α2=1.8-1.9 and is inconsistent with a single power law. This could be due to a late-time flattening caused by the transition to nonrelativistic expansion or could be due to excess emission (a ``bump'' in the light curve) about 7 days after the burst. The host galaxy is, like most previously studied GRB hosts, a (very) blue

  20. Probing a Gamma-Ray Burst Progenitor at a Redshift of z = 2: A Comprehensive Observing Campaign Campaign of the Afterglow of GRB 030226

    NASA Technical Reports Server (NTRS)

    Klose, S.; Greiner, J.; Rau, A.; Henden, A. A.; Hartmann, D. H.; Zeh, A.; Ries, C.; Masetti, N.; Malesani, D.; Guenther, E.

    2004-01-01

    We report results from a comprehensive follow-up observing campaign of the afterglow of GRB 030226 including VLT spectroscopy, VLT polarimetry, and Chandra X-ray observations. In addition, we present BOOTES-1 wide-field observations at the time of the occurrence of the burst. First observations at ESO started 0.2 days after the event when the gamma ray burst (GRB) afterglow was at a magnitude of R approximately 19 and continued until the afterglow had faded below the detection threshold (R greater than 26). No underlying host galaxy was found. The optical light curve shows a break around 0.8 days after the burst, which is achromatic within the observational errors, supporting the view that it was due to a jetted explosion. Close to the break time the degree of linear polarization of the afterglow light was less than 1.1%, which favors a uniform-jet model rather than a structured one. VLT spectra show two absorption line systems at redshifts z = 1.962 plus or minus 0.001 and 1.986 plus or minus 0.001, placing the lower limit for the redshift of the GRB close to 2. We emphasize that the kinematics and the composition of the absorbing clouds responsible for these line systems are very similar to those observed in the afterglow of GRB 021004. This corroborates the picture in which at least some GRBs are physically related to the explosion of a Wolf-Rayet star.

  1. Green chemistry-mediated synthesis of nanostructures of afterglow phosphor

    NASA Astrophysics Data System (ADS)

    Sharma, Pooja; Haranath, D.; Chander, Harish; Singh, Sukhvir

    2008-04-01

    Various nanostructures of SrAl 2O 4:Eu 2+, Dy 3+ (SAC) afterglow phosphor were prepared in a single-step reaction using a green chemistry-mediated modified combustion process. The evolution of hazardous NxOx gases during the customary combustion reaction was completely eliminated by employing an innovative complex formation route. Another fascinating feature of the process was that, a slight change in the processing conditions ensured the synthesis of either nanoparticles or nanowires. The photoluminescence spectrum of nanophosphor showed a slight blue shift in emission (˜511 nm) as compared to the bulk phosphor (˜520 nm). The afterglow (decay) profiles of SAC nanoparticles, nanowires and bulk phosphor were compared. The chemistry underlying the nanostructure synthesis and the probable afterglow mechanism were discussed.

  2. Altitudinal dependence of meteor radio afterglows measured via optical counterparts

    NASA Astrophysics Data System (ADS)

    Obenberger, K. S.; Holmes, J. M.; Dowell, J. D.; Schinzel, F. K.; Stovall, K.; Sutton, E. K.; Taylor, G. B.

    2016-09-01

    Utilizing the all-sky imaging capabilities of the first station of the Long Wavelength Array along with a host of all-sky optical cameras, we have now observed 44 optical meteor counterparts to radio afterglows. Combining these observations, we have determined the geographic positions of all 44 afterglows. Comparing the number of radio detections as a function of altitude above sea level to the number of expected bright meteors, we find a strong altitudinal dependence characterized by a cutoff below ˜90 km, below which no radio emission occurs, despite the fact that many of the observed optical meteors penetrated well below this altitude. This cutoff suggests that wave damping from electron collisions is an important factor for the evolution of radio afterglows. This finding agrees with the hypothesis that the emission is the result of electron plasma wave emission.

  3. The origin of the plateau and late rebrightening in the afterglow of GRB 120326A

    SciTech Connect

    Hou, S. J.; Lu, J. F.; Geng, J. J.; Wang, K.; Huang, Y. F.; Dai, Z. G.; Wu, X. F.

    2014-04-20

    GRB 120326A is an unusual gamma-ray burst (GRB) that has a long plateau and a very late rebrightening in both X-ray and optical bands. The similar behavior of the optical and X-ray light curves suggests that they may share a common origin. The long plateau starts at several hundred seconds and ends at tens of thousands of seconds, and the peak time of the late rebrightening is about 30,000 s. We analyze the energy injection model by means of numerical and analytical solutions, considering both the wind environment and the interstellar medium environment for GRB afterglows. We particularly study the influence of the injection starting time, ending time, stellar wind density (or density of the circumburst environment), and injection luminosity on the shape of the afterglow light curves, respectively. In the wind model, we find that the light curve is largely affected by the parameters and that there is a 'bump' in the late stage. In the wind environment, we found that the longer the energy is injected, the more obvious the rebrightening will be. We also find that the peak time of the bump is determined by the stellar wind density. We use the late continuous injection model to interpret the unusual afterglow of GRB 120326A. The model fits the observational data well; however, we find that the timescale of the injection must be higher than 10,000 s, which implies that the timescale of the central engine activity must also be more than 10,000 s. This information can give useful constraints on the central engines of GRBs—we consider a newborn millisecond pulsar with a strong magnetic field to be the central engine. On the other hand, our results suggest that the circumburst environment of GRB 120326A is very likely a stellar wind.

  4. Observational Signatures of High-Energy Emission during the Shallow Decay Phase of Gamma-Ray Burst X-Ray Afterglows

    NASA Astrophysics Data System (ADS)

    Yu, Y. W.; Liu, X. W.; Dai, Z. G.

    2007-12-01

    The widely existing shallow decay phase of the X-ray afterglows of gamma-ray bursts (GRBs) is generally accepted to be due to long-lasting energy injection. The outflows carrying the injecting energy, based on the component that is dominant in energy, fall into two possible types: baryon-dominated and lepton-dominated ones. The former type of outflow could be ejecta that is ejected during the prompt phase of a GRB and consists of a series of baryonic shells with a distribution of Lorentz factors, and the latter type could be an electron-positron pair wind that is driven by the postburst central engine. We here provide a unified description for the dynamics of fireballs based on these two types of energy injection and calculate the corresponding high-energy photon emission by considering synchrotron radiation and inverse Compton scattering (including synchrotron self-Compton and combined inverse Compton) of electrons. We find that, in the two energy-injection models, there is a plateau (even a hump) in high-energy light curves during the X-ray shallow decay phase. In particular, a considerable fraction of the injecting energy in the lepton-dominated model can be shared by the long-lasting reverse shock since it is relativistic. Furthermore, almost all of the energy of the reverse shock is carried by leptons, and thus, the inverse Compton emission is enhanced dramatically. Therefore, this model predicts more significant high-energy afterglow emission than the baryon-dominated model. We argue that these observational signatures would be used to discriminate between different energy-injection models in the upcoming Gamma-Ray Large Area Space Telescope (GLAST) era.

  5. The plateau phase of gamma-ray burst afterglows in the thick-shell scenario

    NASA Astrophysics Data System (ADS)

    Leventis, K.; Wijers, R. A. M. J.; van der Horst, A. J.

    2014-01-01

    We present analytic calculations of synchrotron radiation from the forward and the reverse shock of gamma-ray burst blast waves, in the thick-shell scenario (i.e. when the reverse shock is relativistic). We show that this scenario can naturally account for the plateau phase, observed early in the afterglows of about half the bursts detected by Swift. We generalize our approach to include power-law luminosity of the central engine and show that when radiation from both regions (forward and reverse shock) is taken into account, a wide range of possibilities emerge, including chromatic and achromatic breaks, frequency-dependent spectral evolution during the injection break and widely varying decay indices in different bands. For both the forward and the reverse shock, we derive formulas for the spectral parameters and the observed flux in different power-law segments of the spectrum, as a function of observer time. We explore the Fb-tb relation (between the observed time of the end of the plateau phase and the flux at that point) in the framework of the presented model and show that model predictions favour the reverse shock as the dominant source of emission in both optical and X-rays. As case studies, we present simultaneous fits to X-ray and optical/IR afterglow data of GRB 080928 and GRB 090423. We identify the end of the plateau phase with the cessation of energy injection and infer the corresponding upper limits to central-engine activity, which are about 1 h for the former and 1.5 h for the latter. We conclude that smooth energy injection through the reverse shock is a plausible explanation for the plateau phase of gamma-ray burst afterglows. During that phase, radiation from the reverse shock is likely to be important, or even dominant, and should be taken into account when fitting model parameters to observations.

  6. NuSTAR OBSERVATIONS OF GRB 130427A ESTABLISH A SINGLE COMPONENT SYNCHROTRON AFTERGLOW ORIGIN FOR THE LATE OPTICAL TO MULTI-GEV EMISSION

    SciTech Connect

    Kouveliotou, C.; Racusin, J. L.; Gehrels, N.; McEnery, J. E.; Zhang, W. W.; Bellm, E.; Harrison, F. A.; Vianello, G.; Oates, S.; Fryer, C. L.; Boggs, S. E.; Craig, W. W.; Christensen, F. E.; Dermer, C. D.; Hailey, C. J.; Melandri, A.; Tagliaferri, G.; Mundell, C. G.; Stern, D. K. E-mail: granot@openu.ac.il

    2013-12-10

    GRB 130427A occurred in a relatively nearby galaxy; its prompt emission had the largest GRB fluence ever recorded. The afterglow of GRB 130427A was bright enough for the Nuclear Spectroscopic Telescope ARray (NuSTAR) to observe it in the 3-79 keV energy range long after its prompt emission (∼1.5 and 5 days). This range, where afterglow observations were previously not possible, bridges an important spectral gap. Combined with Swift, Fermi, and ground-based optical data, NuSTAR observations unambiguously establish a single afterglow spectral component from optical to multi-GeV energies a day after the event, which is almost certainly synchrotron radiation. Such an origin of the late-time Fermi/Large Area Telescope >10 GeV photons requires revisions in our understanding of collisionless relativistic shock physics.

  7. Direct and bulk-scattered forward-shock emissions: sources of X-ray afterglow diversity

    SciTech Connect

    Panaitescu, A.

    2008-05-22

    I describe the modifications to the standard forward-shock model required to account for the X-ray light-curve features discovered by Swift in the early afterglow emission and propose that a delayed, pair-enriched, and highly relativistic outflow, which bulk-scatters the forward-shock synchrotron emission, yields sometimes a brighter X-ray emission, producing short-lived X-ray flares, X-ray light-curve plateaus ending with chromatic breaks, and fast post-plateau decays.

  8. Recombination of H3(+) and D3(+) Ions in a Flowing Afterglow Plasma

    NASA Technical Reports Server (NTRS)

    Gougousi, T.; Johnsen, R.; Golde, M. F.

    1995-01-01

    The analysis of flowing afterglow plasmas containing H3(+) or D3(+) ions indicates that the de-ionization of such plasmas does not occur by simple dissociative recombination of ions with electrons. An alternative model of de-ionization is proposed in which electrons are captured into H3(**) auto-ionization Rydberg states that are stabilized by collisional mixing of the Rydberg molecules' angular momenta. The proposed mechanism would enable de-ionization to occur without the need for dissociative recombination by the mechanisms of potential-surface crossings.

  9. Magnetic scavengers as carriers of analytes for flowing atmospheric pressure afterglow mass spectrometry (FAPA-MS).

    PubMed

    Cegłowski, Michał; Kurczewska, Joanna; Smoluch, Marek; Reszke, Edward; Silberring, Jerzy; Schroeder, Grzegorz

    2015-09-01

    In this paper, a procedure for the preconcentration and transport of mixtures of acids, bases, and drug components to a mass spectrometer using magnetic scavengers is presented. Flowing atmospheric pressure afterglow mass spectrometry (FAPA-MS) was used as an analytical method for identification of the compounds by thermal desorption from the scavengers. The proposed procedure is fast and cheap, and does not involve time-consuming purification steps. The developed methodology can be applied for trapping harmful substances in minute quantities, to transport them to specialized, remotely located laboratories.

  10. Prompt and Afterglow Emission Properties of Gamma-Ray Bursts with Spectroscopically Identified Supernovae

    NASA Technical Reports Server (NTRS)

    Kaneko, Yuki; Ramirez-Ruiz, Enrico; Patel, Sandeep K.; Kouveliotou, Chryssa; Granot, Jonathan; Rol, Evert; Woosley, Stan; in'tZand, Jean J. M.; vanderHorst, Alexander; Wijers, Ralph A. M. J.; Strom, Richard

    2006-01-01

    We present a detailed spectral analysis of the prompt and afterglow emission of four nearby GRBs (GRBs 980425, 030329, 031203, and 060218) that were spectroscopically found to be associated with type Ib/c supernovae. For each event, we investigated its spectral and luminosity evolution and estimated the total energy budget based on the broadband observations. We discuss the properties of the four events in comparison to general burst population, and infer the physical parameters involved in creation of these nearby GRB-SN events

  11. A possible bright blue supernova in the afterglow of GRB020305

    SciTech Connect

    Gorosabel, J.; Fynbo, J.P.U.; Fruchter, A.; Levan, A.; Hjorth,J.; Nugent, P.; Castro-Tirado, A.J.; Castro Ceron, J.M.; Rhoads, J.; Bersier, D.; Burud, I.

    2005-07-01

    We report on ground-based and HST(+STIS) imaging of the afterglow and host galaxy of the Gamma-Ray Burst (GRB) of March 5, 2002. The GRB occurred in a R=25.17+-0.14 galaxy, which apparently is part of an interacting system. The light curve of the optical afterglow shows are brightening, or at least a plateau, 12-16 days after the gamma-ray event. UBVRIK' multi-band imaging of the afterglow {approx}12 days after the GRB reveals a blue spectral energy distribution (SED). The SED is consistent with a power-law with a spectral index of beta=-0.63+-0.16,but there is tentative evidence for deviations away from a power-law. Unfortunately, a spectroscopic redshift has not been secured for GRB020305. From the SED we impose a redshift upper limit of z<{approx}2.8,hence excluding the pseudo redshift of 4.6 reported for this burst. We discuss the possibilities for explaining the light curve, SED and host galaxy properties for GRB 020305. The most natural interpretation of the light curve and the SED is an associated supernova (SN). Our data can not precisely determine the redshift of the GRB. The most favored explanation is a low redshift (z{approx}0.2) SN, but a higher redshift(z>{approx}0.5) SN can not be excluded. We also discuss less likely scenarios not based on SNe, like a burst occurring in a z=2.5 galaxy with an extinction curve similar to that of the Milky Way.

  12. Atmospheric pressure helium afterglow discharge detector for gas chromatography

    DOEpatents

    Rice, Gary; D'Silva, Arthur P.; Fassel, Velmer A.

    1986-05-06

    An apparatus for providing a simple, low-frequency electrodeless discharge system for atmospheric pressure afterglow generation. A single quartz tube through which a gas mixture is passed is extended beyond a concentric electrode positioned thereabout. A grounding rod is placed directly above the tube outlet to permit optical viewing of the discharge between the electrodes.

  13. Atmospheric pressure helium afterglow discharge detector for gas chromatography

    DOEpatents

    Rice, G.; D'Silva, A.P.; Fassel, V.A.

    1985-04-05

    An apparatus for providing a simple, low-frequency, electrodeless discharge system for atmospheric pressure afterglow generation. A single quartz tube through which a gas mixture is passed is extended beyond a concentric electrode positioned thereabout. A grounding rod is placed directly above the tube outlet to permit optical viewing of the discharge between the electrodes.

  14. The Optical Afterglow of a Short Gamma-ray Burst

    NASA Technical Reports Server (NTRS)

    Hjorth, Jens; Watson, Darach; Flynbo, Johan P.U.; Price, Paul A.; Jensen, Brian L.; Jorgensen, Uffe G.; Kubas, Daniel; Gorosabel, Javier; Jakobssonk, Pall; Sollerman, Jesper

    2005-01-01

    It has long been known that there are two classes of gamma-ray bursts (GRBs), principally distinguished by their durations. The breakthrough in our understanding of long-duration GRBs (greater than 2 seconds in duration), that ultimately linked them with energetic Type Ic supernovae, came about from the discovery of their long-lived X-ray and optical "afterglow", when precise and rapid localizations of the sources could finally be obtained. Recently, X-ray localizations have become available for short (less than 2 seconds in duration) GRBs, a hitherto elusive GRB population, that has evaded optical detection for more than thirty years. Here we report the discovery of transient optical emission (R approximately 23 mag) associated with a short GRB. This first short GRB afterglow is localized with sub-arcsecond accuracy onto the outskirts of a blue dwarf galaxy. Unless the optical and X-ray afterglow arise from different mechanisms our observations 33 h after the GRB suggest that, analogously to long GRBs, we observe synchrotron emission from ultrarelativistic ejecta (ZZZ CAN WE LIMIT GAMMA?). In contrast, we did not detect a bright supernova, as found in most nearby long GRB afterglows, which suggests a different origidstrongly constrain the nature of the short GRB progenitors.

  15. Recombination of H3+ Ions with Electrons in Afterglow Plasmas

    NASA Astrophysics Data System (ADS)

    Johnsen, Rainer; Glosik, Juraj; Dohnal, Petr; Rubovic, Peter; Kalosi, Abel; Plasil, Radek

    2015-09-01

    Our past and ongoing flowing and stationary afterglow experiments at temperatures from 60-340 K have resulted in a more complete picture of the plasma recombination of H3+ ions: (1) Optical absorption studies indicate that at T = 300 K both para and ortho H3+ ions recombine with nearly the same binary coefficient αbin ~ 0.6 × 10-7 cm3/s. However, at T = 60 K para H3+ recombines faster by about a factor of ~10 than does ortho H3+.(2) Earlier discrepancies between data obtained in plasmas and those obtained in merged-beam or storage-rings have been traced to ternary recombination due to ambient helium atoms and/or hydrogen molecules. Ternary recombination of H3+ due to He or H2 is more efficient by factors ~ 102 or 105, respectively, than expected from the theoretical model of Bates and Khare for atomic ions. (3) The ternary processes enhance recombination at low third-body densities (1017 cm-3) but then level off (``saturate'') when their contribution approaches ~ 1.5 × 10-7 cm3/s. This saturation can lead to the false inference that the overall recombination is binary, resulting in a recombination coefficient that is about 3 times too large. (4) A tentative complex model has been developed that rationalizes the observed effects. This work was partly supported by Czech Science Foundation projects GACR 14-14649P and GACR 15-15077S and by Charles University in Prague projects GAUK 692214, GAUK 572214, UNCE 204020/2012 and SVV 260.

  16. DISCOVERY AND REDSHIFT OF AN OPTICAL AFTERGLOW IN 71 deg{sup 2}: iPTF13bxl AND GRB 130702A

    SciTech Connect

    Singer, Leo P.; Brown, Duncan A.; Bradley Cenko, S.; Gehrels, Neil; McEnery, Julie; Kasliwal, Mansi M.; Mulchaey, John; Perley, Daniel A.; Kulkarni, S. R.; Bellm, Eric; Barlow, Tom; Cao, Yi; Horesh, Assaf; Ofek, Eran O.; Arcavi, Iair; Nugent, Peter E.; Bloom, Joshua S.; Corsi, Alessandra; Frail, Dale A.; Masci, Frank J.; and others

    2013-10-20

    We report the discovery of the optical afterglow of the γ-ray burst (GRB) 130702A, identified upon searching 71 deg{sup 2} surrounding the Fermi Gamma-ray Burst Monitor (GBM) localization. Discovered and characterized by the intermediate Palomar Transient Factory, iPTF13bxl is the first afterglow discovered solely based on a GBM localization. Real-time image subtraction, machine learning, human vetting, and rapid response multi-wavelength follow-up enabled us to quickly narrow a list of 27,004 optical transient candidates to a single afterglow-like source. Detection of a new, fading X-ray source by Swift and a radio counterpart by CARMA and the Very Large Array confirmed the association between iPTF13bxl and GRB 130702A. Spectroscopy with the Magellan and Palomar 200 inch telescopes showed the afterglow to be at a redshift of z = 0.145, placing GRB 130702A among the lowest redshift GRBs detected to date. The prompt γ-ray energy release and afterglow luminosity are intermediate between typical cosmological GRBs and nearby sub-luminous events such as GRB 980425 and GRB 060218. The bright afterglow and emerging supernova offer an opportunity for extensive panchromatic follow-up. Our discovery of iPTF13bxl demonstrates the first observational proof-of-principle for ∼10 Fermi-iPTF localizations annually. Furthermore, it represents an important step toward overcoming the challenges inherent in uncovering faint optical counterparts to comparably localized gravitational wave events in the Advanced LIGO and Virgo era.

  17. PROBING EXTRAGALACTIC DUST THROUGH NEARBY GAMMA-RAY BURST AFTERGLOWS

    SciTech Connect

    Liang, S. L.; Li Aigen E-mail: lia@missouri.ed

    2010-02-10

    The quantities and wavelength dependencies of the dust extinction along the lines of sight toward 33 nearby gamma-ray bursts (GRBs) with redshifts z < 2 are derived from fitting their afterglow spectral energy distributions. Unlike previous studies which often assume a specific extinction law like that of the Milky Way (MW) and the Large and Small Magellanic Clouds (LMC/SMC), our approach-we call it the 'Drude' approach-is more flexible in determining the true wavelength dependence of the extinction (while the shape of the extinction curve inferred from that relying on a priori assumption of a template extinction law is, of course, fixed). The extinction curves deduced from the Drude approach display a wide diversity of shapes, ranging from relatively flat curves to curves which are featureless and steeply rise toward the far-ultraviolet, and from curves just like that of the MW, LMC, and SMC to curves resembling that of the MW and LMC but lacking the 2175 A bump. The visual extinction A{sub V} derived from the Drude approach is generally larger by a factor of {approx}2-5 than that inferred by assuming a SMC-type template extinction law. Consistent with previous studies, the extinction-to-gas ratio is mostly smaller than that of the MW, and does not seem to correlate with the shape of the extinction curve. It is shown that the standard silicate-graphite interstellar grain model closely reproduces the extinction curves of all 33 GRBs host galaxies. For these 33 bursts at z < 2, we find no evidence for the evolution of the dust extinction, dust sizes, and relative abundances of silicate to graphite on redshifts.

  18. An inverse Compton origin for the 55 GeV photon in the late afterglow of GRB 130907A

    SciTech Connect

    Tang, Qing-Wen; Wang, Xiang-Yu; Tam, Pak-Hin Thomas E-mail: phtam@phys.nthu.edu.tw

    2014-06-20

    The extended high-energy gamma-ray (>100 MeV) emission which occurs well after the prompt gamma-ray bursts (GRBs) is usually explained as the afterglow synchrotron radiation. Here we report the analysis of Fermi Large Area Telescope observations of GRB 130907A. A 55 GeV photon compatible with the position of the burst was found about 5 hr after the prompt phase. The probability that this photon is associated with GRB 130907A is higher than 99.96%. The energy of this photon exceeds the maximum synchrotron photon energy at this time and its occurrence thus challenges the synchrotron mechanism as the origin for the extended high-energy >10 GeV emission. Modeling of the broadband spectral energy distribution suggests that such high energy photons can be produced by the synchrotron self-Compton emission of the afterglow.

  19. ON THE EMERGENT SPECTRA OF HOT PROTOPLANET COLLISION AFTERGLOWS

    SciTech Connect

    Miller-Ricci, Eliza; Meyer, Michael R.; Seager, Sara; Elkins-Tanton, Linda

    2009-10-10

    We explore the appearance of terrestrial planets in formation by studying the emergent spectra of hot molten protoplanets during their collisional formation. While such collisions are rare, the surfaces of these bodies may remain hot at temperatures of 1000-3000 K for up to millions of years during the epoch of their formation (of duration 10-100 Myr). These objects are luminous enough in the thermal infrared to be observable with current and next-generation optical/IR telescopes, provided that the atmosphere of the forming planet permits astronomers to observe brightness temperatures approaching that of the molten surface. Detectability of a collisional afterglow depends on properties of the planet's atmosphere-primarily on the mass of the atmosphere. A planet with a thin atmosphere is more readily detected, because there is little atmosphere to obscure the hot surface. Paradoxically, a more massive atmosphere prevents one from easily seeing the hot surface, but also keeps the planet hot for a longer time. In terms of planetary mass, more massive planets are also easier to detect than smaller ones because of their larger emitting surface areas-up to a factor of 10 in brightness between 1 and 10 M {sub +} planets. We present preliminary calculations assuming a range of protoplanet masses (1-10 M {sub +}), surface pressures (1-1000 bar), and atmospheric compositions, for molten planets with surface temperatures ranging from 1000 to 1800 K, in order to explore the diversity of emergent spectra that are detectable. While current 8 to 10 m class ground-based telescopes may detect hot protoplanets at wide orbital separations beyond 30 AU (if they exist), we will likely have to wait for next-generation extremely large telescopes or improved diffraction suppression techniques to find terrestrial planets in formation within several AU of their host stars.

  20. Nitric oxide kinetics in the afterglow of a diffuse plasma filament

    NASA Astrophysics Data System (ADS)

    Burnette, D.; Montello, A.; Adamovich, I. V.; Lempert, W. R.

    2014-08-01

    A suite of laser diagnostics is used to study kinetics of vibrational energy transfer and plasma chemical reactions in a nanosecond pulse, diffuse filament electric discharge and afterglow in N2 and dry air at 100 Torr. Laser-induced fluorescence of NO and two-photon absorption laser-induced fluorescence of O and N atoms are used to measure absolute, time-resolved number densities of these species after the discharge pulse, and picosecond coherent anti-Stokes Raman spectroscopy is used to measure time-resolved rotational temperature and ground electronic state N2(v = 0-4) vibrational level populations. The plasma filament diameter, determined from plasma emission and NO planar laser-induced fluorescence images, remains nearly constant after the discharge pulse, over a few hundred microseconds, and does not exhibit expansion on microsecond time scale. Peak temperature in the discharge and the afterglow is low, T ≈ 370 K, in spite of significant vibrational nonequilibrium, with peak N2 vibrational temperature of Tv ≈ 2000 K. Significant vibrational temperature rise in the afterglow is likely caused by the downward N2-N2 vibration-vibration (V-V) energy transfer. Simple kinetic modeling of time-resolved N, O, and NO number densities in the afterglow, on the time scale longer compared to relaxation and quenching time of excited species generated in the plasma, is in good agreement with the data. In nitrogen, the N atom density after the discharge pulse is controlled by three-body recombination and radial diffusion. In air, N, NO and O concentrations are dominated by the reverse Zel'dovich reaction, N + NO → N2 + O, and ozone formation reaction, O + O2 + M → O3 + M, respectively. The effect of vibrationally excited nitrogen molecules and excited N atoms on NO formation kinetics is estimated to be negligible. The results suggest that NO formation in the nanosecond pulse discharge is dominated by reactions of excited electronic states of nitrogen, occurring on

  1. THERMAL EMISSIONS SPANNING THE PROMPT AND THE AFTERGLOW PHASES OF THE ULTRA-LONG GRB 130925A

    SciTech Connect

    Basak, Rupal; Rao, A. R. E-mail: arrao@tifr.res.in

    2015-07-01

    GRB 130925A is an ultra-long gamma-ray burst (GRB), and it shows clear evidence for thermal emission in the soft X-ray data of the Swift/X-ray Telescope (XRT; ∼0.5 keV), lasting until the X-ray afterglow phase. Due to the long duration of the GRB, the burst could be studied in hard X-rays with high-resolution focusing detectors (NuSTAR). The blackbody temperature, as measured by the Swift/XRT, shows a decreasing trend until the late phase (Piro et al.) whereas the high-energy data reveal a significant blackbody component during the late epochs at an order of magnitude higher temperature (∼5 keV) compared to contemporaneous low energy data (Bellm et al.). We resolve this apparent contradiction by demonstrating that a model with two black bodies and a power law (2BBPL) is consistent with the data right from the late prompt emission to the afterglow phase. Both blackbodies show a similar cooling behavior up to late times. We invoke a structured jet, having a fast spine and a slower sheath layer, to identify the location of these blackbodies. Independent of the physical interpretation, we propose that the 2BBPL model is a generic feature of the prompt emission of all long GRBs, and the thermal emission found in the afterglow phase of different GRBs reflects the lingering thermal component of the prompt emission with different timescales. We strengthen this proposal by pointing out a close similarity between the spectral evolutions of this GRB and GRB 090618, a source with significant wide band data during the early afterglow phase.

  2. Afterglows, Redshifts, and Properties of Swift Gamma-Ray Bursts

    NASA Astrophysics Data System (ADS)

    Berger, E.; Kulkarni, S. R.; Fox, D. B.; Soderberg, A. M.; Harrison, F. A.; Nakar, E.; Kelson, D. D.; Gladders, M. D.; Mulchaey, J. S.; Oemler, A.; Dressler, A.; Cenko, S. B.; Price, P. A.; Schmidt, B. P.; Frail, D. A.; Morrell, N.; Gonzalez, S.; Krzeminski, W.; Sari, R.; Gal-Yam, A.; Moon, D.-S.; Penprase, B. E.; Jayawardhana, R.; Scholz, A.; Rich, J.; Peterson, B. A.; Anderson, G.; McNaught, R.; Minezaki, T.; Yoshii, Y.; Cowie, L. L.; Pimbblet, K.

    2005-11-01

    We present optical, near-IR, and radio follow-up of 16 Swift bursts, including our discovery of nine afterglows and a redshift determination for three. These observations, supplemented by data from the literature, provide an afterglow recovery rate of 52% in the optical/near-IR, much higher than in previous missions (BeppoSAX, HETE-2, INTEGRAL, and IPN). The optical/near-IR afterglows of Swift events are on average 1.8 mag fainter at t=12 hr than those of previous missions. The X-ray afterglows are similarly fainter than those of pre-Swift bursts. In the radio the limiting factor is the VLA threshold, and the detection rate for Swift bursts is similar to that for past missions. The redshift distribution of pre-Swift bursts peaked at z~1, whereas the six Swift bursts with measured redshifts are distributed evenly between 0.7 and 3.2. From these results we conclude that (1) the pre-Swift distributions were biased in favor of bright events and low-redshift events, (2) the higher sensitivity and accurate positions of Swift result in a better representation of the true burst redshift and brightness distributions (which are higher and dimmer, respectively), and (3) ~10% of the bursts are optically dark, as a result of a high redshift and/or dust extinction. We remark that the apparent lack of low-redshift, low-luminosity Swift bursts and the lower event rate than prelaunch estimates (90 vs. 150 per year) are the result of a threshold that is similar to that of BATSE. In view of these inferences, afterglow observers may find it advisable to make significant changes in follow-up strategies of Swift events. The faintness of the afterglows means that large telescopes should be employed as soon as the burst is localized. Sensitive observations in RIz and near-IR bands will be needed to discriminate between a typical z~2 burst with modest extinction and a high-redshift event. Radio observations will be profitable for a small fraction (~10%) of events. Finally, we suggest that

  3. Soft X-ray absorption excess in gamma-ray burst afterglow spectra: Absorption by turbulent ISM

    NASA Astrophysics Data System (ADS)

    Tanga, M.; Schady, P.; Gatto, A.; Greiner, J.; Krause, M. G. H.; Diehl, R.; Savaglio, S.; Walch, S.

    2016-10-01

    Two-thirds of long duration gamma-ray bursts (GRBs) show soft X-ray absorption in excess of the Milky Way. The column densities of metals inferred from UV and optical spectra differ from those derived from soft X-ray spectra, at times by an order of magnitude, with the latter being higher. The origin of the soft X-ray absorption excess observed in GRB X-ray afterglow spectra remains a heavily debated issue, which has resulted in numerous investigations on the effect of hot material both internal and external to the GRB host galaxy on our X-ray afterglow observations. Nevertheless, all models proposed so far have either only been able to account for a subset of our observations (i.e. at z> 2), or they have required fairly extreme conditions to be present within the absorbing material. In this paper, we investigate the absorption of the GRB afterglow by a collisionally ionised and turbulent interstellar medium (ISM). We find that a dense (3 cm-3) collisionally ionised ISM could produce UV/optical and soft X-ray absorbing column densities that differ by a factor of 10. However the UV/optical and soft X-ray absorbing column densities for such sightlines are 2-3 orders of magnitude lower in comparison to the GRB afterglow spectra. For those GRBs with a larger soft X-ray excess by up to an order of magnitude, the contribution in absorption from a turbulent ISM as considered here would ease the required conditions of additional absorbing components, such as the GRB circumburst medium and intergalactic medium.

  4. Gamma-Ray bursts: accumulating afterglow implications, progenitor clues, and prospects.

    PubMed

    Mészáros, P

    2001-01-01

    Gamma-ray bursts (GRBs) are sudden, intense flashes of gamma rays that, for a few blinding seconds, light up in an otherwise fairly dark gamma-ray sky. They are detected at the rate of about once a day, and while they are on, they outshine every other gamma-ray source in the sky, including the sun. Major advances have been made in the last 3 or 4 years, including the discovery of slowly fading x-ray, optical, and radio afterglows of GRBs, the identification of host galaxies at cosmological distances, and evidence showing that many GRBs are associated with star-forming regions and possibly supernovae. Progress has been made in understanding how the GRB and afterglow radiation arises in terms of a relativistic fireball shock model. These advances have opened new vistas and questions on the nature of the central engine, the identity of their progenitors, the effects of the environment, and their possible gravitational wave, cosmic ray, and neutrino luminosity. The debates on these issues indicate that GRBs remain among the most mysterious puzzles in astrophysics. PMID:11141551

  5. Gamma-Ray bursts: accumulating afterglow implications, progenitor clues, and prospects.

    PubMed

    Mészáros, P

    2001-01-01

    Gamma-ray bursts (GRBs) are sudden, intense flashes of gamma rays that, for a few blinding seconds, light up in an otherwise fairly dark gamma-ray sky. They are detected at the rate of about once a day, and while they are on, they outshine every other gamma-ray source in the sky, including the sun. Major advances have been made in the last 3 or 4 years, including the discovery of slowly fading x-ray, optical, and radio afterglows of GRBs, the identification of host galaxies at cosmological distances, and evidence showing that many GRBs are associated with star-forming regions and possibly supernovae. Progress has been made in understanding how the GRB and afterglow radiation arises in terms of a relativistic fireball shock model. These advances have opened new vistas and questions on the nature of the central engine, the identity of their progenitors, the effects of the environment, and their possible gravitational wave, cosmic ray, and neutrino luminosity. The debates on these issues indicate that GRBs remain among the most mysterious puzzles in astrophysics.

  6. Measuring of the nonlocal EDF of penning electrons by the wall electrode in the plasma afterglow

    NASA Astrophysics Data System (ADS)

    Kudryavtsev, Anatoly; Kapustin, Kirill; Sayfutdinov, Almaz

    2014-10-01

    In was patented ionization detector for gas analysis, based on the method of collisional electron spectroscopy (CES), which allows working at a high gas pressure. The CES method provides an opportunity to analyze energy of nonlocal electrons released during Penning ionization of atomic or molecular impurities by metastable helium atoms. In this case, the EDF of fast electrons will be narrow peaks that correspond to the energies of their appearance in Penning ionization. To realize the CES method at high (atmospheric) pressure the plasma gap must be small L < 0.1 mm. In this condition the traditional Langmuir probe is impossible to use for measuring the EDF. To overcome this difficulty in was proposed to use afterglow plasma and one of the electrodes as a measuring probe for the registration of EDF of fast penning electrons. In this paper we simulate the afterglow of argon discharge between parallel electrodes and show that EDF and electron sources of Penning ionization are determined by the first derivative of the current to the wall electrode with respect to potential. This work was supported by RSCF and SPbSU.

  7. Gamma-ray bursts: afterglows from cylindrical jets

    NASA Astrophysics Data System (ADS)

    Cheng, K. S.; Huang, Y. F.; Lu, T.

    2001-08-01

    Nearly all previous discussions on beaming effects in gamma-ray bursts (GRBs) have assumed a conical geometry. However, more and more observations on relativistic jets in radio galaxies, active galactic nuclei, and `microquasars' in the Galaxy have shown that many of these outflows are not conical, but cylindrical, i.e. they maintain constant cross-sections at large scales. Thus it is necessary to discuss the possibility of gamma-ray bursts being due to highly collimated cylindrical jets, not conical ones. Here we study the dynamical evolution of cylindrical jets and discuss their afterglows. Both analytical and numerical results are presented. It is shown that when the lateral expansion is not taken into account, a cylindrical jet typically remains highly relativistic for ~108-109s. During this relativistic phase, the optical afterglow at first decays as Sν~t-p/2, where p is the index characterizing the power-law energy distribution of electrons. Then the light curve steepens to Sν~t-(p+1)/2 due to cooling of electrons. After entering the non-relativistic phase (i.e. t>=1011s), the afterglow is Sν~t-(5p-4)/6. However, if the cylindrical jet expands laterally at the comoving sound speed, then the decay becomes Sν~t-p and Sν~t-(15p-21)/10-t-(15p-20)/10 in the ultrarelativistic and in the non-relativistic phase respectively. Note that in both cases the light curve turns flatter after the relativistic-Newtonian transition point, which differs markedly from the behaviour of a conical jet. It is suggested that some GRBs with afterglows decaying as t-1.1-t-1.3 may be due to cylindrical jets, not necessarily isotropic fireballs.

  8. Spectroscopic Observations of the Bright Afterglow of GRB021004

    NASA Astrophysics Data System (ADS)

    Harrison, Fiona

    2001-09-01

    One of the holy grails of gamma-ray burst research is to detect X-ray line signatures from an afterglow with high statistical significance. Of all possible observations, this perhaps offers the best chance of constraining the GRB mechanism and environment, and could provide the "smoking gun" signature connecting GRBs to massive stellar deaths. In order to accomplish this, we know long observations within one day of the event are necessary.

  9. Self organized criticality in an one dimensional magnetized grid. Application to GRB X-ray afterglows

    NASA Astrophysics Data System (ADS)

    Harko, Tiberiu; Mocanu, Gabriela; Stroia, Nicoleta

    2015-05-01

    A simplified one dimensional grid is used to model the evolution of magnetized plasma flow. We implement diffusion laws similar to those so-far used to model magnetic reconnection with Cellular Automata. As a novelty, we also explicitly superimpose a background flow. The aim is to numerically investigate the possibility that Self-Organized Criticality appears in a one dimensional magnetized flow. The cellular automaton's cells store information about the parameter relevant to the evolution of the system being modelled. Under the assumption that this parameter stands for the magnetic field, the magnetic energy released by one grid cell during one individual relaxation event is also computed. Our results show that indeed in this system Self-Organized Criticality is established. The possible applications of this model to the study of the X-ray afterglows of GRBs is also briefly considered.

  10. TWO POPULATIONS OF GAMMA-RAY BURST RADIO AFTERGLOWS

    SciTech Connect

    Hancock, P. J.; Gaensler, B. M.; Murphy, T.

    2013-10-20

    The detection rate of gamma-ray burst (GRB) afterglows is ∼30% at radio wavelengths, much lower than in the X-ray (∼95%) or optical (∼70%) bands. The cause of this low radio detection rate has previously been attributed to limited observing sensitivity. We use visibility stacking to test this idea, and conclude that the low detection rate is instead due to two intrinsically different populations of GRBs: radio-bright and radio-faint. We calculate that no more than 70% of GRB afterglows are truly radio-bright, leaving a significant population of GRBs that lack a radio afterglow. These radio-bright GRBs have higher gamma-ray fluence, isotropic energies, X-ray fluxes, and optical fluxes than the radio-faint GRBs, thus confirming the existence of two physically distinct populations. We suggest that the gamma-ray efficiency of the prompt emission is responsible for the difference between the two populations. We also discuss the implications for future radio and optical surveys.

  11. Tuning the afterglow plasma composition in Ar/N2/O2 mixtures: characteristics of a flowing surface-wave microwave discharge system

    NASA Astrophysics Data System (ADS)

    Kutasi, Kinga; Noël, Cédric; Belmonte, Thierry; Guerra, Vasco

    2016-10-01

    A self-consistent kinetic model is used to study the possibility of tuning the plasma composition in the afterglow of a flowing surface-wave microwave discharge by the different discharge and system parameters in the case of 90%Ar-10%(N2-O2) and N2-O2 mixtures. The afterglow system consists of a 0.5 cm diameter quartz tube of 50 cm in length—where the discharge is generated and the early-afterglow develops—and an afterglow reactor. The plasma composition is studied at the end of the discharge plasma column and at the reactor inlet as a function of the N2:O2 ratio for selected conditions, which are set with the system parameters and are illustrated in the experimental set-up. The validity of the model used is proven by the agreement of the calculated atomic densities with those measured by mass spectrometry. Due to the pressure drop along the tube, the position of the discharge (which also defines the lengths of the early-afterglow, t aft) and the discharge pressure (p dis) can be set with the position of the wave coupler—surfatron—along the tube at a constant gas flow rate (which defines the pressure in the reactor, p reac). It is shown that the relative densities of species at the end of plasma column, which constitute the initial condition for the afterglow, depend on the discharge pressure. Therefore, at a constant gas flow rate with the position of the surfatron the plasma composition in the reactor is changing due to the variation of both the p dis and t aft. The evolution of the plasma composition is also studied when both the surfatron’s position and the gas flow rate are changed, realizing conditions (i) with the same p dis, and different t aft and p reac, and (ii) with the same t aft, and different p dis and p reac. Comparing the N2-O2 binary and the ternary mixtures, it is shown that the atomic densities obtained in the binary mixtures can be reproduced in ternary mixtures with different N2:O2 ratios. Furthermore, according to the spectra

  12. Model based manipulator control

    NASA Technical Reports Server (NTRS)

    Petrosky, Lyman J.; Oppenheim, Irving J.

    1989-01-01

    The feasibility of using model based control (MBC) for robotic manipulators was investigated. A double inverted pendulum system was constructed as the experimental system for a general study of dynamically stable manipulation. The original interest in dynamically stable systems was driven by the objective of high vertical reach (balancing), and the planning of inertially favorable trajectories for force and payload demands. The model-based control approach is described and the results of experimental tests are summarized. Results directly demonstrate that MBC can provide stable control at all speeds of operation and support operations requiring dynamic stability such as balancing. The application of MBC to systems with flexible links is also discussed.

  13. 'Self-absorbed' GeV light curves of gamma-ray burst afterglows

    SciTech Connect

    Panaitescu, A.; Vestrand, W. T.; Woźniak, P.

    2014-06-10

    We investigate the effect that the absorption of high-energy (above 100 MeV) photons produced in gamma-ray burst afterglow shocks has on the light curves and spectra of Fermi Large Area Telescope (LAT) afterglows. Afterglows produced by the interaction of a relativistic outflow with a wind-like medium peak when the blast wave deceleration sets in, and the afterglow spectrum could be hardening before that peak, as the optical thickness to pair formation is decreasing. In contrast, in afterglows produced in the interaction with a homogeneous medium, the optical thickness to pair formation should increase and yield a light curve peak when it reaches unity, followed by a fast light curve decay, accompanied by spectral softening. If energy is injected in the blast wave, then the accelerated increase of the optical thickness yields a convex afterglow light curve. Other features, such as a double-peak light curve or a broad hump, can arise from the evolution of the optical thickness to photon-photon absorption. Fast decays and convex light curves are seen in a few LAT afterglows, but the expected spectral softening is rarely seen in (and difficult to measure with) LAT observations. Furthermore, for the effects of photon-photon attenuation to shape the high-energy afterglow light curve without attenuating it too much, the ejecta initial Lorentz factor must be in a relatively narrow range (50-200), which reduces the chance of observing those effects.

  14. GRB off-axis afterglows and the emission from the accompanying supernovae

    NASA Astrophysics Data System (ADS)

    Kathirgamaraju, Adithan; Barniol Duran, Rodolfo; Giannios, Dimitrios

    2016-09-01

    Gamma-ray burst (GRB) afterglows are likely produced in the shock that is driven as the GRB jet interacts with the external medium. Long-duration GRBs are also associated with powerful supernovae (SNe). We consider the optical and radio afterglows of long GRBs for both blasts viewed along the jet axis (`on-axis' afterglows) and misaligned observes (`off-axis' afterglows). Comparing the optical emission from the afterglow with that of the accompanying SN, using SN 1998bw as an archetype, we find that only a few per cent of afterglows viewed off-axis are brighter than the SN. For observable optical off-axis afterglows, the viewing angle is at most twice the half-opening angle of the GRB jet. Radio off-axis afterglows should be detected with upcoming radio surveys within a few hundred Mpc. We propose that these surveys will act as `radio triggers', and that dedicated radio facilities should follow-up these sources. Follow-ups can unveil the presence of the radio SN remnant, if present. In addition, they can probe the presence of a mildly relativistic component, either associated with the GRB jet or the SN ejecta, expected in these sources.

  15. Summary of the workshop on gamma-ray burst afterglows at the 34th COSPAR meeting

    NASA Astrophysics Data System (ADS)

    Craig Wheeler, J.

    2004-01-01

    A summary is given of the presentations at the COSPAR workshop on γ-ray bursts with some personal commentary on the contributions, the SN/GRB connection, and on the role of magnetic fields in γ-ray bursts and their afterglows. Of special interest were the accumulated arguments for strong collimation and associated reduction in the total required energy for γ-ray bursts. Significant discussion was also devoted to the issues associated with iron and metal lines in X-ray spectra. It is important to note that some of the afterglows seem to require ambient densities ≪1 g cm -3, rather incompatible with a massive star environment. Of associated difficulty is the fact that few, if any, afterglows seem consistent with the r-2 wind expected for a massive star model. There are reasons to think that if γ-ray bursts are associated with supernovae they are of Type Ic. This suggests that any wind present might be rich in carbon and oxygen, not hydrogen or helium. If γ-ray bursts are narrowly collimated, then the burst is only probing a small portion of any wind, perhaps just that time-dependent and isotropic structure directly along the rotation axis. The characteristics of "hypernovae" may be the result of orientation effects in a mildly inhomogeneous set of progenitors, rather than requiring an excessive total energy or luminosity. The recent event GRB 021004 provided a rich photometric and spectroscopic record and perhaps the most direct evidence yet for the association of a specific γ-ray burst with a massive star progenitor. If the magnetic field plays a significant role in launching a relativistic γ-ray burst jet from within a collapsing star, then the magnetic field may also play a role in the propagation, collimation, and stability of that jet within and beyond the star. The magneto-rotational instability (MRI) can operate under conditions of moderate rotation. This means that the MRI will be at work generating strong fields exponentially rapidly even as the

  16. DISCOVERY OF SMOOTHLY EVOLVING BLACKBODIES IN THE EARLY AFTERGLOW OF GRB 090618: EVIDENCE FOR A SPINE–SHEATH JET?

    SciTech Connect

    Basak, Rupal; Rao, A. R. E-mail: arrao@tifr.res.in

    2015-10-20

    GRB 090618 is a bright gamma-ray burst (GRB) with multiple pulses. It shows evidence of thermal emission in the initial pulses as well as in the early afterglow phase. Because high-resolution spectral data from the Swift/X-ray Telescope (XRT) are available for the early afterglow, we investigate the shape and evolution of the thermal component in this phase using data from the Swift/Burst Alert Telescope (BAT), the Swift/XRT, and the Fermi/Gamma-ray Burst Monitor detectors. An independent fit to the BAT and XRT data reveals two correlated blackbodies with monotonically decreasing temperatures. Hence, we investigated the combined data with a model consisting of two blackbodies and a power law (2BBPL), a model suggested for several bright GRBs. We elicit the following interesting features of the 2BBPL model: (1) the same model is applicable from the peak of the last pulse in the prompt emission to the afterglow emission, (2) the ratio of temperatures and the fluxes of the two blackbodies remains constant throughout the observations, (3) the blackbody temperatures and fluxes show a monotonic decrease with time, with the BB fluxes dropping about a factor of two faster than that of the power-law (PL) emission, and (4) attributing the blackbody emission to photospheric emissions, we find that the photospheric radii increase very slowly with time, and the lower-temperature blackbody shows a larger emitting radius than that of the higher-temperature blackbody. We find some evidence that the underlying shape of the nonthermal emission is a cutoff power law rather than a PL. We sketch a spine–sheath jet model to explain our observations.

  17. PANCHROMATIC OBSERVATIONS OF THE TEXTBOOK GRB 110205A: CONSTRAINING PHYSICAL MECHANISMS OF PROMPT EMISSION AND AFTERGLOW

    SciTech Connect

    Zheng, W.; Shen, R. F.; Sakamoto, T.; Beardmore, A. P.; De Pasquale, M.; Wu, X. F.; Zhang, B.; Gorosabel, J.; Urata, Y.; Sugita, S.; Pozanenko, A.; Sahu, D. K.; Im, M.; Ukwatta, T. N.; Andreev, M.; Klunko, E. E-mail: rfshen@astro.utoronto.ca; and others

    2012-06-01

    We present a comprehensive analysis of a bright, long-duration (T{sub 90} {approx} 257 s) GRB 110205A at redshift z = 2.22. The optical prompt emission was detected by Swift/UVOT, ROTSE-IIIb, and BOOTES telescopes when the gamma-ray burst (GRB) was still radiating in the {gamma}-ray band, with optical light curve showing correlation with {gamma}-ray data. Nearly 200 s of observations were obtained simultaneously from optical, X-ray, to {gamma}-ray (1 eV to 5 MeV), which makes it one of the exceptional cases to study the broadband spectral energy distribution during the prompt emission phase. In particular, we clearly identify, for the first time, an interesting two-break energy spectrum, roughly consistent with the standard synchrotron emission model in the fast cooling regime. Shortly after prompt emission ({approx}1100 s), a bright (R = 14.0) optical emission hump with very steep rise ({alpha} {approx} 5.5) was observed, which we interpret as the reverse shock (RS) emission. It is the first time that the rising phase of an RS component has been closely observed. The full optical and X-ray afterglow light curves can be interpreted within the standard reverse shock (RS) + forward shock (FS) model. In general, the high-quality prompt and afterglow data allow us to apply the standard fireball model to extract valuable information, including the radiation mechanism (synchrotron), radius of prompt emission (R{sub GRB} {approx} 3 Multiplication-Sign 10{sup 13} cm), initial Lorentz factor of the outflow ({Gamma}{sub 0} {approx} 250), the composition of the ejecta (mildly magnetized), the collimation angle, and the total energy budget.

  18. The Discovery and Broadband Follow-Up of the Transient Afterglow of GRB 980703

    NASA Technical Reports Server (NTRS)

    Bloom, J. S.; Frail, D. A.; Kulkarni, S. R.; Djorgovski, S. G.; Halpern, J. P.; Marzke, R. O.; Patton, D. R.; Oke, J. B.; Horne, K. D.; Gomer, R.; Goodrich, R.; Campbell, R.; Moriarity-Schieven, G. H.; Redman, R. O.; Feldman, P. A.; Costa, E.; Masetti, N.

    1998-01-01

    We report on the discovery of the radio, infrared, and optical transient coincident with an X-ray transient proposed to be the afterglow of GRB 980703. At later times when the transient has faded below detection, we see an underlying galaxy with R = 22.6; this galaxy is the brightest host galaxy (by nearly 2 mag) of any cosmological gamma-ray burst (GRB) thus far. In keeping with an established trend, the GRB is not significantly offset from the host galaxy. Interpreting the multiwavelength data in the framework of the popular fireball model requires that the synchrotron cooling break was between the optical and X-ray bands on 1998 July 8.5 UT and that the intrinsic extinction of the transient is A(sub v) = 0.9. This is somewhat higher than the extinction for the galaxy as a whole, as estimated from spectroscopy.

  19. Electron-Ion Recombination Rate Coefficient Measurements in a Flowing Afterglow Plasma

    NASA Technical Reports Server (NTRS)

    Gougousi, Theodosia; Golde, Michael F.; Johnsen, Rainer

    1996-01-01

    The flowing-afterglow technique in conjunction with computer modeling of the flowing plasma has been used to determine accurate dissociative-recombination rate coefficients alpha for the ions O2(+), HCO(+), CH5(+), C2H5(+), H3O(+), CO2(+), HCO2(+), HN2O(+), and N2O(+) at 295 K. We find that the simple form of data analysis that was employed in earlier experiments was adequate and we largely confirm earlier results. In the case of HCO(+) ions, published coefficients range from 1.1 X 10(exp -7) to 2.8 x 10(exp -7) cu cm/S, while our measurements give a value of 1.9 x 10(exp -7) cu cm/S.

  20. Prompt and Afterglow Emmision Properties of Gamma-ray Bursts with Spectroscopically Identified Supernovae

    NASA Technical Reports Server (NTRS)

    Kaneko, Yuki; Ramirez-Ruiz, Enrico; Granot, Jonathan; Kouveliotou, Chryssa; Woosley, Stan E.; Patel, Sandeep K.; Rol, Evert; In'TZant, Jean J. M.; VanDerHorst, Alexander J.; Wijers, Ralph A. M. J.; Strom, Richard

    2007-01-01

    We present a detailed spectral analysis of the prompt and afterglow emission of four nearby long-soft gamma-ray bursts (GRBs 980425,030329,031203, and 060218) that were spectroscopically found to be associated with Type IC supernovae and compare them to the general GRB population. For each event, we investigate the spectral and luminosity evolution and estimate the total energy budget based on broadband observations. The observational inventory for these events has become rich enough to allow estimates of their energy content in relativistic and subrelativistic form. The result is a global portrait of the effects of the physical processes responsible for producing long-soft GRBs. In particular, we find that the values of the energy released in mildly relativistic out8ows appears to have a sigruficantly smaller scatter than those found in highly relativistic ejecta. This is consistent with a picture in which the energy released inside the progenitor star is roughly standard, while the fracti

  1. Wide field x-ray telescopes: Detecting x-ray transients/afterglows related to GRBs

    SciTech Connect

    Hudec, Rene; Pina, Ladislav; Inneman, Adolf; Gorenstein, Paul

    1998-05-16

    The recent discovery of X-ray afterglows of GRBs opens the possibility of analyses of GRBs by their X-ray detections. However, imaging X-ray telescopes in current use mostly have limited fields of view. Alternative X-ray optics geometries achieving very large fields of view have been theoretically suggested in the 70's but not constructed and used so far. We review the geometries and basic properties of the wide-field X-ray optical systems based on one- and two-dimensional lobster-eye geometry and suggest technologies for their development and construction. First results of the development of double replicated X-ray reflecting flats for use in one-dimensional X-ray optics of lobster-eye type are presented and discussed. The optimum strategy for locating GRBs upon their X-ray counterparts is also presented and discussed.

  2. Model-Based Systems

    NASA Technical Reports Server (NTRS)

    Frisch, Harold P.

    2007-01-01

    Engineers, who design systems using text specification documents, focus their work upon the completed system to meet Performance, time and budget goals. Consistency and integrity is difficult to maintain within text documents for a single complex system and more difficult to maintain as several systems are combined into higher-level systems, are maintained over decades, and evolve technically and in performance through updates. This system design approach frequently results in major changes during the system integration and test phase, and in time and budget overruns. Engineers who build system specification documents within a model-based systems environment go a step further and aggregate all of the data. They interrelate all of the data to insure consistency and integrity. After the model is constructed, the various system specification documents are prepared, all from the same database. The consistency and integrity of the model is assured, therefore the consistency and integrity of the various specification documents is insured. This article attempts to define model-based systems relative to such an environment. The intent is to expose the complexity of the enabling problem by outlining what is needed, why it is needed and how needs are being addressed by international standards writing teams.

  3. Fermi and Swift Gamma-Ray Burst Afterglow Population Studies

    NASA Technical Reports Server (NTRS)

    Racusin, J. L.; Oates, S. R.; Schady, P.; Burrows, D. N.; de Pasquale, M.; Donato, D.; Gehrels, N.; Koch, S.; McEnery, J.; Piran, T.; Roming, P.; Sakamoto, T.; Swenson, C.; Virgili, F.; Wanderman, D.; Zhang, B.

    2011-01-01

    The new and extreme population of GRBs detected by Fermi-LAT shows several new features in high energy gamma-rays that are providing interesting and unexpected clues into GRB prompt and afterglow emission mechanisms. Over the last 6 years, it has been Swift that has provided the robust data set of UV/optical and X-ray afterglow observations that opened many windows into components of GRB emission structure. The relationship between the LAT GRBs and the well studied, fainter, less energetic GRBs detected by Swift-BAT is only beginning to be explored by multiwavelength studies. We explore the large sample of GRBs detected by BAT only, BAT and Fermi-GBM, and GBM and LAT, focusing on these samples separately in order to search for statistically significant differences between the populations, using only those GRBs with measured redshifts in order to physically characterize these objects. We disentangle which differences are instrumental selection effects versus intrinsic properties, in order to better understand the nature of the special characteristics of the LAT bursts.

  4. Fermi and Swift Gamma-Ray Burst Afterglow Population Studies

    NASA Technical Reports Server (NTRS)

    Racusin, Judith I.

    2011-01-01

    The new and extreme population of GRBs detected by Fermi-LAT shows several new features in high energy gamma-rays that are providing interesting and unexpected clues into GRB prompt and afterglow emission mechanisms. Over the last 6 years, it has been Swift that has provided the robust data set of UV/optical and X-ray afterglow observations that opened many windows into components of GRB emission structure. The relationship between the LAT GRBs and the well studied, fainter, less energetic GRBs detected by Swift-BAT is only beginning to be explored by multi-wavelength studies. We explore the large sample of GRBs detected by BAT only, BAT and Fermi-GBM, and GBM and LAT, focusing on these samples separately in order to search for statistically significant differences between the populations, using only those GRBs with measured redshifts in order to physically characterize these objects. We disentangle which differences are instrumental selection effects versus intrinsic properties, in order to better understand the nature of the special characteristics of the LAT bursts.

  5. Fermi and Swift Gamma-Ray Burst Afterglow Population Studies

    NASA Technical Reports Server (NTRS)

    Racusin, Judith L.; Oates, S. R.; Schady, P.; Burrows, D. N.; dePasquale, M.; Donato, D.; Gehrels, N.; Koch, S.; McEnery, J.; Piran, T.; Roming, P.; Sakamoto, T.; Swenson, C.; Troja, E.; Vasileiou, V.; Virgili, F.; Wanderman, D.; Zhang, B.

    2011-01-01

    The new and extreme population of GRBs detected by Fermi -LAT shows several new features in high energy gamma-rays that are providing interesting and unexpected clues into GRB prompt and afterglow emission mechanisms. Over the last 6 years, it has been Swift that has provided the robust dataset of UV/optical and X-ray afterglow observations that opened many windows into components of GRB emission structure. The relationship between the LAT detected GRBs and the well studied, fainter, less energetic GRBs detected by Swift -BAT is only beginning to be explored by multi-wavelength studies. We explore the large sample of GRBs detected by BAT only, BAT and Fermi -GBM, and GBM and LAT, focusing on these samples separately in order to search for statistically significant differences between the populations, using only those GRBs with measured redshifts in order to physically characterize these objects. We disentangle which differences are instrumental selection effects versus intrinsic properties, in order to better understand the nature of the special characteristics of the LAT bursts.

  6. The hidden X-ray breaks in afterglow light curves

    SciTech Connect

    Curran, P. A.; Wijers, R. A. M. J.; Horst, A. J. van der; Starling, R. L. C.

    2008-05-22

    Gamma-Ray Burst (GRB) afterglow observations in the Swift era have a perceived lack of achromatic jet breaks compared to the BeppoSAX, or pre-Swift era. Specifically, relatively few breaks, consistent with jet breaks, are observed in the X-ray light curves of these bursts. If these breaks are truly missing, it has serious consequences for the interpretation of GRB jet collimation and energy requirements, and the use of GRBs as standard candles.Here we address the issue of X-ray breaks which are possibly 'hidden' and hence the light curves are misinterpreted as being single power-laws. We show how a number of precedents, including GRB 990510 and GRB 060206, exist for such hidden breaks and how, even with the well sampled light curves of the Swift era, these breaks may be left misidentified. We do so by synthesising X-ray light curves and finding general trends via Monte Carlo analysis. Furthermore, in light of these simulations, we discuss how to best identify achromatic breaks in afterglow light curves via multi-wavelength analysis.

  7. The radio afterglow of Swift J1644+57 reveals a powerful jet with fast core and slow sheath

    NASA Astrophysics Data System (ADS)

    Mimica, P.; Giannios, D.; Metzger, B. D.; Aloy, M. A.

    2015-07-01

    We model the non-thermal transient Swift J1644+57 as resulting from a relativistic jet powered by the accretion of a tidally disrupted star on to a supermassive black hole. Accompanying synchrotron radio emission is produced by the shock interaction between the jet and the dense circumnuclear medium, similar to a gamma-ray burst afterglow. An open mystery, however, is the origin of the late-time radio re-brightening, which occurred well after the peak of the jetted X-ray emission. Here, we systematically explore several proposed explanations for this behaviour by means of multidimensional hydrodynamic simulations coupled to a self-consistent radiative transfer calculation of the synchrotron emission. Our main conclusion is that the radio afterglow of Swift J1644+57 is not naturally explained by a jet with a one-dimensional top-hat angular structure. However, a more complex angular structure comprised of an ultrarelativistic core (Lorentz factor Γ ˜ 10) surrounded by a slower (Γ ˜ 2) sheath provides a reasonable fit to the data. Such a geometry could result from the radial structure of the super-Eddington accretion flow or as the result of jet precession. The total kinetic energy of the ejecta that we infer of ˜ few 1053 erg requires a highly efficient jet launching mechanism. Our jet model providing the best fit to the light curve of the on-axis event Swift J1644+57 is used to predict the radio light curves for off-axis viewing angles. Implications for the presence of relativistic jets from tidal disruption events (TDEs) detected via their thermal disc emission, as well as the prospects for detecting orphan TDE afterglows with upcoming wide-field radio surveys and resolving the jet structure with long baseline interferometry, are discussed.

  8. Model Based Definition

    NASA Technical Reports Server (NTRS)

    Rowe, Sidney E.

    2010-01-01

    In September 2007, the Engineering Directorate at the Marshall Space Flight Center (MSFC) created the Design System Focus Team (DSFT). MSFC was responsible for the in-house design and development of the Ares 1 Upper Stage and the Engineering Directorate was preparing to deploy a new electronic Configuration Management and Data Management System with the Design Data Management System (DDMS) based upon a Commercial Off The Shelf (COTS) Product Data Management (PDM) System. The DSFT was to establish standardized CAD practices and a new data life cycle for design data. Of special interest here, the design teams were to implement Model Based Definition (MBD) in support of the Upper Stage manufacturing contract. It is noted that this MBD does use partially dimensioned drawings for auxiliary information to the model. The design data lifecycle implemented several new release states to be used prior to formal release that allowed the models to move through a flow of progressive maturity. The DSFT identified some 17 Lessons Learned as outcomes of the standards development, pathfinder deployments and initial application to the Upper Stage design completion. Some of the high value examples are reviewed.

  9. The Swift Discovery of X-ray Afterglows Accompanying Short Bursts from SGR 1900+14

    NASA Technical Reports Server (NTRS)

    Nakagawa, Y. E.; Sakamoto, T.; Sato, G.; Gehrels, N.; Hurley, K.; Palmer, D. M.

    2008-01-01

    The discovery of X-ray afterglows accompanying two short bursts from SGR1900+14 is presented. The afterglow luminosities at the end of each observation are lower by 30-50% than their initial luminosities, and decay with power law indices p approx. 0.2-0.4. Their initial bolometric luminosities are L approx. 10(exp 34)- 10(exp 35) erg/s. We discuss analogies and differences between the X-ray afterglows of SGR short bursts and short gamma-ray bursts.

  10. Analytically useful spectra excited in an atmospheric pressure active nitrogen afterglow

    SciTech Connect

    Rice, G.W.; D'Silva, A.P.; Fassel, V.A.

    1984-03-01

    An atmospheric pressure active nitrogen (APAN) discharge has been utilized for producing characteristic molecular emissions from nonmetallic species introduced into the afterglow region of the discharge. The addition of inorganic S-, P-, B-, Cl-, and Br-containing compounds into the afterglow has resulted in the formation of excited S/sub 2/, PN, BO, NCl, and NBr species, respectively. Intense molecular Br/sub 2/ emission and I/sub 2/ emission, as well as atomic I emission, have also been observed. Preliminary analytical utilization of the molecular or atomic emissions observed revealed that the APAN afterglow may serve as a potentially useful detector for the aforementioned elements.

  11. DYNAMICS AND AFTERGLOW LIGHT CURVES OF GAMMA-RAY BURST BLAST WAVES WITH A LONG-LIVED REVERSE SHOCK

    SciTech Connect

    Uhm, Z. Lucas; Zhang Bing; Hascoeet, Romain; Daigne, Frederic; Mochkovitch, Robert; Park, Il H.

    2012-12-20

    We perform a detailed study on the dynamics of a relativistic blast wave with the presence of a long-lived reverse shock (RS). Although a short-lived RS has been widely considered, the RS is believed to be long-lived as a consequence of a stratification expected on the ejecta Lorentz factors. The existence of a long-lived RS causes the forward shock (FS) dynamics to deviate from a self-similar Blandford-McKee solution. Employing the ''mechanical model'' that correctly incorporates the energy conservation, we present an accurate solution for both the FS and RS dynamics. We conduct a sophisticated calculation of the afterglow emission. Adopting a Lagrangian description of the blast wave, we keep track of an adiabatic evolution of numerous shells between the FS and RS. An evolution of the electron spectrum is also followed individually for every shell. We then find the FS and RS light curves by integrating over the entire FS and RS shocked regions, respectively. Exploring a total of 20 different ejecta stratifications, we explain in detail how a stratified ejecta affects its blast wave dynamics and afterglow light curves. We show that, while the FS light curves are not sensitive to the ejecta stratifications, the RS light curves exhibit much richer features, including steep declines, plateaus, bumps, re-brightenings, and a variety of temporal decay indices. These distinctive RS features may be observable if the RS has higher values of the microphysics parameters than the FS. We discuss possible applications of our results in understanding the gamma-ray burst afterglow data.

  12. The distribution of equivalent widths in long GRB afterglow spectra

    NASA Astrophysics Data System (ADS)

    de Ugarte Postigo, A.; Fynbo, J. P. U.; Thöne, C. C.; Christensen, L.; Gorosabel, J.; Milvang-Jensen, B.; Schulze, S.; Jakobsson, P.; Wiersema, K.; Sánchez-Ramírez, R.; Leloudas, G.; Zafar, T.; Malesani, D.; Hjorth, J.

    2012-12-01

    Context. The extreme brightness of gamma-ray burst (GRB) afterglows and their simple spectral shape make them ideal beacons to study the interstellar medium of their host galaxies through absorption line spectroscopy at almost any redshift. Aims: We describe the distribution of rest-frame equivalent widths (EWs) of the most prominent absorption features in GRB afterglow spectra, providing the means to compare individual spectra to the sample and identify its peculiarities. Methods: Using 69 low-resolution GRB afterglow spectra, we conduct a study of the rest-frame EWs distribution of features with an average rest-frame EW larger than 0.5 Å. To compare an individual GRB with the sample, we develop EW diagrams as a graphical tool, and we give a catalogue with diagrams for the 69 spectra. We introduce a line strength parameter (LSP) that allows us to quantify the strength of the absorption features in a GRB spectrum as compared to the sample by a single number. Using the distributions of EWs of single-species features, we derive the distribution of their column densities by a curve of growth (CoG) fit. Results: We find correlations between the LSP and the extinction of the GRB, the UV brightness of the host galaxies and the neutral hydrogen column density. However, we see no significant evolution of the LSP with the redshift. There is a weak correlation between the ionisation of the absorbers and the energy of the GRB, indicating that, either the GRB event is responsible for part of the ionisation, or that galaxies with high-ionisation media produce more energetic GRBs. Spectral features in GRB spectra are, on average, 2.5 times stronger than those seen in QSO intervening damped Lyman-α (DLA) systems and slightly more ionised. In particular we find a larger excess in the EW of C ivλλ1549 relative to QSO DLAs, which could be related to an excess of Wolf-Rayet stars in the environments of GRBs. From the CoG fitting we obtain an average number of components in the

  13. Anatomy of a dark burst - the afterglow of GRB 060108

    NASA Astrophysics Data System (ADS)

    Oates, S. R.; Mundell, C. G.; Piranomonte, S.; Page, K. L.; de Pasquale, M.; Monfardini, A.; Melandri, A.; Zane, S.; Guidorzi, C.; Malesani, D.; Gomboc, A.; Bannister, N.; Blustin, A. J.; Capalbi, M.; Carter, D.; D'Avanzo, P.; Kobayashi, S.; Krimm, H. A.; O'Brien, P. T.; Page, M. J.; Smith, R. J.; Steele, I. A.; Tanvir, N.

    2006-10-01

    We present a multiwavelength study of GRB 060108 - the 100th gamma-ray burst discovered by Swift. The X-ray flux and light curve (three segments plus a flare) detected with the X-ray Telescope are typical of Swift long bursts. We report the discovery of a faint optical afterglow detected in deep BVRi'-band imaging obtained with the Faulkes Telescope North beginning 2.75 min after the burst. The afterglow is below the detection limit of the Ultraviolet/Optical Telescope within 100 s of the burst, while is evident in K-band images taken with the United Kingdom Infrared Telescope 45 min after the burst. The optical light curve is sparsely sampled. Observations taken in the R and i' bands can be fitted either with a single power-law decay in flux, F(t) ~ t-α where α = 0.43 +/- 0.08, or with a two-segment light curve with an initial steep decay α1 < 0.88 +/- 0.2, flattening to a slope α2 ~ 0.31 +/- 0.12. A marginal evidence for rebrightening is seen in the i' band. Deep R-band imaging obtained ~12 d post-burst with the Very Large Telescope reveals a faint, extended object (R ~ 23.5mag) at the location of the afterglow. Although the brightness is compatible with the extrapolation of the slow decay with index α2, significant flux is likely due to a host galaxy. This implies that the optical light curve had a break before 12 d, akin to what observed in the X-rays. We derive the maximum photometric redshift z < 3.2 for GRB 060108. We find that the spectral energy distribution at 1000 s after the burst, from the optical to the X-ray range, is best fitted by a simple power law, Fν ~ ν-β, with βOX = 0.54 and a small amount of extinction. The optical to X-ray spectral index (βOX) confirms GRB 060108 to be one of the optically darkest bursts detected. Our observations rule out a high redshift as the reason for the optical faintness of GRB 060108. We conclude that a more likely explanation is a combination of an intrinsic optical faintness of the burst, a hard optical

  14. Dynamics and afterglow light curves of gamma-ray burst blast waves encountering a density bump or void

    SciTech Connect

    Uhm, Z. Lucas; Zhang, Bing E-mail: zhang@physics.unlv.edu

    2014-07-01

    We investigate the dynamics and afterglow light curves of gamma-ray burst blast waves that encounter various density structures (such as bumps, voids, or steps) in the surrounding ambient medium. We present and explain the characteristic response features that each type of density structure in the medium leaves on the forward shock (FS) and reverse shock (RS) dynamics for blast waves with either a long-lived or short-lived RS. We show that when the ambient medium density drops, the blast waves exhibit in some cases a period of an actual acceleration (even during their deceleration stage) due to adiabatic cooling of blast waves. Comparing numerical examples that have different shapes of bumps or voids, we propose a number of consistency tests that must be satisfied by correct modeling of blast waves. Our model results successfully pass these tests. Employing a Lagrangian description of blast waves, we perform a sophisticated calculation of afterglow emission. We show that as a response to density structures in the ambient medium, the RS light curves produce more significant variations than the FS light curves. Some observed features (such as rebrightenings, dips, or slow wiggles) can be more easily explained within the RS model. We also discuss the origin of these different features imprinted on the FS and RS light curves.

  15. Dynamics and Afterglow Light Curves of Gamma-Ray Burst Blast Waves Encountering a Density Bump or Void

    NASA Astrophysics Data System (ADS)

    Uhm, Z. Lucas; Zhang, Bing

    2014-07-01

    We investigate the dynamics and afterglow light curves of gamma-ray burst blast waves that encounter various density structures (such as bumps, voids, or steps) in the surrounding ambient medium. We present and explain the characteristic response features that each type of density structure in the medium leaves on the forward shock (FS) and reverse shock (RS) dynamics for blast waves with either a long-lived or short-lived RS. We show that when the ambient medium density drops, the blast waves exhibit in some cases a period of an actual acceleration (even during their deceleration stage) due to adiabatic cooling of blast waves. Comparing numerical examples that have different shapes of bumps or voids, we propose a number of consistency tests that must be satisfied by correct modeling of blast waves. Our model results successfully pass these tests. Employing a Lagrangian description of blast waves, we perform a sophisticated calculation of afterglow emission. We show that as a response to density structures in the ambient medium, the RS light curves produce more significant variations than the FS light curves. Some observed features (such as rebrightenings, dips, or slow wiggles) can be more easily explained within the RS model. We also discuss the origin of these different features imprinted on the FS and RS light curves.

  16. Hidden in the light: Magnetically induced afterglow from trapped chameleon fields

    NASA Astrophysics Data System (ADS)

    Gies, Holger; Mota, David F.; Shaw, Douglas J.

    2008-01-01

    We propose an afterglow phenomenon as a unique trace of chameleon fields in optical experiments. The vacuum interaction of a laser pulse with a magnetic field can lead to a production and subsequent trapping of chameleons in the vacuum chamber, owing to their mass dependence on the ambient matter density. Magnetically induced reconversion of the trapped chameleons into photons creates an afterglow over macroscopic timescales that can conveniently be searched for by current optical experiments. We show that the chameleon parameter range accessible to available laboratory technology is comparable to scales familiar from astrophysical stellar energy-loss arguments. We analyze quantitatively the afterglow properties for various experimental scenarios and discuss the role of potential background and systematic effects. We conclude that afterglow searches represent an ideal tool to aim at the production and detection of cosmologically relevant scalar fields in the laboratory.

  17. Determination of hexabromocyclododecane by flowing atmospheric pressure afterglow mass spectrometry.

    PubMed

    Smoluch, Marek; Silberring, Jerzy; Reszke, Edward; Kuc, Joanna; Grochowalski, Adam

    2014-10-01

    The first application of a flowing atmospheric-pressure afterglow ion source for mass spectrometry (FAPA-MS) for the chemical characterization and determination of hexabromocyclododecane (HBCD) is presented. The samples of technical HBCD and expanded polystyrene foam (EPS) containing HBCD as a flame retardant were prepared by dissolving the appropriate solids in dichloromethane. The ionization of HBCD was achieved with a prototype FAPA source. The ions were detected in the negative-ion mode. The ions corresponding to a deprotonated HBCD species (m/z 640.7) as well as chlorine (m/z 676.8), nitrite (m/z 687.8) and nitric (m/z 703.8) adducts were observed in the spectra. The observed isotope pattern is characteristic for a compound containing six bromine atoms. This technique is an effective approach to detect HBCD, which is efficiently ionized in a liquid phase, resulting in high detection efficiency and sensitivity. PMID:25059130

  18. Langmuir-Probe Measurements in Flowing-Afterglow Plasmas

    NASA Technical Reports Server (NTRS)

    Johnsen, R.; Shunko, E. V.; Gougousi, T.; Golde, M. F.

    1994-01-01

    The validity of the orbital-motion theory for cylindrical Langmuir probes immersed in flowing- afterglow plasmas is investigated experimentally. It is found that the probe currents scale linearly with probe area only for electron-collecting but not for ion-collecting probes. In general, no agreement is found between the ion and electron densities derived from the probe currents. Measurements in recombining plasmas support the conclusion that only the electron densities derived from probe measurements can be trusted to be of acceptable accuracy. This paper also includes a brief derivation of the orbital-motion theory, a discussion of perturbations of the plasma by the probe current, and the interpretation of plasma velocities obtained from probe measurements.

  19. Escherichia coli morphological changes and lipid A removal induced by reduced pressure nitrogen afterglow exposure.

    PubMed

    Zerrouki, Hayat; Rizzati, Virginie; Bernis, Corinne; Nègre-Salvayre, Anne; Sarrette, Jean Philippe; Cousty, Sarah

    2015-01-01

    Lipid A is a major hydrophobic component of lipopolysaccharides (endotoxin) present in the membrane of most Gram-negative bacteria, and the major responsible for the bioactivity and toxicity of the endotoxin. Previous studies have demonstrated that the late afterglow region of flowing post-discharges at reduced pressure (1-20 Torr) can be used for the sterilization of surfaces and of the reusable medical instrumentation. In the present paper, we show that the antibacterial activity of a pure nitrogen afterglow can essentially be attributed to the large concentrations of nitrogen atoms present in the treatment area and not to the UV radiation of the afterglow. In parallel, the time variation of the inactivation efficiency quantified by the log reduction of the initial Escherichia coli (E. coli) population is correlated with morphologic changes observed on the bacteria by scanning electron microscopy (SEM) for increasing afterglow exposure times. The effect of the afterglow exposure is also studied on pure lipid A and on lipid A extracted from exposed E. coli bacteria. We report that more than 60% of lipid A (pure or bacteria-extracted) are lost with the used operating conditions (nitrogen flow QN2 = 1 standard liter per minute (slpm), pressure p = 5 Torr, microwave injected power PMW = 200 W, exposure time: 40 minutes). The afterglow exposure also results in a reduction of the lipid A proinflammatory activity, assessed by the net decrease of the redox-sensitive NFκB transcription factor nuclear translocation in murine aortic endothelial cells stimulated with control vs afterglow-treated (pure and extracted) lipid A. Altogether these results point out the ability of reduced pressure nitrogen afterglows to neutralize the cytotoxic components in Gram-negative bacteria.

  20. Escherichia coli Morphological Changes and Lipid A Removal Induced by Reduced Pressure Nitrogen Afterglow Exposure

    PubMed Central

    Zerrouki, Hayat; Rizzati, Virginie; Bernis, Corinne; Nègre-Salvayre, Anne; Sarrette, Jean Philippe; Cousty, Sarah

    2015-01-01

    Lipid A is a major hydrophobic component of lipopolysaccharides (endotoxin) present in the membrane of most Gram-negative bacteria, and the major responsible for the bioactivity and toxicity of the endotoxin. Previous studies have demonstrated that the late afterglow region of flowing post-discharges at reduced pressure (1-20 Torr) can be used for the sterilization of surfaces and of the reusable medical instrumentation. In the present paper, we show that the antibacterial activity of a pure nitrogen afterglow can essentially be attributed to the large concentrations of nitrogen atoms present in the treatment area and not to the UV radiation of the afterglow. In parallel, the time variation of the inactivation efficiency quantified by the log reduction of the initial Escherichia coli (E. coli) population is correlated with morphologic changes observed on the bacteria by scanning electron microscopy (SEM) for increasing afterglow exposure times. The effect of the afterglow exposure is also studied on pure lipid A and on lipid A extracted from exposed E. coli bacteria. We report that more than 60% of lipid A (pure or bacteria-extracted) are lost with the used operating conditions (nitrogen flow QN2 = 1 standard liter per minute (slpm), pressure p = 5 Torr, microwave injected power PMW = 200 W, exposure time: 40 minutes). The afterglow exposure also results in a reduction of the lipid A proinflammatory activity, assessed by the net decrease of the redox-sensitive NFκB transcription factor nuclear translocation in murine aortic endothelial cells stimulated with control vs afterglow-treated (pure and extracted) lipid A. Altogether these results point out the ability of reduced pressure nitrogen afterglows to neutralize the cytotoxic components in Gram-negative bacteria. PMID:25837580

  1. iPTF14yb: The First Discovery of a Gamma-Ray Burst Afterglow Independent of a High-Energy Trigger

    DOE PAGES

    Cenko, S. Bradley; Urban, Alex L.; Perley, Daniel A.; Horesh, Assaf; Corsi, Alessandra; Fox, Derek B.; Cao, Yi; Kasliwal, Mansi M.; Lien, Amy; Arcavi, Iair; et al

    2015-04-20

    We report here the discovery by the Intermediate Palomar Transient Factory (iPTF) of iPTF14yb, a luminous (Msub>r ≈ ₋27.8 mag), cosmological (redshift 1.9733), rapidly fading optical transient. We demonstrate, based on probabilistic arguments and a comparison with the broader population, that iPTF14yb is the optical afterglow of the long-duration gamma-ray burst GRB140226A. This marks the rst unambiguous discovery of a GRB afterglow prior to (and thus entirely independent of) an associated high-energy trigger. We estimate the rate of iPTF14yb-like sources (i.e., cosmologically dis- tant relativistic explosions) based on iPTF observations, inferring an all-sky value ofmore » $$R_{rel}$$ = 610yr-1 (68% con dence interval of 110{2000 yr-1). Our derived rate is consistent (within the large uncer- tainty) with the all-sky rate of on-axis GRBs derived by the Swift satellite. Finally, we brie y discuss the implications of the nondetection to date of bona de \\orphan" afterglows (i.e., those lacking de- tectable high-energy emission) on GRB beaming and the degree of baryon loading in these relativistic jets.« less

  2. iPTF14yb: The First Discovery of a Gamma-Ray Burst Afterglow Independent of a High-Energy Trigger

    SciTech Connect

    Cenko, S. Bradley; Urban, Alex L.; Perley, Daniel A.; Horesh, Assaf; Corsi, Alessandra; Fox, Derek B.; Cao, Yi; Kasliwal, Mansi M.; Lien, Amy; Arcavi, Iair; Bloom, Joshua S.; Butler, Nat R.; Cucchiara, Antonino; Diego, José A. de; Filippenko, Alexei V.; Gal-Yam, Avishay; Gehrels, Neil; Georgiev, Leonid; Gonzalez, J. Jesus; Graham, John F.; Greiner, Jochen; Kann, D. Alexander; Klein, Christopher R.; Knust, Fabian; Kulkarni, S. R.; Kutyrev, Alexander; Laher, Russ; Lee, William H.; Nugent, Peter E.; Xavier Prochaska, J.; Rubin, Adam; Urata, Yuji; Varela, Karla; Watson, Alan M.; Wozniak, Przemek R.

    2015-04-20

    We report here the discovery by the Intermediate Palomar Transient Factory (iPTF) of iPTF14yb, a luminous (Msub>r ≈ ₋27.8 mag), cosmological (redshift 1.9733), rapidly fading optical transient. We demonstrate, based on probabilistic arguments and a comparison with the broader population, that iPTF14yb is the optical afterglow of the long-duration gamma-ray burst GRB140226A. This marks the rst unambiguous discovery of a GRB afterglow prior to (and thus entirely independent of) an associated high-energy trigger. We estimate the rate of iPTF14yb-like sources (i.e., cosmologically dis- tant relativistic explosions) based on iPTF observations, inferring an all-sky value of $R_{rel}$ = 610yr-1 (68% con dence interval of 110{2000 yr-1). Our derived rate is consistent (within the large uncer- tainty) with the all-sky rate of on-axis GRBs derived by the Swift satellite. Finally, we brie y discuss the implications of the nondetection to date of bona de \\orphan" afterglows (i.e., those lacking de- tectable high-energy emission) on GRB beaming and the degree of baryon loading in these relativistic jets.

  3. iPTF14yb: The First Discovery of a Gamma-Ray Burst Afterglow Independent of a High-Energy Trigger

    NASA Technical Reports Server (NTRS)

    Cenko, S. Bradley; Urban, Alex L.; Perley, Daniel A.; Horesh, Assaf; Corsi, Alessandra; Fox, Derek B.; Cao, Yi; Kasliwal, Mansi M.; Lien, Amy; Arcavi, Iair; Bloom, Joshua S.; Butler, Nat R.; Cucchiara, Antonino; De Diego, Jose A.; Filippenko, Alexei V.; Gal-Yam, Avishay; Gehrels, Neil; Georgiev, Leonid; Gonzalez, J. Jesus; Graham, John F.; Greiner, Jochen; Kann, D. Alexander; Klein, Christopher R.; Knust, Fabian; Kutyrev, Alexander

    2015-01-01

    We report here the discovery by the Intermediate Palomar Transient Factory (iPTF) of iPTF14yb, a luminous (Mr >> -27.8 mag), cosmological (redshift 1.9733), rapidly fading optical transient. We demonstrate, based on probabilistic arguments and a comparison with the broader population, that iPTF14yb is the optical afterglow of the long-duration gamma-ray burst GRB 140226A. This marks the first unambiguous discovery of a GRB afterglow prior to (and thus entirely independent of) an associated high-energy trigger. We estimate the rate of iPTF14yb-like sources (i.e., cosmologically distant relativistic explosions) based on iPTF observations, inferring an all-sky value of Rrel = 610/yr (68% confidence interval of 110-2000/yr). Our derived rate is consistent (within the large uncertainty) with the all-sky rate of on-axis GRBs derived by the Swift satellite. Finally, we briefly discuss the implications of the nondetection to date of bona fide "orphan" afterglows (i.e., those lacking detectable high-energy emission) on GRB beaming and the degree of baryon loading in these relativistic jets.

  4. iPTF14yb: The First GRB Discovered Outside the Gamma-Ray Bandpass and the Rate of Orphan Afterglows

    NASA Astrophysics Data System (ADS)

    Cenko, Stephen

    2015-04-01

    We report here the discovery by the Intermediate Palomar Transient Factory (iPTF) of iPTF14yb, the first unambiguous detection of an afterglow-like transient identified outside the γ-ray bandpass. Subsequent to our discovery announcement, the ``parent'' γ-ray burst GRB 140226A was identified by the InterPlanetary Network of high-energy detectors. We demonstrate an association between iPTF14yb and GRB 140226A based both on probabilistic arguments and by comparing iPTF14yb with the known population of long GRB afterglows and host galaxies. We furthermore estimate the rate of iPTF14yb-like transients based on iPTF observations, and demonstrate it is consistent with the rate of on-axis long GRBs. Finally, we briefly discuss the implications of the non-detection to date of bona fide ``orphan'' afterglows (i.e., those lacking entirely in high-energy emission) on GRB beaming and the degree of baryon loading in these relativistic jets.

  5. iPTF14yb: The First Discovery of a Gamma-Ray Burst Afterglow Independent of a High-energy Trigger

    NASA Astrophysics Data System (ADS)

    Cenko, S. Bradley; Urban, Alex L.; Perley, Daniel A.; Horesh, Assaf; Corsi, Alessandra; Fox, Derek B.; Cao, Yi; Kasliwal, Mansi M.; Lien, Amy; Arcavi, Iair; Bloom, Joshua S.; Butler, Nat R.; Cucchiara, Antonino; de Diego, José A.; Filippenko, Alexei V.; Gal-Yam, Avishay; Gehrels, Neil; Georgiev, Leonid; Jesús González, J.; Graham, John F.; Greiner, Jochen; Kann, D. Alexander; Klein, Christopher R.; Knust, Fabian; Kulkarni, S. R.; Kutyrev, Alexander; Laher, Russ; Lee, William H.; Nugent, Peter E.; Prochaska, J. Xavier; Ramirez-Ruiz, Enrico; Richer, Michael G.; Rubin, Adam; Urata, Yuji; Varela, Karla; Watson, Alan M.; Wozniak, Przemek R.

    2015-04-01

    We report here the discovery by the Intermediate Palomar Transient Factory (iPTF) of iPTF14yb, a luminous ({{M}r}≈ -27.8 mag), cosmological (redshift 1.9733), rapidly fading optical transient. We demonstrate, based on probabilistic arguments and a comparison with the broader population, that iPTF14yb is the optical afterglow of the long-duration gamma-ray burst GRB 140226A. This marks the first unambiguous discovery of a GRB afterglow prior to (and thus entirely independent of) an associated high-energy trigger. We estimate the rate of iPTF14yb-like sources (i.e., cosmologically distant relativistic explosions) based on iPTF observations, inferring an all-sky value of {{\\Re }rel}=610 yr-1 (68% confidence interval of 110-2000 yr-1). Our derived rate is consistent (within the large uncertainty) with the all-sky rate of on-axis GRBs derived by the Swift satellite. Finally, we briefly discuss the implications of the nondetection to date of bona fide “orphan” afterglows (i.e., those lacking detectable high-energy emission) on GRB beaming and the degree of baryon loading in these relativistic jets.

  6. Long-lived plasma and fast quenching of N2(C3Π u ) by electrons in the afterglow of a nanosecond capillary discharge in nitrogen

    NASA Astrophysics Data System (ADS)

    Lepikhin, N. D.; Klochko, A. V.; Popov, N. A.; Starikovskaia, S. M.

    2016-08-01

    Quenching of electronically excited nitrogen state, {{\\text{N}}2}≤ft({{\\text{C}}3}{{\\Pi}u},{{v}\\prime}=0\\right) , in the afterglow of nanosecond capillary discharge in pure nitrogen is studied. It is found experimentally that an additional collisional mechanism appears and dominates at high specific deposited energies leading to the anomalously fast quenching of the {{\\text{N}}2}≤ft({{\\text{C}}3}{{\\Pi}u}\\right) in the afterglow. On the basis of obtained experimental data and of the analysis of possible quenching agents, it is concluded that the anomalously fast deactivation of the {{\\text{N}}2}≤ft({{\\text{C}}3}{{\\Pi}u}\\right) can be explained by quenching by electrons. Long-lived plasma at time scale of hundreds nanoseconds after the end of the pulse is observed. High electron densities, about 1014 cm‑3 at 27 mbar, are sustained by reactions of associative ionization. Kinetic 1D numerical modeling and comparison of calculated results with experimentally measured electric fields in the second high-voltage pulse 250 ns after the initial pulse, and electron density measurements in the afterglow confirm the validity of the suggested mechanism.

  7. THERMAL EMISSION IN THE EARLY X-RAY AFTERGLOWS OF GAMMA-RAY BURSTS: FOLLOWING THE PROMPT PHASE TO LATE TIMES

    SciTech Connect

    Friis, Mette; Watson, Darach E-mail: darach@dark-cosmology.dk

    2013-07-01

    Thermal radiation, peaking in soft X-rays, has now been detected in a handful of gamma-ray burst (GRB) afterglows and has to date been interpreted as shock break-out of the GRB's progenitor star. We present a search for thermal emission in the early X-ray afterglows of a sample of Swift bursts selected by their brightness in X-rays at early times. We identify a clear thermal component in eight GRBs and track the evolution. We show that at least some of the emission must come from highly relativistic material since two show an apparent super-luminal expansion of the thermal component. Furthermore, we determine very large luminosities and high temperatures for many of the components-too high to originate in a supernova shock break-out. Instead, we suggest that the component may be modeled as late photospheric emission from the jet, linking it to the apparently thermal component observed in the prompt emission of some GRBs at gamma-ray and hard X-ray energies. By comparing the parameters from the prompt emission and the early afterglow emission, we find that the results are compatible with the interpretation that we are observing the prompt quasi-thermal emission component in soft X-rays at a later point in its evolution.

  8. Long-lived plasma and fast quenching of N2(C3Π u ) by electrons in the afterglow of a nanosecond capillary discharge in nitrogen

    NASA Astrophysics Data System (ADS)

    Lepikhin, N. D.; Klochko, A. V.; Popov, N. A.; Starikovskaia, S. M.

    2016-08-01

    Quenching of electronically excited nitrogen state, {{\\text{N}}2}≤ft({{\\text{C}}3}{{\\Pi}u},{{v}\\prime}=0\\right) , in the afterglow of nanosecond capillary discharge in pure nitrogen is studied. It is found experimentally that an additional collisional mechanism appears and dominates at high specific deposited energies leading to the anomalously fast quenching of the {{\\text{N}}2}≤ft({{\\text{C}}3}{{\\Pi}u}\\right) in the afterglow. On the basis of obtained experimental data and of the analysis of possible quenching agents, it is concluded that the anomalously fast deactivation of the {{\\text{N}}2}≤ft({{\\text{C}}3}{{\\Pi}u}\\right) can be explained by quenching by electrons. Long-lived plasma at time scale of hundreds nanoseconds after the end of the pulse is observed. High electron densities, about 1014 cm-3 at 27 mbar, are sustained by reactions of associative ionization. Kinetic 1D numerical modeling and comparison of calculated results with experimentally measured electric fields in the second high-voltage pulse 250 ns after the initial pulse, and electron density measurements in the afterglow confirm the validity of the suggested mechanism.

  9. Sterilization/disinfection using reduced-pressure plasmas: some differences between direct exposure of bacterial spores to a discharge and their exposure to a flowing afterglow

    NASA Astrophysics Data System (ADS)

    Moisan, M.; Levif, P.; Séguin, J.; Barbeau, J.

    2014-07-01

    The use of plasma for sterilization or disinfection offers a promising alternative to conventional steam or chemical approaches. Plasma can operate at temperatures less damaging to some heat-sensitive medical devices and, in contrast to chemicals, can be non-toxic and non-polluting for the operator and the environment, respectively. Direct exposure to the gaseous discharge (comprising an electric field and ions/electrons) or exposure to its afterglow (no E-field) can both be envisaged a priori, since these two methods can achieve sterility. However, important issues must be considered besides the sterility goal. Direct exposure to the discharge, although yielding a faster inactivation of microorganisms, is shown to be potentially more aggressive to materials and sometimes subjected to the shadowing effect that precludes the sterilization of complex-form items. These two drawbacks can be successfully minimized with an adequate flowing-afterglow exposure. Most importantly, the current paper shows that direct exposure to the discharge can lead to the dislodgment and release of viable microorganisms from their substratum. Such a phenomenon could be responsible for the recontamination of sterilized devices as well as possible contamination of the ambient surroundings, additionally yielding an erroneous over-appreciation of the inactivation efficiency. The operation of the N2-O2 flowing afterglow system being developed in our group is such that there are no ions and electrons left in the process chamber (late-afterglow regime) in full contrast with their presence in the discharge. The dislodgment and release of spores could be attributed, based on the literature, to their electrostatic charging by electrons, leading to an (outward) electrostatic stress that exceeds the adhesion of the spores on their substrate.

  10. An Achromatic Break in the Afterglow of the Short GRB 140903A: Evidence for a Narrow Jet

    NASA Astrophysics Data System (ADS)

    Troja, E.; Sakamoto, T.; Cenko, S. B.; Lien, A.; Gehrels, N.; Castro-Tirado, A. J.; Ricci, R.; Capone, J.; Toy, V.; Kutyrev, A.; Kawai, N.; Cucchiara, A.; Fruchter, A.; Gorosabel, J.; Jeong, S.; Levan, A.; Perley, D.; Sanchez-Ramirez, R.; Tanvir, N.; Veilleux, S.

    2016-08-01

    We report the results of our observing campaign on GRB 140903A, a nearby (z = 0.351) short-duration (T 90 ˜ 0.3 s) gamma-ray burst discovered by Swift. We monitored the X-ray afterglow with Chandra up to 15 days after the burst and detected a steeper decay of the X-ray flux after t j ≈ 1 day. Continued monitoring at optical and radio wavelengths showed a similar decay in flux at nearly the same time, and we interpret it as evidence of a narrowly collimated jet. By using the standard fireball model to describe the afterglow evolution, we derive a jet opening angle θ j ≈ 5° and a collimation-corrected total energy release E ≈ 2 × {10}50 erg. We further discuss the nature of the GRB progenitor system. Three main lines disfavor a massive star progenitor: the properties of the prompt gamma-ray emission, the age and low star formation rate of the host galaxy, and the lack of a bright supernova. We conclude that this event likely originated from a compact binary merger.

  11. Model-based software design

    NASA Technical Reports Server (NTRS)

    Iscoe, Neil; Liu, Zheng-Yang; Feng, Guohui; Yenne, Britt; Vansickle, Larry; Ballantyne, Michael

    1992-01-01

    Domain-specific knowledge is required to create specifications, generate code, and understand existing systems. Our approach to automating software design is based on instantiating an application domain model with industry-specific knowledge and then using that model to achieve the operational goals of specification elicitation and verification, reverse engineering, and code generation. Although many different specification models can be created from any particular domain model, each specification model is consistent and correct with respect to the domain model.

  12. Model-Based Reasoning

    ERIC Educational Resources Information Center

    Ifenthaler, Dirk; Seel, Norbert M.

    2013-01-01

    In this paper, there will be a particular focus on mental models and their application to inductive reasoning within the realm of instruction. A basic assumption of this study is the observation that the construction of mental models and related reasoning is a slowly developing capability of cognitive systems that emerges effectively with proper…

  13. Principles of models based engineering

    SciTech Connect

    Dolin, R.M.; Hefele, J.

    1996-11-01

    This report describes a Models Based Engineering (MBE) philosophy and implementation strategy that has been developed at Los Alamos National Laboratory`s Center for Advanced Engineering Technology. A major theme in this discussion is that models based engineering is an information management technology enabling the development of information driven engineering. Unlike other information management technologies, models based engineering encompasses the breadth of engineering information, from design intent through product definition to consumer application.

  14. Ambient magnetic field amplification in shock fronts of relativistic jets: an application to GRB afterglows

    NASA Astrophysics Data System (ADS)

    Rocha da Silva, G.; Falceta-Gonçalves, D.; Kowal, G.; de Gouveia Dal Pino, E. M.

    2015-01-01

    Strong downstream magnetic fields of the order of ˜1 G, with large correlation lengths, are believed to cause the large synchrotron emission at the afterglow phase of gamma-ray bursts (GRBs). Despite the recent theoretical efforts, models have failed to fully explain the amplification of the magnetic field, particularly in a matter-dominated scenario. We revisit the problem by considering the synchrotron emission to occur at the expanding shock front of a weakly magnetized relativistic jet over a magnetized surrounding medium. Analytical estimates and a number of high-resolution 2D relativistic magnetohydrodynamical (RMHD) simulations are provided. Jet opening angles of θ = 0°-20°, and ambient to jet density ratios of 10-4-102 were considered. We found that most of the amplification is due to compression of the ambient magnetic field at the contact discontinuity between the reverse and forward shocks at the jet head, with substantial pile-up of the magnetic field lines as the jet propagates sweeping the ambient field lines. The pile-up is maximum for θ → 0, decreasing with θ, but larger than in the spherical blast problem. Values obtained for certain models are able to explain the observed intensities. The maximum correlation lengths found for such strong fields is of lcorr ≤ 1014 cm, 2-6 orders of magnitude larger than the found in previous works.

  15. Experimental and numerical studies on Xe2* VUV emission in fast electric discharge afterglow

    NASA Astrophysics Data System (ADS)

    Lo, Dennis; Shangguan, Cheng; Kochetov, Igor; Napartovich, Anatoly

    2002-10-01

    Optical and electrical properties of a fast ( 50 ns) high-pressure discharge in pure Xe and Xe-Ne mixtures were studied experimentally and simulated numerically. Afterglow VUV emission was revealed lasting for a few microseconds. Its duration depended on gas pressure and Xe content. Observations of VUV emission intensity across the discharge aperture demonstrated a good uniformity with sizes 4.5x 2 mm2. The length of the discharge was 42 cm. Operation of the discharge was limited in gas pressure by development of instability. The highest pressure for stable discharge run was 0.55 bar for pure Xe and 5 bar for xenon-lean mixture. A detailed kinetic model of discharge plasma was developed, which calculated self-consistently electron energy distribution function and excited states including excimer population dynamics. VUV emission dynamics observed experimentally can be explained theoretically only in a model with an essentially increased number of electronic states taken into account. Calculated discharge voltage history and VUV emission dynamics agree satisfactory with measurements.

  16. NO FLARES FROM GAMMA-RAY BURST AFTERGLOW BLAST WAVES ENCOUNTERING SUDDEN CIRCUMBURST DENSITY CHANGE

    SciTech Connect

    Gat, Ilana; Van Eerten, Hendrik; MacFadyen, Andrew

    2013-08-10

    Afterglows of gamma-ray bursts are observed to produce light curves with the flux following power-law evolution in time. However, recent observations reveal bright flares at times on the order of minutes to days. One proposed explanation for these flares is the interaction of a relativistic blast wave with a circumburst density transition. In this paper, we model this type of interaction computationally in one and two dimensions, using a relativistic hydrodynamics code with adaptive mesh refinement called RAM, and analytically in one dimension. We simulate a blast wave traveling in a stellar wind environment that encounters a sudden change in density, followed by a homogeneous medium, and compute the observed radiation using a synchrotron model. We show that flares are not observable for an encounter with a sudden density increase, such as a wind termination shock, nor for an encounter with a sudden density decrease. Furthermore, by extending our analysis to two dimensions, we are able to resolve the spreading, collimation, and edge effects of the blast wave as it encounters the change in circumburst medium. In all cases considered in this paper, we find that a flare will not be observed for any of the density changes studied.

  17. AFTERGLOW OBSERVATIONS OF FERMI LARGE AREA TELESCOPE GAMMA-RAY BURSTS AND THE EMERGING CLASS OF HYPER-ENERGETIC EVENTS

    SciTech Connect

    Cenko, S. B.; Butler, N. R.; Cobb, B. E.; Cucchiara, A.; Bloom, J. S.; Perley, D. A.; Filippenko, A. V.; Frail, D. A.; Harrison, F. A.; Haislip, J. B.; Reichart, D. E.; Ivarsen, K. M.; LaCluyze, A. P.; Berger, E.; Chandra, P.; Fox, D. B.; Prochaska, J. X.; Kasliwal, M. M.; Kulkarni, S. R.

    2011-05-01

    We present broadband (radio, optical, and X-ray) light curves and spectra of the afterglows of four long-duration gamma-ray bursts (GRBs; GRBs 090323, 090328, 090902B, and 090926A) detected by the Gamma-Ray Burst Monitor and Large Area Telescope (LAT) instruments on the Fermi satellite. With its wide spectral bandpass, extending to GeV energies, Fermi is sensitive to GRBs with very large isotropic energy releases (10{sup 54} erg). Although rare, these events are particularly important for testing GRB central-engine models. When combined with spectroscopic redshifts, our afterglow data for these four events are able to constrain jet collimation angles, the density structure of the circumburst medium, and both the true radiated energy release and the kinetic energy of the outflows. In agreement with our earlier work, we find that the relativistic energy budget of at least one of these events (GRB 090926A) exceeds the canonical value of 10{sup 51} erg by an order of magnitude. Such energies pose a severe challenge for models in which the GRB is powered by a magnetar or a neutrino-driven collapsar, but remain compatible with theoretical expectations for magnetohydrodynamical collapsar models (e.g., the Blandford-Znajek mechanism). Our jet opening angles ({theta}) are similar to those found for pre-Fermi GRBs, but the large initial Lorentz factors ({Gamma}{sub 0}) inferred from the detection of GeV photons imply {theta}{Gamma}{sub 0} {approx} 70-90, values which are above those predicted in magnetohydrodynamic models of jet acceleration. Finally, we find that these Fermi-LAT events preferentially occur in a low-density circumburst environment, and we speculate that this might result from the lower mass-loss rates of their lower-metallicity progenitor stars. Future studies of Fermi-LAT afterglows at radio wavelengths with the order-of-magnitude improvement in sensitivity offered by the Extended Very Large Array should definitively establish the relativistic energy

  18. SFT based cosmological models

    NASA Astrophysics Data System (ADS)

    Koshelev, Alexey S.

    2010-11-01

    We consider the appearance of multiple scalar fields in SFT inspired non-local models with a single scalar field at late times. In this regime all the scalar fields are free. This system minimally coupled to gravity is mainly analyzed in this note. We build one exact solution to the equations of motion. We consider an exactly solvable model which obeys a simple exact solution in the cosmological context for the Friedmann equations and that reproduces the behavior expected from SFT in the asymptotic regime.

  19. Active species in N2 and N2-O2 afterglows for surface treatments

    NASA Astrophysics Data System (ADS)

    Ricard, A.; Pointu, A. M.; Villeger, S.; Canal, C.

    2010-01-01

    Production of active species is studied in N2 and in N2-O2 afterglows of electrical discharges at low and atmospheric gas pressures. They are produced in microwave discharges in a large range of gas pressures from a few Torr to 100 Torr and in corona discharges at atmospheric gas pressure. The active species in N2 afterglows are the N-atoms which are in the range of a few percents in the afterglows. The effect of O2 molecules in low percentages in low pressure N2microwave plasmas and as impurity in corona N2 discharges is specially analysed. The interaction of N and O-atoms with surfaces is studied for bacteria decontamination and for transmission of N-atoms though porous membranes. The processes of bacteria decontamination in N2-O2 afterglows are described for low pressure microwave and atmospheric pressure corona discharges. Transmission of N-atoms through porous membranes is studied at medium pressure (10-100 Torr) microwave afterglows.

  20. A Decade of Short-duration Gamma-ray Burst Afterglows

    NASA Astrophysics Data System (ADS)

    Fong, Wen-fai

    2014-10-01

    The afterglows of gamma-ray bursts (GRBs) provide a unique way to study the explosion properties and sub-parsec environments of these catastrophic events. Indeed, observational campaigns to characterize the afterglows of long GRBs (duration > 2 sec) have lent crucial insight to their massive star progenitors. Short GRBs, which are linked to the mergers of two compact objects, are discovered at a significantly lower rate and have faint afterglows, thus making an understanding of their basic explosion properties more challenging. In this talk, I describe an observational campaign to characterize the afterglows of short GRBs over the past decade, spanning radio to X-ray wavelengths. I use the temporal and spectral behavior of their afterglows to quantify their kinetic energy scales, circumburst densities, and jet opening angles for the first time. I explore any trends between these explosion properties and their host galaxies. Finally, since compact object mergers are the premier candidates for Advanced LIGO detection, I assess the implications for electromagnetic counterparts to gravitational waves.

  1. Rule-based simulation models

    NASA Technical Reports Server (NTRS)

    Nieten, Joseph L.; Seraphine, Kathleen M.

    1991-01-01

    Procedural modeling systems, rule based modeling systems, and a method for converting a procedural model to a rule based model are described. Simulation models are used to represent real time engineering systems. A real time system can be represented by a set of equations or functions connected so that they perform in the same manner as the actual system. Most modeling system languages are based on FORTRAN or some other procedural language. Therefore, they must be enhanced with a reaction capability. Rule based systems are reactive by definition. Once the engineering system has been decomposed into a set of calculations using only basic algebraic unary operations, a knowledge network of calculations and functions can be constructed. The knowledge network required by a rule based system can be generated by a knowledge acquisition tool or a source level compiler. The compiler would take an existing model source file, a syntax template, and a symbol table and generate the knowledge network. Thus, existing procedural models can be translated and executed by a rule based system. Neural models can be provide the high capacity data manipulation required by the most complex real time models.

  2. Shocked by the Very Bright Radio Flare and Afterglow of GRB 130427A

    NASA Astrophysics Data System (ADS)

    van der Horst, Alexander J.

    2014-01-01

    Gamma-ray burst (GRB) 130427A was extremely bright across the electromagnetic spectrum, with emission spanning 16 orders of magnitude in observing frequency, from almost 100 GeV gamma-rays down to the GHz radio regime. While the intrinsic luminosity of this GRB was not extreme compared to other GRBs, it displayed the largest measured fluence of the last three decades due to its proximity with a redshift of 0.34. One of the most notable characteristics of this GRB was its bright radio emission, in particular the radio flare which has been observed only a few times in other GRBs and is usually attributed to the reverse shock moving back into the GRB jet. Here we present radio observations with unprecedented temporal coverage at three observing frequencies obtained with the Westerbork Synthesis Radio Telescope (WSRT) and the Arcminute Microkelvin Imager (AMI). AMI had the earliest radio detection at 8 hours after the initial flash of gamma-rays, catching the radio flare on the rise. The 12-hour WSRT observations in the first few days enabled a detailed study of the short time-scale behavior at radio wavelengths. Besides our observations of the radio flare and afterglow up to three months after the gamma-ray trigger, we present our results for modeling the radio light curves together with the broadband data set in various other wavelength regimes, enabling us to determine physical parameters of both the reverse and forward shock of this enigmatic GRB.

  3. X-RAY SPECTRAL COMPONENTS OBSERVED IN THE AFTERGLOW OF GRB 130925A

    SciTech Connect

    Bellm, Eric C.; Forster, Karl; Harrison, Fiona A.; Madsen, Kristin K.; Perley, Daniel A.; Rana, Vikram R.; Barrière, Nicolas M.; Boggs, Steven E.; Craig, William W.; Bhalerao, Varun; Cenko, S. Bradley; Christensen, Finn E.; Fryer, Chris L.; Hailey, Charles J.; Horesh, Assaf; Ofek, Eran O.; Kouveliotou, Chryssa; Reynolds, Stephen P.; Stern, Daniel; and others

    2014-04-01

    We have identified spectral features in the late-time X-ray afterglow of the unusually long, slow-decaying GRB 130925A using NuSTAR, Swift/X-Ray Telescope, and Chandra. A spectral component in addition to an absorbed power law is required at >4σ significance, and its spectral shape varies between two observation epochs at 2 × 10{sup 5} and 10{sup 6} s after the burst. Several models can fit this additional component, each with very different physical implications. A broad, resolved Gaussian absorption feature of several keV width improves the fit, but it is poorly constrained in the second epoch. An additive blackbody or second power-law component provide better fits. Both are challenging to interpret: the blackbody radius is near the scale of a compact remnant (10{sup 8} cm), while the second power-law component requires an unobserved high-energy cutoff in order to be consistent with the non-detection by Fermi/Large Area Telescope.

  4. SHOCK CORRUGATION BY RAYLEIGH-TAYLOR INSTABILITY IN GAMMA-RAY BURST AFTERGLOW JETS

    SciTech Connect

    Duffell, Paul C.; MacFadyen, Andrew I. E-mail: macfadyen@nyu.edu

    2014-08-10

    Afterglow jets are Rayleigh-Taylor unstable and therefore turbulent during the early part of their deceleration. There are also several processes which actively cool the jet. In this Letter, we demonstrate that if cooling significantly increases the compressibility of the flow, the turbulence collides with the forward shock, destabilizing and corrugating it. In this case, the forward shock is turbulent enough to produce the magnetic fields responsible for synchrotron emission via small-scale turbulent dynamo. We calculate light curves assuming the magnetic field is in energy equipartition with the turbulent kinetic energy and discover that dynamic magnetic fields are well approximated by a constant magnetic-to-thermal energy ratio of 1%, though there is a sizeable delay in the time of peak flux as the magnetic field turns on only after the turbulence has activated. The reverse shock is found to be significantly more magnetized than the forward shock, with a magnetic-to-thermal energy ratio of the order of 10%. This work motivates future Rayleigh-Taylor calculations using more physical cooling models.

  5. X-Ray Spectral Components Observed in the Afterglow of GRB 130925A

    NASA Technical Reports Server (NTRS)

    Bellm, Eric C.; Barriere, Nicolas M.; Bhalerao, Varun; Boggs, Steven E.; Cenko, S. Bradley; Christensen, Finn E.; Craig, William W.; Forster, Karl; Fryer, Chris L.; Hailey, Charles J.; Harrison, Fiona A.; Horesh, Assaf; Kouveliotou, Chryssa; Madsen, Kristin K.; Miller, Jon M.; Ofek, Eran O.; Perley, Daniel A.; Rana, Vikram R.; Miller, Jon M.; Stern, Daniel; Tomsick, John A.; Zhang, William W.

    2014-01-01

    We have identified spectral features in the late-time X-ray afterglow of the unusually long, slow-decaying GRB 130925A using NuSTAR, Swift/X-Ray Telescope, and Chandra. A spectral component in addition to an absorbed power law is required at greater than 4 less than 1 significance, and its spectral shape varies between two observation epochs at 2 x 10 (sup 5) and 10 (sup 6) seconds after the burst. Several models can fit this additional component, each with very different physical implications. A broad, resolved Gaussian absorption feature of several kiloelectronvolts width improves the fit, but it is poorly constrained in the second epoch. An additive blackbody or second power-law component provide better fits. Both are challenging to interpret: the blackbody radius is near the scale of a compact remnant (10 (sup 8) centimeters), while the second power-law component requires an unobserved high-energy cutoff in order to be consistent with the non-detection by Fermi/Large Area Telescope.

  6. Probe measurements of penning electron spectra in the afterglow of nonlocal helium microplasma

    NASA Astrophysics Data System (ADS)

    Kudryavtsev, Anatoly; Belskiy, Denis; Gutsev, Sergey; Kosykh, Nikolay; Kryukov, Anton

    2012-10-01

    Method PLES [Blagoev A.B., Kolokolov, N.B., Kudryavtsev. Physica Scripta, 1994, v.50, p.371] is based on identification of atoms and molecules of impurities M by selective registration of groups of fast electrons e(f) created in Penning ionization: He(m) + M -> He +M+ + e(f). The electron energy spectrum e(f) contains discrete peaks corresponding to the difference between the energy 19.8 eV of metastable helium atoms He(m) and the ionization energies Ei of impurities M. Since the ionization potential Ei of each type of atom or molecule is a well-known, it is possible to identify the atoms or molecules M of the unknown impurity by their ionization potential Ei. Probe registration of the energy spectra of penning electrons is carried out in the nonlocal afterglow plasma of pulsed microdischarge in helium and its mixtures with argon, krypton and air. In helium, the non-local plasma condition corresponds to p xL < 5 Torr x cm, where p is the gas pressure and L is the plasma volume size. It is demonstrated that the obtained maxima appear at the characteristic energies corresponding exactly to the expected maxima for penning electrons of the known gas impurities used.

  7. Prompt and Afterglow Emission Properties of Gamma-Ray Bursts with Spectroscopically Identified Supernovae

    NASA Technical Reports Server (NTRS)

    Kaneko, Yuki; Ramirez-Ruiz, Enrico; Granot, Jonathan; Kouveliotou, Chryssa; Woosley, Stan E.; Patel, Sandeep K.; Rol, Evert; In'TZand, Jean J. M.; VanDerHorst, Alexander J.; Wuers, Ralph A. M. J.; Strom, Richard

    2007-01-01

    We present a detailed spectral analysis of the prompt and afterglow emission of four nearby long-soft gamma-ray bursts (GRBs 980425,030329,031203, and 060218) that were spectroscopically found to be associated with Type Ic supernovae and compare them to the general GRB population. For each event, we investigate the spectral and luminosity evolution and estimate the total energy budget based on broadband observations. The observational inventory for these events has become rich enough to allow estimates of their energy content in relativistic and subrelativistic form. The result is a global portrait of the effects of the physical processes responsible for producing long-soft GRBs. In particular, we find that the values of the energy released in mildly relativistic outflows appears to have a significantly smaller scatter than those found in highly relativistic ejecta. This is consistent with a picture in which the energy released inside the progenitor star is roughly standard, while the fraction of that energy that ends up in highly relativistic ejecta outside the star can vary dramatically between different events.

  8. Probing the Environment of Gravitational-wave Transient Sources with TeV Afterglow Emission

    NASA Astrophysics Data System (ADS)

    Zhu, Qin-Yu; Wang, Xiang-Yu

    2016-09-01

    Recently, the Advanced Laser Interferometer Gravitational-wave Observatory detected gravitational-wave (GW) transients from mergers of binary black holes (BHs). The system may also produce a wide-angle, relativistic outflow if the claimed short gamma-ray burst detected by GBM is in real association with GW150914. It was suggested that mergers of double neutron stars (or neutron star-black hole binaries), another promising source of GW transients, also produce fast, wide-angle outflows. In this paper, we calculate the high-energy gamma-ray emission arising from the blast waves driven by these wide-angle outflows. We find that TeV emission arising from the inverse-Compton process in the relativistic outflow, originating from mergers of binary BHs that are similar to those in GW150914, could be detectable by ground-based Imaging Atmospheric Cherenkov Telescopes such as the Cherenkov Telescope Array (CTA) if the sources occur in a dense medium with a density of n≳ 0.3 {{cm}}-3. For neutron star–neutron star (NS–NS) and NS–BH mergers, TeV emission from the wide-angle, mildly relativistic outflow could be detected as well, if it occurs in a dense medium with n≳ 10{--}100 {{cm}}-3. Thus, TeV afterglow emission could be a useful probe of the environment of the GW transients, which could shed light on the evolution channels of the progenitors of GW transients.

  9. Probing the Environment of Gravitational-wave Transient Sources with TeV Afterglow Emission

    NASA Astrophysics Data System (ADS)

    Zhu, Qin-Yu; Wang, Xiang-Yu

    2016-09-01

    Recently, the Advanced Laser Interferometer Gravitational-wave Observatory detected gravitational-wave (GW) transients from mergers of binary black holes (BHs). The system may also produce a wide-angle, relativistic outflow if the claimed short gamma-ray burst detected by GBM is in real association with GW150914. It was suggested that mergers of double neutron stars (or neutron star-black hole binaries), another promising source of GW transients, also produce fast, wide-angle outflows. In this paper, we calculate the high-energy gamma-ray emission arising from the blast waves driven by these wide-angle outflows. We find that TeV emission arising from the inverse-Compton process in the relativistic outflow, originating from mergers of binary BHs that are similar to those in GW150914, could be detectable by ground-based Imaging Atmospheric Cherenkov Telescopes such as the Cherenkov Telescope Array (CTA) if the sources occur in a dense medium with a density of n≳ 0.3 {{cm}}-3. For neutron star-neutron star (NS-NS) and NS-BH mergers, TeV emission from the wide-angle, mildly relativistic outflow could be detected as well, if it occurs in a dense medium with n≳ 10{--}100 {{cm}}-3. Thus, TeV afterglow emission could be a useful probe of the environment of the GW transients, which could shed light on the evolution channels of the progenitors of GW transients.

  10. Prompt and Afterglow Emission Properties of Gamma-Ray Bursts with Spectroscopically Identified Supernovae

    SciTech Connect

    Kaneko, Yuki; Ramirez-Ruiz, E.; Granot, J.; Kouveliotou, C.; Woosley, S.E.; Patel, S.K.; Rol, E.; Zand, J.J.M.in't; a; Wijers, R.A.M.J.; Strom, R.; /USRA, Huntsville /Princeton, Inst. Advanced Study /UC, Santa Cruz /KIPAC, Menlo Park /NASA, Marshall /Leicester U. /SRON, Utrecht /Utrecht, Astron. Inst. /Amsterdam U., Astron. Inst. /NFRA, Dwingeloo

    2006-07-12

    We present a detailed spectral analysis of the prompt and afterglow emission of four nearby long-soft gamma-ray bursts (GRBs 980425, 030329, 031203, and 060218) that were spectroscopically found to be associated with type Ic supernovae, and compare them to the general GRB population. For each event, we investigate the spectral and luminosity evolution, and estimate the total energy budget based upon broadband observations. The observational inventory for these events has become rich enough to allow estimates of their energy content in relativistic and sub-relativistic form. The result is a global portrait of the effects of the physical processes responsible for producing long-soft GRBs. In particular, we find that the values of the energy released in mildly relativistic outflows appears to have a significantly smaller scatter than those found in highly relativistic ejecta. This is consistent with a picture in which the energy released inside the progenitor star is roughly standard, while the fraction of that energy that ends up in highly relativistic ejecta outside the star can vary dramatically between different events.

  11. Sterilization/disinfection of medical devices using plasma: the flowing afterglow of the reduced-pressure N2-O2 discharge as the inactivating medium

    NASA Astrophysics Data System (ADS)

    Moisan, Michel; Boudam, Karim; Carignan, Denis; Kéroack, Danielle; Levif, Pierre; Barbeau, Jean; Séguin, Jacynthe; Kutasi, Kinga; Elmoualij, Benaïssa; Thellin, Olivier; Zorzi, Willy

    2013-07-01

    Potential sterilization/disinfection of medical devices (MDs) is investigated using a specific plasma process developed at the Université de Montréal over the last decade. The inactivating medium of the microorganisms is the flowing afterglow of a reduced-pressure N2-O2 discharge, which provides, as the main biocidal agent, photons over a broad ultraviolet (UV) wavelength range. The flowing afterglow is considered less damaging to MDs than the discharge itself. Working at gas pressures in the 400—700 Pa range (a few torr) ensures, through species diffusion, the uniform filling of large volume chambers with the species outflowing from the discharge, possibly allowing batch processing within them. As a rule, bacterial endospores are used as bio-indicators (BI) to validate sterilization processes. Under the present operating conditions, Bacillus atrophaeus is found to be the most resistant one and is therefore utilized as BI. The current paper reviews the main experimental results concerning the operation and characterization of this sterilizer/disinfector, updating and completing some of our previously published papers. It uses modeling results as guidelines, which are particularly useful when the corresponding experimental data are not (yet) available, hopefully leading to more insight into this plasma afterglow system. The species flowing out of the N2-O2 discharge can be divided into two groups, depending on the time elapsed after they left the discharge zone as they move toward the chamber, namely the early afterglow and the late afterglow. The early flowing afterglow from a pure N2 discharge (also called pink afterglow) is known to be comprised of N2+ and N4+ ions. In the present N2-O2 mixture discharge, NO+ ions are additionally generated, with a lifetime that extends over a longer period than that of the nitrogen molecular ions. We shall suppose that the disappearance of the NO+ ions marks the end of the early afterglow regime, thereby stressing our intent

  12. Constraints on an Optical Afterglow and on Supernova Light Following the Short Burst GRB 050813

    NASA Technical Reports Server (NTRS)

    Ferrero, P.; Sanchez, S. F.; Kann, D. A.; Klose, S.; Greiner, J.; Gorosabel, J.; Hartmann, D. H.; Henden, A. A.; Moller, P.; Palazzi, E.; Rau, A.; Stecklum, B.; Castro-Tirado, A. J.; Fynbok J. P. U.; Hjorth, J.; Jakobsson, P.; Kouveliotou, C.; Masetti, N.; Pian, E.; Tanvir, N. R.; Wijers, R. A. M. J.

    2006-01-01

    We report early follow-up observations of the error box of the short burst 050813 using the telescopes at Calar Alto and at Observatorio Sierra Nevada (OSN), followed by deep VLT/FORS2 I-band observations obtained under very good seeing conditions 5.7 and 11.7 days after the event. No evidence for a GRB afterglow was found in our Calar Alto and OSN data, no rising supernova component was detected in our FORS2 images. A potential host galaxy can be identified in our FORS2 images, even though we cannot state with certainty its association with GRB 050813. IN any case, the optical afterglow of GRB 050813 was very faint, well in agreement with what is known so far about the optical properties of afterglows of short bursts. We conclude that all optical data are not in conflict with the interpretation that GRB 050813 was a short burst.

  13. The Case for Anisotropic Afterglow Efficiency Within Gamma-Ray Burst Jets

    SciTech Connect

    Eichler, David; Granot, Jonathan; /KIPAC, Menlo Park

    2005-10-05

    Early X-ray afterglows recently detected by Swift frequently show a phase of very shallow flux decay lasting from a few hundred seconds up to {approx} 10{sup 4} s, followed by a steeper, more familiar decay. We suggest that the flat early part of the light curve may be a combination of the decaying tail of the prompt emission and the delayed onset of the afterglow emission observed from viewing angles slightly outside the edge of the jet, as predicted previously. This would imply that a significant fraction of viewers have a very small external shock energy along their line of sight and a very high {gamma}-ray to kinetic energy ratio. The early flat phase in the afterglow light curve implies, according to this or other interpretations, a very large {gamma}-ray efficiency, typically {approx}> 90%, which is very difficult to produce by internal shocks.

  14. X-ray excited ZnS:Cu,Co afterglow nanoparticles for photodynamic activation

    NASA Astrophysics Data System (ADS)

    Ma, Lun; Zou, Xiaoju; Bui, Brian; Chen, Wei; Song, Kwang Hyun; Solberg, Timothy

    2014-07-01

    Copper and cobalt co-doped ZnS (ZnS:Cu,Co) afterglow nanoparticles were conjugated to photosensitizer tetrabromorhodamine-123 (TBrRh123) and efficient energy transfer from the nanoparticles to TBrRh123 was observed. In addition to their X-ray excited luminescence, the ZnS:Cu,Co nanoparticles also show long lasting afterglow, which continuously serve as a light source for photodynamic therapy (PDT) activation. Compared to TBrRh123 or ZnS:Cu,Co alone, the ZnS:Cu,Co-TBrRh123 conjugates show low dark toxicity but high X-ray induced toxicity to human prostate cancer cells. The results indicate that the ZnS:Cu,Co afterglow nanoparticles have a good potential for PDT activation.

  15. Revisiting the dispersion measure of fast radio bursts associated with gamma-ray burst afterglows

    SciTech Connect

    Yu, Yun-Wei

    2014-12-01

    Some fast radio bursts (FRBs) are expected to be associated with the afterglow emission of gamma-ray bursts (GRBs), while a short-lived, supermassive neutron star (NS) forms during the GRBs. I investigate the possible contributions to the dispersion measure (DM) of the FRBs from the GRB ejecta and the wind blown from the precollapsing NS. On the one hand, sometimes an internal X-ray plateau afterglow could be produced by the NS wind, which indicates that a great number of electron-positron pairs are carried by the wind. If the pair-generation radius satisfies a somewhat rigorous condition, the relativistic and dense wind would contribute a high DM to the associated FRB, which can be comparable to and even exceed the DM contributed by the intergalactic medium. On the other hand, if the wind only carries a Goldreich-Julian particle flux, its DM contribution would become negligible; meanwhile, the internal plateau afterglow would not appear. Alternatively, the FRB should be associated with a GRB afterglow produced by the GRB external shock, i.e., an energy-injection-caused shallow-decay afterglow or a normal single-power-law afterglow if the impulsive energy release of the GRB is high enough. In the latter case, the DM contributed by the high-mass GRB ejecta could be substantially important, in particular, for an environment of main-sequence stellar wind. In summary, a careful assessment on the various DM contributors could be required for the cosmological application of the expected FRB-GRB association. The future DM measurements of GRB-associated FRBs could provide a constraint on the physics of NS winds.

  16. Model based vibration monitoring

    SciTech Connect

    Esat, I.; Paya, B.; Badi, M.N.M.

    1996-11-01

    The principal source of vibratory excitation of gear system is the unsteady component of the relative angular motion of pair of meshing spur gears. This vibratory excitation is described by the transmission error. The transmission error present itself as a varying force at the contact point of the meshing gear teeth. The varying force is also influenced by the varying tooth stiffness due to change of orientation of teeth relative to each other, during the contact phase of each pair. Such a varying force produces both lateral and torsional excitation to the gear system. This paper presents analytical formulation of a simple two meshing spur gear system as a three mass system (18 DOF). The mathematical model also incorporates the analytical formulation of the tooth stiffness. The analytical results are compared with the experimental results. At this stage of analysis the procedure developed for handling the nonlinear influences of the tooth geometry is not fully implemented and the tooth stiffness taken as a constant value representing the average tooth stiffness. The comparison between the analytical and experimental results are encouraging as three main frequency obtained from FFT of the experimental results correlates very closely with the analytical results.

  17. THE AFTERGLOW AND ENVIRONMENT OF THE SHORT GRB 111117A

    SciTech Connect

    Margutti, R.; Berger, E.; Fong, W.; Zauderer, B. A.; Soderberg, A. M.; Milisavljevic, D.; Sanders, N.; Cenko, S. B.; Greiner, J.; Cucchiara, A.

    2012-09-01

    We present multi-wavelength observations of the afterglow of the short GRB 111117A, and follow-up observations of its host galaxy. From rapid optical and radio observations, we place limits of r {approx}> 25.5 mag at {delta}t Almost-Equal-To 0.55 days and F{sub {nu}}(5.8 GHz) {approx}< 18 {mu}Jy at {delta}t Almost-Equal-To 0.50 days, respectively. However, using a Chandra observation at {delta}t Almost-Equal-To 3.0 days we locate the absolute position of the X-ray afterglow to an accuracy of 0.''22 (1{sigma}), a factor of about six times better than the Swift/XRT position. This allows us to robustly identify the host galaxy and to locate the burst at a projected offset of 1.''25 {+-} 0.''20 from the host centroid. Using optical and near-IR observations of the host galaxy we determine a photometric redshift of z = 1.3{sup +0.3}{sub -0.2}, one of the highest for any short gamma-ray burst (GRB), leading to a projected physical offset for the burst of 10.5 {+-} 1.7 kpc, typical of previous short GRBs. At this redshift, the isotropic {gamma}-ray energy is E{sub {gamma},iso} Almost-Equal-To 3.0 Multiplication-Sign 10{sup 51} erg (rest-frame 23-2300 keV) with a peak energy of E{sub pk} Almost-Equal-To 850-2300 keV (rest-frame). In conjunction with the isotropic X-ray energy, GRB 111117A appears to follow our recently reported E{sub x,iso}-E{sub {gamma},iso}-E{sub pk} universal scaling. Using the X-ray data along with the optical and radio non-detections, we find that for a blastwave kinetic energy of E{sub K,iso} Almost-Equal-To E{sub {gamma},iso} erg, the circumburst density is n{sub 0} Almost-Equal-To 3 Multiplication-Sign 10{sup -4} - 1 cm{sup -3} (for a range of {epsilon}{sub B} = 0.001-0.1). Similarly, from the non-detection of a break in the X-ray light curve at {delta}t {approx}< 3 days, we infer a minimum opening angle for the outflow of {theta}{sub j} {approx}> 3-10 Degree-Sign (depending on the circumburst density). We conclude that Chandra observations of short

  18. Spin-Dependent Dissociative Excitation in a Laser Pumped Afterglow.

    NASA Astrophysics Data System (ADS)

    Bohler, Christopher Lee

    The energy and spin dependence of dissociating collisions between two types of noble gas metastable atoms and cadmium dihalide molecules have been studied in a flowing afterglow apparatus. The fluorescence spectra obtained in the range of 3000-7600 A which result from the Ar( ^{3}P_2) + CdX_2 interactions indicate a dominant dissociative excitation production mechanism. On the other hand, for the He(2^3S _1) + CdX_2 collisions, there appears to be competition between dissociative excitation and other "dark" channels. The emission spectra are further used to narrow the uncertainty in the currently accepted values for the dissociation energy of the CdX _2 molecules. The Wigner spin rule (conservation of total electronic spin) was verified for these processes as shown by the dominance of final state triplet production as compared to the virtual absence of singlet spin state production. In an attempt to further study the spin dependence of the dissociative excitation process, transfer of the longitudinal component of the electronic spin from oriented He(2 ^3S_1) atoms to Cd(6 ^3S_1) atoms was monitored. These data showed a null result for the transfor of the spin component, but were limited by a 3% systematic error of the apparatus. The spin dependent measurements rely on the ability to spin-polarize the He(2^3S _1) atoms by laser optical pumping methods. Four laser materials which exhibit promising characteristics for this procedure have been studied, and the results are presented for Nd^{3+}:YAP, La_{rm 1-x}Nd _{rm x}MgAl_ {11}O_{19}, Nd^{3+}:LiNbO _3, and Nd^{3+} :Silicate fibers.

  19. The First Swift Ultraviolet/Optical Telescope GRB Afterglow Catalog

    NASA Astrophysics Data System (ADS)

    Roming, P. W. A.; Koch, T. S.; Oates, S. R.; Porterfield, B. L.; Vanden Berk, D. E.; Boyd, P. T.; Holland, S. T.; Hoversten, E. A.; Immler, S.; Marshall, F. E.; Page, M. J.; Racusin, J. L.; Schneider, D. P.; Breeveld, A. A.; Brown, P. J.; Chester, M. M.; Cucchiara, A.; DePasquale, M.; Gronwall, C.; Hunsberger, S. D.; Kuin, N. P. M.; Landsman, W. B.; Schady, P.; Still, M.

    2009-01-01

    We present the first Swift Ultraviolet/Optical Telescope (UVOT) gamma-ray burst (GRB) afterglow catalog. The catalog contains data from over 64,000 independent UVOT image observations of 229 GRBs first detected by Swift, the High Energy Transient Explorer 2 (HETE2), the International Gamma-Ray Astrophysics Laboratory (INTEGRAL), and the Interplanetary Network (IPN). The catalog covers GRBs occurring during the period from 2005 January 17 to 2007 June 16 and includes ~86% of the bursts detected by the Swift Burst Alert Telescope (BAT). The catalog provides detailed burst positional, temporal, and photometric information extracted from each of the UVOT images. Positions for bursts detected at the 3σ level are provided with a nominal accuracy, relative to the USNO-B1 catalog, of ~0farcs25. Photometry for each burst is given in three UV bands, three optical bands, and a "white" or open filter. Upper limits for magnitudes are reported for sources detected below 3σ. General properties of the burst sample and light curves, including the filter-dependent temporal slopes, are also provided. The majority of the UVOT light curves, for bursts detected at the 3σ level, can be fit by a single power-law, with a median temporal slope (α) of 0.96, beginning several hundred seconds after the burst trigger and ending at ~1 × 105 s. The median UVOT v-band (~5500 Å) magnitude at 2000 s for a sample of "well"-detected bursts is 18.02. The UVOT flux interpolated to 2000 s after the burst, shows relatively strong correlations with both the prompt Swift BAT fluence, and the Swift X-ray flux at 11 hr after the trigger.

  20. GRB Orphan Afterglows in Present and Future Radio Transient Surveys

    NASA Astrophysics Data System (ADS)

    Ghirlanda, G.; Burlon, D.; Ghisellini, G.; Salvaterra, R.; Bernardini, M. G.; Campana, S.; Covino, S.; D'Avanzo, P.; D'Elia, V.; Melandri, A.; Murphy, T.; Nava, L.; Vergani, S. D.; Tagliaferri, G.

    2014-05-01

    Orphan Afterglows (OA) are slow transients produced by Gamma Ray Bursts seen off-axis that become visible on timescales of days/years at optical/NIR and radio frequencies, when the prompt emission at high energies (X and γ rays) has already ceased. Given the typically estimated jet opening angle of GRBs θjet ~ 3°, for each burst pointing to the Earth there should be a factor ~ 700 more GRBs pointing in other directions. Despite this, no secure OAs have been detected so far. Through a population synthesis code we study the emission properties of the population of OA at radio frequencies. OAs reach their emission peak on year-timescales and they last for a comparable amount of time. The typical peak fluxes (which depend on the observing frequency) are of few μJy in the radio band with only a few OA reaching the mJy level. These values are consistent with the upper limits on the radio flux of SN Ib/c observed at late times. We find that the OA radio number count distribution has a typical slope - 1.7 at high fluxes and a flatter ( - 0.4) slope at low fluxes with a break at a frequency-dependent flux. Our predictions of the OA rates are consistent with the (upper) limits of recent radio surveys and archive searches for radio transients. Future radio surveys like VAST/ASKAP at 1.4 GHz should detect ~ 3 × 10- 3 OA deg- 2 yr- 1, MeerKAT and EVLA at 8.4 GHz should see ~ 3 × 10- 1 OA deg- 2 yr- 1. The SKA, reaching the μJy flux limit, could see up to ~ 0.2 - 1.5 OA deg- 2 yr- 1. These rates also depend on the duration of the OA above a certain flux limit and we discuss this effect with respect to the survey cadence.

  1. The γ-ray afterglows of tidal disruption events

    NASA Astrophysics Data System (ADS)

    Chen, Xian; Gómez-Vargas, Germán Arturo; Guillochon, James

    2016-05-01

    A star wandering too close to a supermassive black hole (SMBH) will be tidally disrupted. Previous studies of such `tidal disruption event' (TDE) mostly focus on the stellar debris that are bound to the system, because they give rise to luminous flares. On the other hand, half of the stellar debris in principle are unbound and can stream to a great distance, but so far there is no clear evidence that this `unbound debris stream' (UDS) exists. Motivated by the fact that the circum-nuclear region around SMBHs is usually filled with dense molecular clouds (MCs), here we investigate the observational signatures resulting from the collision between an UDS and an MC, which is likely to happen hundreds of years after a TDE. We focus on γ-ray emission (0.1-105 GeV), which comes from the encounter of shock-accelerated cosmic rays with background protons and, more importantly, is not subject to extinction. We show that because of the high proton density inside an MC, the peak γ-ray luminosity, about 1039 erg s-1, is at least 100 times greater than that in the case without an MC (only with a smooth interstellar medium). The luminosity decays on a time-scale of decades, depending on the distance of the MC, and about a dozen of these `TDE afterglows' could be detected within a distance of about 16 Mpc by the future Cherenkov Telescope Array. Without careful discrimination, these sources potentially could contaminate the searches for starburst galaxies, galactic nuclei containing millisecond pulsars or dark matter annihilation signals.

  2. Fast Radio Bursts and Their Gamma-Ray or Radio Afterglows as Kerr-Newman Black Hole Binaries

    NASA Astrophysics Data System (ADS)

    Liu, Tong; Romero, Gustavo E.; Liu, Mo-Lin; Li, Ang

    2016-07-01

    Fast radio bursts (FRBs) are radio transients lasting only about a few milliseconds. They seem to occur at cosmological distances. We propose that these events can originate in the collapse of the magnetospheres of Kerr-Newman black holes (KNBHs). We show that the closed orbits of charged particles in the magnetospheres of these objects are unstable. After examining the dependencies on the specific charge of the particle and the spin and charge of the KNBH, we conclude that the resulting timescale and radiation mechanism fit well with extant observations of FRBs. Furthermore, we argue that the merger of a KNBH binary is a plausible central engine for the potential gamma-ray or radio afterglow following certain FRBs and can also account for gravitational wave (GW) events like GW 150914. Our model leads to predictions that can be tested by combined multi-wavelength electromagnetic and GW observations.

  3. SYNCHROTRON SELF-COMPTON EMISSION AS THE ORIGIN OF THE GAMMA-RAY AFTERGLOW OBSERVED IN GRB 980923

    SciTech Connect

    Fraija, N.; Gonzalez, M. M.; Lee, W. H. E-mail: magda@astro.unam.mx

    2012-05-20

    GRB 980923 was one of the brightest bursts observed by the Burst and Transient Source Experiment. Previous studies have detected two distinct components in addition to the main prompt episode, which is well described by a Band function. The first of these is a tail with a duration of {approx_equal} 400 s, while the second is a high-energy component lasting {approx_equal} 2 s. We summarize the observations and argue for a unified model in which the tail can be understood as the early {gamma}-ray afterglow from forward shock synchrotron emission, while the high-energy component arises from synchrotron self-Compton from the reverse shock. Consistency between the main assumption of thick shell emission and agreement between the observed and computed values for fluxes, break energies, starting times, and spectral indices leads to a requirement that the ejecta must be highly magnetized.

  4. Fast Radio Bursts and Their Gamma-Ray or Radio Afterglows as Kerr–Newman Black Hole Binaries

    NASA Astrophysics Data System (ADS)

    Liu, Tong; Romero, Gustavo E.; Liu, Mo-Lin; Li, Ang

    2016-07-01

    Fast radio bursts (FRBs) are radio transients lasting only about a few milliseconds. They seem to occur at cosmological distances. We propose that these events can originate in the collapse of the magnetospheres of Kerr–Newman black holes (KNBHs). We show that the closed orbits of charged particles in the magnetospheres of these objects are unstable. After examining the dependencies on the specific charge of the particle and the spin and charge of the KNBH, we conclude that the resulting timescale and radiation mechanism fit well with extant observations of FRBs. Furthermore, we argue that the merger of a KNBH binary is a plausible central engine for the potential gamma-ray or radio afterglow following certain FRBs and can also account for gravitational wave (GW) events like GW 150914. Our model leads to predictions that can be tested by combined multi-wavelength electromagnetic and GW observations.

  5. Bright x-ray flares in gamma-ray burst afterglows.

    PubMed

    Burrows, D N; Romano, P; Falcone, A; Kobayashi, S; Zhang, B; Moretti, A; O'brien, P T; Goad, M R; Campana, S; Page, K L; Angelini, L; Barthelmy, S; Beardmore, A P; Capalbi, M; Chincarini, G; Cummings, J; Cusumano, G; Fox, D; Giommi, P; Hill, J E; Kennea, J A; Krimm, H; Mangano, V; Marshall, F; Mészáros, P; Morris, D C; Nousek, J A; Osborne, J P; Pagani, C; Perri, M; Tagliaferri, G; Wells, A A; Woosley, S; Gehrels, N

    2005-09-16

    Gamma-ray burst (GRB) afterglows have provided important clues to the nature of these massive explosive events, providing direct information on the nearby environment and indirect information on the central engine that powers the burst. We report the discovery of two bright x-ray flares in GRB afterglows, including a giant flare comparable in total energy to the burst itself, each peaking minutes after the burst. These strong, rapid x-ray flares imply that the central engines of the bursts have long periods of activity, with strong internal shocks continuing for hundreds of seconds after the gamma-ray emission has ended.

  6. Model-Based Safety Analysis

    NASA Technical Reports Server (NTRS)

    Joshi, Anjali; Heimdahl, Mats P. E.; Miller, Steven P.; Whalen, Mike W.

    2006-01-01

    System safety analysis techniques are well established and are used extensively during the design of safety-critical systems. Despite this, most of the techniques are highly subjective and dependent on the skill of the practitioner. Since these analyses are usually based on an informal system model, it is unlikely that they will be complete, consistent, and error free. In fact, the lack of precise models of the system architecture and its failure modes often forces the safety analysts to devote much of their effort to gathering architectural details about the system behavior from several sources and embedding this information in the safety artifacts such as the fault trees. This report describes Model-Based Safety Analysis, an approach in which the system and safety engineers share a common system model created using a model-based development process. By extending the system model with a fault model as well as relevant portions of the physical system to be controlled, automated support can be provided for much of the safety analysis. We believe that by using a common model for both system and safety engineering and automating parts of the safety analysis, we can both reduce the cost and improve the quality of the safety analysis. Here we present our vision of model-based safety analysis and discuss the advantages and challenges in making this approach practical.

  7. Study of GRB Light-curve Decay Indices in the Afterglow Phase

    NASA Astrophysics Data System (ADS)

    Del Vecchio, Roberta; Dainotti, Maria Giovanna; Ostrowski, Michał

    2016-09-01

    In this work, we study the distribution of temporal power-law decay indices, α, in the gamma-ray burst (GRB) afterglow phase, fitted for 176 GRBs (139 long GRBs, 12 short GRBs with extended emission, and 25 X-ray flashes) with known redshifts. These indices are compared with the temporal decay index, α W , derived with the light-curve fitting using the Willingale et al. model. This model fitting yields similar distributions of α W to the fitted α, but for individual bursts a difference can be significant. Analysis of (α, L a ) distribution, where L a is the characteristic luminosity at the end of the plateau, reveals only a weak correlation of these quantities. However, we discovered a significant regular trend when studying GRB α values along the Dainotti et al. correlation between L a and the end time of the plateau emission in the rest frame, {T}a* , hereafter LT correlation. We note a systematic variation of the α parameter distribution with luminosity for any selected {T}a* . We analyze this systematics with respect to the fitted LT correlation line, expecting that the presented trend may allow us to constrain the GRB physical models. We also attempted to use the derived correlation of α ({T}a) versus {L}a({T}a) to diminish the luminosity scatter related to the variations of α along the LT distribution, a step forward in the effort of standardizing GRBs. A proposed toy model accounting for this systematics applied to the analyzed GRB distribution results in a slight increase of the LT correlation coefficient.

  8. Constraint Based Modeling Going Multicellular

    PubMed Central

    Martins Conde, Patricia do Rosario; Sauter, Thomas; Pfau, Thomas

    2016-01-01

    Constraint based modeling has seen applications in many microorganisms. For example, there are now established methods to determine potential genetic modifications and external interventions to increase the efficiency of microbial strains in chemical production pipelines. In addition, multiple models of multicellular organisms have been created including plants and humans. While initially the focus here was on modeling individual cell types of the multicellular organism, this focus recently started to switch. Models of microbial communities, as well as multi-tissue models of higher organisms have been constructed. These models thereby can include different parts of a plant, like root, stem, or different tissue types in the same organ. Such models can elucidate details of the interplay between symbiotic organisms, as well as the concerted efforts of multiple tissues and can be applied to analyse the effects of drugs or mutations on a more systemic level. In this review we give an overview of the recent development of multi-tissue models using constraint based techniques and the methods employed when investigating these models. We further highlight advances in combining constraint based models with dynamic and regulatory information and give an overview of these types of hybrid or multi-level approaches. PMID:26904548

  9. Constraint Based Modeling Going Multicellular.

    PubMed

    Martins Conde, Patricia do Rosario; Sauter, Thomas; Pfau, Thomas

    2016-01-01

    Constraint based modeling has seen applications in many microorganisms. For example, there are now established methods to determine potential genetic modifications and external interventions to increase the efficiency of microbial strains in chemical production pipelines. In addition, multiple models of multicellular organisms have been created including plants and humans. While initially the focus here was on modeling individual cell types of the multicellular organism, this focus recently started to switch. Models of microbial communities, as well as multi-tissue models of higher organisms have been constructed. These models thereby can include different parts of a plant, like root, stem, or different tissue types in the same organ. Such models can elucidate details of the interplay between symbiotic organisms, as well as the concerted efforts of multiple tissues and can be applied to analyse the effects of drugs or mutations on a more systemic level. In this review we give an overview of the recent development of multi-tissue models using constraint based techniques and the methods employed when investigating these models. We further highlight advances in combining constraint based models with dynamic and regulatory information and give an overview of these types of hybrid or multi-level approaches.

  10. Constraint Based Modeling Going Multicellular.

    PubMed

    Martins Conde, Patricia do Rosario; Sauter, Thomas; Pfau, Thomas

    2016-01-01

    Constraint based modeling has seen applications in many microorganisms. For example, there are now established methods to determine potential genetic modifications and external interventions to increase the efficiency of microbial strains in chemical production pipelines. In addition, multiple models of multicellular organisms have been created including plants and humans. While initially the focus here was on modeling individual cell types of the multicellular organism, this focus recently started to switch. Models of microbial communities, as well as multi-tissue models of higher organisms have been constructed. These models thereby can include different parts of a plant, like root, stem, or different tissue types in the same organ. Such models can elucidate details of the interplay between symbiotic organisms, as well as the concerted efforts of multiple tissues and can be applied to analyse the effects of drugs or mutations on a more systemic level. In this review we give an overview of the recent development of multi-tissue models using constraint based techniques and the methods employed when investigating these models. We further highlight advances in combining constraint based models with dynamic and regulatory information and give an overview of these types of hybrid or multi-level approaches. PMID:26904548

  11. Electron and ion acceleration in relativistic shocks with applications to GRB afterglows

    NASA Astrophysics Data System (ADS)

    Warren, Donald C.; Ellison, Donald C.; Bykov, Andrei M.; Lee, Shiu-Hang

    2015-09-01

    We have modelled the simultaneous first-order Fermi shock acceleration of protons, electrons, and helium nuclei by relativistic shocks. By parametrizing the particle diffusion, our steady-state Monte Carlo simulation allows us to follow particles from particle injection at non-relativistic thermal energies to above PeV energies, including the non-linear smoothing of the shock structure due to cosmic ray (CR) backpressure. We observe the mass-to-charge (A/Z) enhancement effect believed to occur in efficient Fermi acceleration in non-relativistic shocks and we parametrize the transfer of ion energy to electrons seen in particle-in-cell (PIC) simulations. For a given set of environmental and model parameters, the Monte Carlo simulation determines the absolute normalization of the particle distributions and the resulting synchrotron, inverse Compton, and pion-decay emission in a largely self-consistent manner. The simulation is flexible and can be readily used with a wide range of parameters typical of γ-ray burst (GRB) afterglows. We describe some preliminary results for photon emission from shocks of different Lorentz factors and outline how the Monte Carlo simulation can be generalized and coupled to hydrodynamic simulations of GRB blast waves. We assume Bohm diffusion for simplicity but emphasize that the non-linear effects we describe stem mainly from an extended shock precursor where higher energy particles diffuse further upstream. Quantitative differences will occur with different diffusion models, particularly for the maximum CR energy and photon emission, but these non-linear effects should be qualitatively similar as long as the scattering mean-free path is an increasing function of momentum.

  12. Model-based machine learning.

    PubMed

    Bishop, Christopher M

    2013-02-13

    Several decades of research in the field of machine learning have resulted in a multitude of different algorithms for solving a broad range of problems. To tackle a new application, a researcher typically tries to map their problem onto one of these existing methods, often influenced by their familiarity with specific algorithms and by the availability of corresponding software implementations. In this study, we describe an alternative methodology for applying machine learning, in which a bespoke solution is formulated for each new application. The solution is expressed through a compact modelling language, and the corresponding custom machine learning code is then generated automatically. This model-based approach offers several major advantages, including the opportunity to create highly tailored models for specific scenarios, as well as rapid prototyping and comparison of a range of alternative models. Furthermore, newcomers to the field of machine learning do not have to learn about the huge range of traditional methods, but instead can focus their attention on understanding a single modelling environment. In this study, we show how probabilistic graphical models, coupled with efficient inference algorithms, provide a very flexible foundation for model-based machine learning, and we outline a large-scale commercial application of this framework involving tens of millions of users. We also describe the concept of probabilistic programming as a powerful software environment for model-based machine learning, and we discuss a specific probabilistic programming language called Infer.NET, which has been widely used in practical applications. PMID:23277612

  13. Model-based machine learning.

    PubMed

    Bishop, Christopher M

    2013-02-13

    Several decades of research in the field of machine learning have resulted in a multitude of different algorithms for solving a broad range of problems. To tackle a new application, a researcher typically tries to map their problem onto one of these existing methods, often influenced by their familiarity with specific algorithms and by the availability of corresponding software implementations. In this study, we describe an alternative methodology for applying machine learning, in which a bespoke solution is formulated for each new application. The solution is expressed through a compact modelling language, and the corresponding custom machine learning code is then generated automatically. This model-based approach offers several major advantages, including the opportunity to create highly tailored models for specific scenarios, as well as rapid prototyping and comparison of a range of alternative models. Furthermore, newcomers to the field of machine learning do not have to learn about the huge range of traditional methods, but instead can focus their attention on understanding a single modelling environment. In this study, we show how probabilistic graphical models, coupled with efficient inference algorithms, provide a very flexible foundation for model-based machine learning, and we outline a large-scale commercial application of this framework involving tens of millions of users. We also describe the concept of probabilistic programming as a powerful software environment for model-based machine learning, and we discuss a specific probabilistic programming language called Infer.NET, which has been widely used in practical applications.

  14. Luminescence and afterglow in Sr{sub 2}SiO{sub 4}:Eu{sup 2+}, RE{sup 3+} [RE = Ce, Nd, Sm and Dy] phosphors-Role of co-dopants in search for afterglow

    SciTech Connect

    Lakshminarasimhan, N. Varadaraju, U.V.

    2008-11-03

    Luminescence of Eu{sup 2+} in Sr{sub 2}SiO{sub 4}:Eu{sup 2+}, RE{sup 3+} [RE = Ce, Nd, Sm and Dy] phosphors was studied with a view to obtain an afterglow phosphor. The synthesized phosphors were characterized by powder X-ray diffraction (XRD), diffuse reflectance, photo- and thermoluminescence spectroscopic techniques. Afterglow was observed only with Dy{sup 3+} co-doped phosphor. The observed afterglow with Dy{sup 3+} co-doping originated from the formation of suitable traps which was supported by thermoluminescence results.

  15. Kinetic simulations of argon dusty plasma afterglow including metastable atom kinetics

    SciTech Connect

    Alexandrov, A. L. Schweigert, I. V.; Ariskin, D. A.

    2013-04-15

    The afterglow of a dusty plasma of rf discharge in argon is simulated by the particle-in-cell-Monte Carlo collision (PIC-MCC) method. The experimental observation that heavy dust contamination of plasma leads to an anomalous increase in the electron density at the beginning of afterglow is explained by release of electrons from the dust surface. Under the assumption that the floating potential of particles is in equilibrium with plasma conditions, the fast cooling of electrons in afterglow plasma due to a rapid escape of hot electrons from the volume leads to a decrease in the magnitude of the floating potential and hence to a loss of charge by dust. The intensive desorption of electrons from nanoparticles is the origin of anomalous behavior of the electron density. At the next stage of afterglow, when the electrons become cool, the plasma decay is defined by ambipolar diffusion. The effect of metastable argon atoms is also considered. Additional ionization due to metastable atom collisions affects the electron temperature but does not change the behavior of the electron density qualitatively.

  16. Polarization Evolution of Early Optical Afterglows of Gamma-Ray Bursts

    NASA Astrophysics Data System (ADS)

    Lan, Mi-Xiang; Wu, Xue-Feng; Dai, Zi-Gao

    2016-01-01

    The central engine and jet composition of gamma-ray bursts (GRBs) remain mysterious. Here we suggest that observations on the polarization evolution of early optical afterglows may shed light on these questions. We first study the dynamics of a reverse shock and a forward shock that are generated during the interaction of a relativistic jet and its ambient medium. The jet is likely magnetized with a globally large-scale magnetic field from the central engine. The existence of the reverse shock requires that the magnetization degree of the jet should not be high (σ ≤ 1), so that the jet is mainly composed of baryons and leptons. We then calculate the light curves and polarization evolution of early optical afterglows and find that when the polarization position angle changes by 90° during the early afterglow, the polarization degree is zero for a toroidal magnetic field but is very likely to be nonzero for an aligned magnetic field. This result would be expected to provide a probe for the central engine of GRBs because an aligned field configuration could originate from a magnetar central engine and a toroidal field configuration could be produced from a black hole via the Blandford-Znajek mechanism. Finally, for such two kinds of magnetic field configurations, we fit the observed data of the early optical afterglow of GRB 120308A equally well.

  17. BRIGHT BROADBAND AFTERGLOWS OF GRAVITATIONAL WAVE BURSTS FROM MERGERS OF BINARY NEUTRON STARS

    SciTech Connect

    Gao He; Ding Xuan; Wu Xuefeng; Zhang Bing; Dai Zigao E-mail: zhang@physics.unlv.edu

    2013-07-10

    If double neutron star mergers leave behind a massive magnetar rather than a black hole, then a bright early afterglow can follow the gravitational wave burst (GWB) even if there is no short gamma-ray burst (SGRB)-GWB association or if there is an association but the SGRB does not beam toward Earth. Besides directly dissipating the proto-magnetar wind, as suggested by Zhang, here we suggest that the magnetar wind could push the ejecta launched during the merger process and, under certain conditions, would reach a relativistic speed. Such a magnetar-powered ejecta, when interacting with the ambient medium, would develop a bright broadband afterglow due to synchrotron radiation. We study this physical scenario in detail and present the predicted X-ray, optical, and radio light curves for a range of magnetar and ejecta parameters. We show that the X-ray and optical light curves usually peak around the magnetar spin-down timescale ({approx}10{sup 3}-10{sup 5} s), reaching brightnesses readily detectable by wide-field X-ray and optical telescopes, and remain detectable for an extended period. The radio afterglow peaks later, but is much brighter than the case without a magnetar energy injection. Therefore, such bright broadband afterglows, if detected and combined with GWBs in the future, would be a probe of massive millisecond magnetars and stiff equations of state for nuclear matter.

  18. Orphan Gamma-Ray Burst Radio Afterglows: Candidates and Constraints on Beaming

    NASA Astrophysics Data System (ADS)

    Levinson, Amir; Ofek, Eran O.; Waxman, Eli; Gal-Yam, Avishay

    2002-09-01

    The number of orphan radio afterglows associated with gamma-ray bursts (GRBs) that should be detected by a flux-limited radio survey is calculated. It is shown that for jetted GRBs, this number is smaller for a smaller jet opening angle θ, contrary to naive expectation. For a beaming factor f-1b≡(θ2/2)- 1~=500, roughly the value inferred by Frail et al. from analysis of afterglow light curves, we predict that between several hundred to several thousand orphan radio afterglows should be detectable (over all sky) above 1 mJy at GHz frequencies at any given time. This orphan population is dominated by sources lying at distances of a few hundred Mpc and having an age of ~1 yr. A search for pointlike radio transients with flux densities greater than 6 mJy was conducted using the FIRST and NVSS surveys, yielding a list of nine orphan candidates. We argue that most of the candidates are unlikely to be radio supernovae. However, the possibility that they are radio-loud active galactic nuclei cannot be ruled out without further observation. Our analysis sets a conservative 95% CL upper limit for the all-sky number of radio orphans, which corresponds to a lower limit f-1b>13 on the beaming factor. Rejection of all candidates found in our search would imply f-1b>80. This, and the possibility that some candidates may indeed be radio afterglows, strongly motivate further observations of these transients.

  19. GRB 080503 LATE AFTERGLOW RE-BRIGHTENING: SIGNATURE OF A MAGNETAR-POWERED MERGER-NOVA

    SciTech Connect

    Gao, He; Ding, Xuan; Wu, Xue-Feng; Dai, Zi-Gao; Zhang, Bing E-mail: xfwu@pmo.ac.cn E-mail: zhang@physics.unlv.edu

    2015-07-10

    GRB 080503 is a short gamma-ray burst (GRB) detected by Swift and has been classified as a GRB originating from a compact star merger. The soft extended emission and the simultaneous late re-brightening in both the X-ray and optical afterglow light curves raise interesting questions regarding its physical origin. We show that the broadband data of GRB 080503 can be well explained within the framework of the double neutron star merger model, provided that the merger remnant is a rapidly rotating massive neutron star with an extremely high magnetic field (i.e., a millisecond magnetar). We show that the late optical re-brightening is consistent with the emission from a magnetar-powered “merger-nova.” This adds one more case to the growing sample of merger-novae associated with short GRBs. The soft extended emission and the late X-ray excess emission are well connected through a magnetar dipole spin-down luminosity evolution function, suggesting that direct magnetic dissipation is the mechanism to produce these X-rays. The X-ray emission initially leaks from a hole in the merger ejecta pierced by the short GRB jet. The hole subsequently closes after the magnetar spins down and the magnetic pressure drops below ram pressure. The X-ray photons are then trapped behind the merger-nova ejecta until the ejecta becomes optically thin at a later time. This explains the essentially simultaneous re-brightening in both the optical and X-ray light curves. Within this model, future gravitational-wave sources could be associated with a bright X-ray counterpart along with the merger-nova, even if the short GRB jet beams away from Earth.

  20. Sketch-based geologic modeling

    NASA Astrophysics Data System (ADS)

    Rood, M. P.; Jackson, M.; Hampson, G.; Brazil, E. V.; de Carvalho, F.; Coda, C.; Sousa, M. C.; Zhang, Z.; Geiger, S.

    2015-12-01

    Two-dimensional (2D) maps and cross-sections, and 3D conceptual models, are fundamental tools for understanding, communicating and modeling geology. Yet geologists lack dedicated and intuitive tools that allow rapid creation of such figures and models. Standard drawing packages produce only 2D figures that are not suitable for quantitative analysis. Geologic modeling packages can produce 3D models and are widely used in the groundwater and petroleum communities, but are often slow and non-intuitive to use, requiring the creation of a grid early in the modeling workflow and the use of geostatistical methods to populate the grid blocks with geologic information. We present an alternative approach to rapidly create figures and models using sketch-based interface and modelling (SBIM). We leverage methods widely adopted in other industries to prototype complex geometries and designs. The SBIM tool contains built-in geologic rules that constrain how sketched lines and surfaces interact. These rules are based on the logic of superposition and cross-cutting relationships that follow from rock-forming processes, including deposition, deformation, intrusion and modification by diagenesis or metamorphism. The approach allows rapid creation of multiple, geologically realistic, figures and models in 2D and 3D using a simple, intuitive interface. The user can sketch in plan- or cross-section view. Geologic rules are used to extrapolate sketched lines in real time to create 3D surfaces. Quantitative analysis can be carried our directly on the models. Alternatively, they can be output as simple figures or imported directly into other modeling tools. The software runs on a tablet PC and can be used in a variety of settings including the office, classroom and field. The speed and ease of use of SBIM enables multiple interpretations to be developed from limited data, uncertainty to be readily appraised, and figures and models to be rapidly updated to incorporate new data or concepts.

  1. Measuring the beaming angle of GRB 030329 by fitting the rebrightenings in its multiband afterglow

    NASA Astrophysics Data System (ADS)

    Deng, Wei; Huang, Yong-Feng; Kong, Si-Wei

    2010-11-01

    Multiple rebrightenings have been observed in the multiband afterglow of GRB 030329. In particular, a marked and quick rebrightening occurred at about t ~ 1.2 × 105 s. Energy injection from late and slow shells seems to be the best interpretation for these rebrightenings. Usually it is assumed that the energy is injected into the whole external shock. However, in the case of GRB 030329, the rebrightenings are so quick that the usual consideration fails to give a satisfactory fit to the observed light curves. Actually, since these late/slow shells freely coast in the wake of the external shock, they should be cold and may not expand laterally. The energy injection then should only occur at the central region of the external shock. Considering this effect, we numerically re-fit the quick rebrightenings observed in GRB 030329. By doing this, we were able to derive the beaming angle of the energy injection process. Our result, with a relative residual of only 5% - 10% during the major rebrightening, is better than any previous modeling. The derived energy injection angle is about 0.035. We assume that these late shells are ejected by the central engine via the same mechanism as those early shells that produce the prompt gamma-ray burst. The main difference is that their velocities are much slower, so that they catch up with the external shock relatively late and are manifested as the observed quick rebrightenings. If this were true, then the derived energy injection angle can give a good measure of the beaming angle of the prompt γ-ray emission. Our study may hopefully provide a novel method to measure the beaming angle of gamma-ray bursts.

  2. Gamma-ray Burst Afterglows as Probes of Environment and Blastwave Physics: Absorption by Host Galaxy Gas and Dust, Circumburst Media and the Distribution of P

    NASA Technical Reports Server (NTRS)

    Starling, R. L. C.; Wijers, R. a. M. J.; Curran, P.; Rol, E.; Wiersema, K.; Kouveliotou, C.; vanderHorst, A. J.

    2006-01-01

    We use a new approach to obtain limits on the absorbing columns towards a sample of 10 Gamma-ray Bursts observed by BeppoSAX from simultaneous fits to X-ray, optical and IR data, in counts space and including the effects of metallicity. For half the afterglows the best-fitting model to the SED includes SMC-like extinction (as opposed to LMC or MW) and in one LMC-like extinction, and in no cases is there a preference for MW-like extinction. Gas-to-dust ratios generally do not match those of the 3 standard and most well-known extinction models of SMC, LMC and MW, but tend to be higher. We compare the results from this method to those of previous works using other methods. We constrain the jet models for a subsample of the bursts by constraining the cooling break position and power law spectral slopes, allowing the injected electron energy index to be measured. We derive secure values of p from our spectral fits and comparison with the temporal optical and X-ray slopes for 4 afterglows. The mean of these single value, suggesting that either external factors such as circumburst medium play a strong role or that the microphysics is not identical for each GRB. For GRB 971214 we find that the circumburst medium has a wind-like density profile and the cooling frequency appears to be moving to higher frequencies.

  3. An investigation into the role of metastable argon atoms in the afterglow plasma of a low pressure discharge

    NASA Astrophysics Data System (ADS)

    Strauss, J. A.; Ferreira, N. P.; Human, H. G. C.

    An investigation into the behaviour of metastable argon atoms in a low pressure (250 Pa) pulsed electrical discharge was undertaken in an effort to find the cause of the persisting emission from sputtered metal atoms in the afterglow of an atomic fluorimeter. Results obtained by time-resolved emission and absorption measurements of several argon and copper spectral lines indicate that low energy electrons in the afterglow are converted to high energy electrons via the recombination of electrons with argon ions and the subsequent collisions of pairs of metastable argon atoms. The high energy electrons excite the sputtered metal atoms to give rise to a slow decaying emission tail in the afterglow. A probable change in the electron energy distribution in the afterglow may also have an effect on the observed emission. This phenomenon may be reduced by the use of a suitable quenching gas.

  4. The puzzling afterglow of GRB 050721: a rebrightening seen in the optical but not in the X-ray

    SciTech Connect

    Antonelli, L. A.; Romano, P.; Testa, V.; D'Elia, V.; Guetta, D.; Torii, K.; Malesani, D.

    2007-08-21

    We present here the analysis of the early and late multiwavelength afterglow emission, as observed by Swift a small robotic telescope, and the VLT. We compare early observations with late afterglow observations obtained with Swift and the VLT and we observe an intense rebrightening in the optical band at about one day after the burst which is not present in the X-ray band. The lack of detection in X-ray of such a strong rebrightening at lower energies may be described with a variable external density profile. In such a scenario, the combined X-ray and optical observations allow us to derive that the matter density located at {approx} 1017 cm from the burst is about a factor of 10 higher than in the inner region. This is the first time in which a rebrightening has been observed in the optical afterglow of a GRB that is clearly absent in the X-ray afterglow.

  5. Optical light curve of GRB 121011A: a textbook for the onset of GRB afterglow in a mixture of ISM and wind-type medium

    NASA Astrophysics Data System (ADS)

    Xin, Li-Ping; Wei, Jian-Yan; Qiu, Yu-Lei; Deng, Jin-Song; Wang, Jing; Han, Xu-Hui

    2016-01-01

    We report the optical observations of GRB 121011A by the 0.8m TNT facility at Xinglong observatory, China. The light curve of the optical afterglow shows a smooth and featureless bump during the epoch of ∼130 s and ∼5000 s with a rising index of 1.57 ± 0.28 before the break time of 539 ± 44 s, and a decaying index of about 1.29 ± 0.07 up to the end of our observations. Moreover, the X-ray light curve decays in a single power-law with a slope of about 1.51 ± 0.03 observed by XRT onboard Swift from 100 s to about 10 000 s after the burst trigger. The featureless optical light curve could be understood as an onset process under the external-shock model. The typical frequency has been below or near the optical one before the deceleration time, and the cooling frequency is located between the optical and X-ray wavelengths. The external medium density has a transition from a mixed stage of ISM and wind-type medium before the peak time to the ISM at the later phase. The joint-analysis of X-ray and optical light curves shows that the emissions from both frequencies are consistent with the prediction of the standard afterglow model without any energy injections, indicating that the central engine has stopped its activity and does not restart anymore after the prompt phase.

  6. The potential for detecting gamma-ray burst afterglows from population III stars with the next generation of infrared telescopes

    SciTech Connect

    Macpherson, D.; Coward, D. M.; Zadnik, M. G.

    2013-12-10

    We investigate the detectability of a proposed population of gamma-ray bursts (GRBs) from the collapse of Population III (Pop III) stars. The James Webb Space Telescope (JWST) and Space Infrared Telescope for Cosmology and Astrophysics (SPICA) will be able to observe the late time infrared afterglows. We have developed a new method to calculate their detectability, which takes into account the fundamental initial mass function and formation rates of Pop III stars, from which we find the temporal variability of the afterglows and ultimately the length of time JWST and SPICA can detect them. In the range of plausible Pop III GRB parameters, the afterglows are always detectable by these instruments during the isotropic emission, for a minimum of 55 days and a maximum of 3.7 yr. The average number of detectable afterglows will be 2.96× 10{sup –5} per SPICA field of view (FOV) and 2.78× 10{sup –6} per JWST FOV. These are lower limits, using a pessimistic estimate of Pop III star formation. An optimal observing strategy with SPICA could identify a candidate orphan afterglow in ∼1.3 yr, with a 90% probability of confirmation with further detailed observations. A beamed GRB will align with the FOV of the planned GRB detector Energetic X-ray Imaging Survey Telescope once every 9 yr. Pop III GRBs will be more easily detected by their isotropic emissions (i.e., orphan afterglows) rather than by their prompt emissions.

  7. The Potential for Detecting Gamma-Ray Burst Afterglows from Population III Stars with the Next Generation of Infrared Telescopes

    NASA Astrophysics Data System (ADS)

    Macpherson, D.; Coward, D. M.; Zadnik, M. G.

    2013-12-01

    We investigate the detectability of a proposed population of gamma-ray bursts (GRBs) from the collapse of Population III (Pop III) stars. The James Webb Space Telescope (JWST) and Space Infrared Telescope for Cosmology and Astrophysics (SPICA) will be able to observe the late time infrared afterglows. We have developed a new method to calculate their detectability, which takes into account the fundamental initial mass function and formation rates of Pop III stars, from which we find the temporal variability of the afterglows and ultimately the length of time JWST and SPICA can detect them. In the range of plausible Pop III GRB parameters, the afterglows are always detectable by these instruments during the isotropic emission, for a minimum of 55 days and a maximum of 3.7 yr. The average number of detectable afterglows will be 2.96× 10-5 per SPICA field of view (FOV) and 2.78× 10-6 per JWST FOV. These are lower limits, using a pessimistic estimate of Pop III star formation. An optimal observing strategy with SPICA could identify a candidate orphan afterglow in ~1.3 yr, with a 90% probability of confirmation with further detailed observations. A beamed GRB will align with the FOV of the planned GRB detector Energetic X-ray Imaging Survey Telescope once every 9 yr. Pop III GRBs will be more easily detected by their isotropic emissions (i.e., orphan afterglows) rather than by their prompt emissions.

  8. Model-based tomographic reconstruction

    DOEpatents

    Chambers, David H.; Lehman, Sean K.; Goodman, Dennis M.

    2012-06-26

    A model-based approach to estimating wall positions for a building is developed and tested using simulated data. It borrows two techniques from geophysical inversion problems, layer stripping and stacking, and combines them with a model-based estimation algorithm that minimizes the mean-square error between the predicted signal and the data. The technique is designed to process multiple looks from an ultra wideband radar array. The processed signal is time-gated and each section processed to detect the presence of a wall and estimate its position, thickness, and material parameters. The floor plan of a building is determined by moving the array around the outside of the building. In this paper we describe how the stacking and layer stripping algorithms are combined and show the results from a simple numerical example of three parallel walls.

  9. Energy based hybrid turbulence modeling

    NASA Astrophysics Data System (ADS)

    Haering, Sigfried; Moser, Robert

    2015-11-01

    Traditional hybrid approaches exhibit deficiencies when used for fluctuating smooth-wall separation and reattachment necessitating ad-hoc delaying functions and model tuning making them no longer useful as a predictive tool. Additionally, complex geometries and flows often require high cell aspect-ratios and large grid gradients as a compromise between resolution and cost. Such transitions and inconsistencies in resolution detrimentally effect the fidelity of the simulation. We present the continued development of a new hybrid RANS/LES modeling approach specifically developed to address these challenges. In general, modeled turbulence is returned to resolved scales by reduced or negative model viscosity until a balance between theoretical and actual modeled turbulent kinetic energy is attained provided the available resolution. Anisotropy in the grid and resolved field are directly integrated into this balance. A viscosity-based correction is proposed to account for resolution inhomogeneities. Both the hybrid framework and resolution gradient corrections are energy conserving through an exchange of resolved and modeled turbulence.

  10. GRB 050826: A Subluminous Event at z=0.296 Finds Its Place in the Luminosity Distribution of Gamma-Ray Burst Afterglows

    NASA Technical Reports Server (NTRS)

    Mirabal, N.; Halpern J. P.; O'Brien, P. T.

    2007-01-01

    We present the optical identification and spectroscopy of the host galaxy of GRB 050826 at redshift z = 0.296 +/- 0.001. Image subtraction among observations obtained on three consecutive nights reveals a fading object 5 hr after the burst, confirming its identification as the optical afterglow of this event. Deep imaging shows that the optical afterglow is offset by 0.4" (1.76 kpc) from the center of its irregular host galaxy, which is typical for long-duration gamma-ray bursts. Combining these results with X-ray measurements acquired by the Swift XRT instrument, we find that GRB 050826 falls entirely within the subluminous, subenergetic group of long gamma-ray bursts at low redshift (z less than or equal to 0.3). The results are discussed in the context of models that possibly account for this trend, including the nature of the central engine, the evolution of progenitor properties as a function of redshift, and incompleteness in current gamma-ray burst samples.

  11. Erosion of a-C:H films under interaction with nitrous oxide afterglow discharge

    NASA Astrophysics Data System (ADS)

    Zalavutdinov, R. Kh.; Gorodetsky, A. E.; Bukhovets, V. L.; Zakharov, A. P.; Mazul, I. V.

    2009-06-01

    Hydrocarbon film removal using chemically active oxygen formed in a direct current glow discharge with a hollow cathode in nitrous oxide was investigated. In the afterglow region sufficiently fast removal of a-C:H films about 500 nm thick during about 8 h was achieved at N 2O pressure of 12 Pa and 370 K. The erosion rate in the afterglow region was directly proportional to the initial pressure and increased two orders of magnitude at temperature rising from 300 to 500 K. The products of a-C:H film plasmolysis were CO, CO 2, H 2O, and H 2. After removal of a-C:H films previously deposited on stainless steel, molybdenum or tungsten 3-30 nm thick oxide films were formed on the substrates. Reactions of oxygen ion neutralization and atomic oxygen recombination suppressed further oxidation of the materials.

  12. Long afterglow properties of Zn2GeO4:Mn2+, Cr3+ phosphor

    NASA Astrophysics Data System (ADS)

    Cong, Yan; He, Yangyang; Dong, Bin; Xiao, Yu; Wang, Limei

    2015-04-01

    Zn2GeO4:Mn2+, Cr3+ phosphors were prepared by conventional solid state reaction and the photoluminescence properties were investigated. The Mn2+ activated Zn2GeO4 phosphors exhibited green emission at 533 nm due to the 4T1(4G) → 6A1(6S) transition of Mn2+ ions. With Cr3+ co-doping in Zn2GeO4 host, long afterglow characteristics were found from the same transition of Mn2+. The TL results revealed the presence of same traps in the phosphor, and the doping of Cr3+ ions deepened the VGe traps. The native defect VGe as a hole traps is responsible for the long afterglow emission in Zn2GeO4:Mn2+, Cr3+ phosphor. The possible mechanism of this phosphor has also been discussed.

  13. The effectiveness of strong afterglow phosphor powder in the detection of fingermarks.

    PubMed

    Liu, Li; Zhang, Zhongliang; Zhang, Limei; Zhai, Yuchun

    2009-01-10

    There are numerous types of fluorescent fingermark powders or reagents used with the visualization of latent fingermarks deposited on multicolored substrate surfaces that can present a contrast problem if developed with regular fingermark powders. The developed fingermarks can show bright fluorescence upon exposure to laser, ultraviolet light and other light sources. These kinds of methods share a common concern, where surfaces and other substrates may fluoresce also. To overcome this concern, we have developed a phosphor powder which offers a strong afterglow effect which aid in the establishment of better fingermark detection. With the advent of a phosphor powder no special devices are required and the results obtained from fresh or a few days aged latent fingermarks left on: non-porous; semi-porous and also on some porous surfaces have been good. The strong afterglow effect offered by phosphor powder is also applicable for cyanoacrylate fumed fingermarks. Lift off and photography procedures of the developed fingermarks are incorporated in this paper.

  14. A Search for Early High-Energy Afterglows in BATSE Gamma-Ray Bursts

    NASA Technical Reports Server (NTRS)

    Giblin, Timothy W.

    2003-01-01

    The scope of this project was to perform a detailed search for the early high-energy afterglow component of gamma-ray bursts (GRBs) in the BATSE GRB data archive. GRBs are believed to be the product of shock waves generated in a relativistic outflow from the demise of extremely massive stars and/or binary neutron star mergers. The outflow undeniably encounters the ambient medium of the progenitor object and another shock wave is set up. A forward shock propagates into the medium and a reverse shock propagates through the ejecta. This "external" shock dissipates the kinetic energy of the ejecta in the form of radiation via synchrotron losses and slows the outflow eventually to a non-relativistic state. Radiation from the forward external shock is therefore expected to be long-lived, lasting days, weeks, and even months. This radiation is referred to as the 'afterglow'.

  15. X-RAY AFTERGLOW OF SWIFT J1644+57: A COMPTON ECHO?

    SciTech Connect

    Cheng, K. S.; Chernyshov, D. O.; Dogiel, V. A.; Kong, Albert K. H.; Ko, C. M.

    2016-01-01

    Swift, Chandra, and XMM have found a weak but nearly constant X-ray component from Swift J1644+57 that appeared at ∼500 days and was visible at least until ∼1400 days after the stellar capture, which cannot be explained by standard tidal disruption theories. We suggest that this X-ray afterglow component may result from the Thomson scattering between the primary X-rays and its surrounding plasma, i.e., a Compton echo effect. Similar phenomena have also been observed from molecular clouds in our Galactic Center, which were caused by the past activity of Srg A*. If this interpretation of Swift J1644+57 afterglow is correct, this is the first Compton Echo effect observed in the cosmological distances.

  16. Characterization of a Plasmoid in the Afterglow of a Supersonic Flowing Microwave Discharge

    NASA Technical Reports Server (NTRS)

    Drake, D. J.; Miller, S.; Nikolic, M.; Popovic, S.; Vuskovic, L.

    2009-01-01

    We performed a detailed characterization a plasmoid in the afterglow region of an Ar supersonic microwave cavity discharge. The supersonic flow was generated using a convergent-divergent nozzle upstream of the discharge region. A cylindrical cavity was used to sustain a discharge in the pressure range of 100-600 Pa. Optical emission spectroscopy was used to observe populations of excited and ionic species in the plasmoid region. Plasmoid formation in the supersonic flowing afterglow located downstream from the primary microwave cavity discharge was characterized by measuring the radial and axial distributions of Argon excited states and Argon ions. More experiments are being carried out on the plasmoid to understand the discharge parameters within the region, i.e. rotational temperature, vibrational temperature, electron density, and how the electrodynamic and aerodynamic effects combine to form this plasmoid.

  17. Strategies for Prompt Searches for GRB Afterglows: The Discovery of GRB 001011 Optical/Near-Infrared Counterpart Using Colour-Colour Selection

    NASA Technical Reports Server (NTRS)

    Gorosabel, J.; Fynbo, J. U.; Hjorth, J.; Wolf, C.; Andersen, M. I.; Pedersen, H.; Christensen, L.; Jensen, B. L.; Moller, P.; Afonso, J.; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    We report the discovery of the optical and near-infrared counterpart to GRB 001011. The GRB 001011 error box determined by Beppo-SAX was simultaneously imaged in the near-infrared by the 3.58-m. New Technology Telescope and in the optical by the 1.54-m Danish Telescope - 8 hr after the gamma-ray event. We implement the colour-colour discrimination technique proposed by Rhoads (2001) and extend it using near-IR data as well. We present the results provided by an automatic colour-colour discrimination pipe-line developed to discern the different populations of objects present in the GRB 001011 error box. Our software revealed three candidates based on single-epoch images. Second-epoch observations carried out approx. 3.2 days after the burst revealed that the most likely candidate had faded thus identifying it with the counterpart to the GRB. In deep R-band images obtained 7 months after the burst a faint (R=25.38 plus or minus 0.25) elongated object, presumably the host galaxy of GRB 001011, was detected at the position of the afterglow. The GRB 001011 afterglow is the first discovered with the assistance of colour-colour diagram techniques. We discuss the advantages of using this method and its application to boxes determined by future missions.

  18. Hydrothermal synthesis and afterglow luminescence properties of hollow SnO{sub 2}:Sm{sup 3+},Zr{sup 4+} spheres for potential application in drug delivery

    SciTech Connect

    Feng, Pengfei; Zhang, Jiachi Qin, Qingsong; Hu, Rui; Wang, Yuhua

    2014-02-01

    Highlights: • We designed a novel afterglow labeling material SnO{sub 2}:Sm{sup 3+},Zr{sup 4+} for the first time. • Hollow SnO{sub 2}:Sm{sup 3+},Zr{sup 4+} spheres with afterglow were prepared by hydrothermal method. • Hollow SnO{sub 2}:Sm{sup 3+},Zr{sup 4+} is a potential afterglow labeling medium for drug delivery. - Abstract: A novel afterglow labeling material SnO{sub 2}:Sm{sup 3+},Zr{sup 4+} with hollow sphere shape and intense afterglow luminescence is prepared by hydrothermal method at 180 °C for the first time. The morphology and the sphere growth process of this material are investigated by scanning electron microscopy in detail. The afterglow measurement shows that this hydrothermal obtained material exhibits obvious red afterglow luminescence (550–700 nm) of Sm{sup 3+} which can last for 542 s (0.32 mcd/m{sup 2}). The depth of traps in this hydrothermal obtained material is calculated to be as shallow as 0.58 eV. The results demonstrate that although it is necessary to further improve the afterglow performance of the hydrothermal derived hollow SnO{sub 2}:Sm{sup 3+},Zr{sup 4+} spheres, it still can be regarded as a potential afterglow labeling medium for drug delivery.

  19. Crowdsourcing Based 3d Modeling

    NASA Astrophysics Data System (ADS)

    Somogyi, A.; Barsi, A.; Molnar, B.; Lovas, T.

    2016-06-01

    Web-based photo albums that support organizing and viewing the users' images are widely used. These services provide a convenient solution for storing, editing and sharing images. In many cases, the users attach geotags to the images in order to enable using them e.g. in location based applications on social networks. Our paper discusses a procedure that collects open access images from a site frequently visited by tourists. Geotagged pictures showing the image of a sight or tourist attraction are selected and processed in photogrammetric processing software that produces the 3D model of the captured object. For the particular investigation we selected three attractions in Budapest. To assess the geometrical accuracy, we used laser scanner and DSLR as well as smart phone photography to derive reference values to enable verifying the spatial model obtained from the web-album images. The investigation shows how detailed and accurate models could be derived applying photogrammetric processing software, simply by using images of the community, without visiting the site.

  20. Observation of antibacterial effects obtained at atmospheric and reduced pressures in afterglow conditions

    NASA Astrophysics Data System (ADS)

    Sarrette, J.-P.; Cousty, S.; Merbahi, N.; Nègre-Salvayre, A.; Clément, F.

    2010-01-01

    Bactericidal activities of three different afterglows operating at reduced and atmospheric pressures and ambient temperature are established and compared through the use of a unique protocol for bacteria (E. coli, CIP 54.8 T) exposition, recovery and numeration. The influence of three important parameters is shown. An original scenario for bacterial inactivation at reduced pressure is proposed, compatible with previously published results and with the observation of conformational changes appearing on the treated bacteria.

  1. A global study of X-Ray afterglows of GRBs after the plateau

    NASA Astrophysics Data System (ADS)

    Bardho, Onelda; Boer, Michel; Gendre, Bruce

    We have investigated the behavior and correlations in X-ray light curves of GRB afterglows following the earlier results from Boer and Gendre (2000) and Gendre and Boer (2008). We have used data from 160 GRBs observed by Swift, corrected from distance effects. We have applied several statistical tests on this extended data. We discuss the correlations present in the sample and the possible origin of them.

  2. Shock-wave-induced enhancement of optical emission in nitrogen afterglow plasma

    SciTech Connect

    Siefert, N.; Ganguly, B.N.; Bletzinger, P.

    2005-12-15

    This paper reports measurements of optical emission enhancement at the shock front of Mach 1.5 to Mach 3.5 shockwaves propagating in the afterglow of a 0.75 Torr nitrogen glow discharge. Electrically-generated shocks pass through the afterglow and create noticeable enhancements of the B {sup 3}{pi}{sub g}-A {sup 3}{sigma}{sub u}{sup +} and C {sup 3}{pi}{sub u}-B {sup 3}{pi}{sub g} transitions of nitrogen. Under our discharge conditions, the electron Debye length was approximately the same magnitude as the shock thickness; this allows the possibility of a space-charge region extending beyond the neutral shockwave discontinuity. Previous researchers have measured enhancement in the B {sup 3}{pi}{sub g}-A {sup 3}{sigma}{sub u}{sup +} optical emission at the shock front, but only in the active discharge. Fibers connected to photomultipler tubes measure the optical emission from the discharge. Laser deflection measures the shock velocity. The data reveals that the emission enhancement increases with Mach number, and also indicates that the emission enhancement decreases exponentially with time in the afterglow. Since the discharge voltage has already been shut off, the energy needed to create the emission enhancement cannot come from the power supply. We conclude that under our discharge conditions there is an increase in the already non-equilibrium energy of the electrons at the shock front via a shockwave-induced strong double layer.

  3. Shock-wave-induced enhancement of optical emission in nitrogen afterglow plasma.

    PubMed

    Siefert, N; Ganguly, B N; Bletzinger, P

    2005-12-01

    This paper reports measurements of optical emission enhancement at the shock front of Mach 1.5 to Mach 3.5 shockwaves propagating in the afterglow of a 0.75 Torr nitrogen glow discharge. Electrically-generated shocks pass through the afterglow and create noticeable enhancements of the B 3Pig-A 3Sigma+u and C 3Piu-B 3Pig transitions of nitrogen. Under our discharge conditions, the electron Debye length was approximately the same magnitude as the shock thickness; this allows the possibility of a space-charge region extending beyond the neutral shockwave discontinuity. Previous researchers have measured enhancement in the B 3Pig-A 3Sigma+u optical emission at the shock front, but only in the active discharge. Fibers connected to photomultipler tubes measure the optical emission from the discharge. Laser deflection measures the shock velocity. The data reveals that the emission enhancement increases with Mach number, and also indicates that the emission enhancement decreases exponentially with time in the afterglow. Since the discharge voltage has already been shut off, the energy needed to create the emission enhancement cannot come from the power supply. We conclude that under our discharge conditions there is an increase in the already non-equilibrium energy of the electrons at the shock front via a shockwave-induced strong double layer.

  4. Estimates for Lorentz factors of gamma-ray bursts from early optical afterglow observations

    SciTech Connect

    Hascoët, Romain; Beloborodov, Andrei M.; Daigne, Frédéric; Mochkovitch, Robert

    2014-02-10

    The peak time of optical afterglow may be used as a proxy to constrain the Lorentz factor Γ of the gamma-ray burst (GRB) ejecta. We revisit this method by including bursts with optical observations that started when the afterglow flux was already decaying; these bursts can provide useful lower limits on Γ. Combining all analyzed bursts in our sample, we find that the previously reported correlation between Γ and the burst luminosity L {sub γ} does not hold. However, the data clearly show a lower bound Γ{sub min} that increases with L {sub γ}. We suggest an explanation for this feature: explosions with large jet luminosities and Γ < Γ{sub min} suffer strong adiabatic cooling before their radiation is released at the photosphere; they produce weak bursts, barely detectable with present instruments. To test this explanation, we examine the effect of adiabatic cooling on the GRB location in the L {sub γ} – Γ plane using a Monte Carlo simulation of the GRB population. Our results predict detectable on-axis 'orphan' afterglows. We also derive upper limits on the density of the ambient medium that decelerates the explosion ejecta. We find that the density in many cases is smaller than expected for stellar winds from normal Wolf-Rayet progenitors. The burst progenitors may be peculiar massive stars with weaker winds, or there might exist a mechanism that reduces the stellar wind a few years before the explosion.

  5. Kinematics of Gamma-Ray Burst and their Relationship to Afterglows

    SciTech Connect

    Salmonson, J D

    2001-12-17

    A strong correlation is reported between gamma-ray burst (GRB) pulse lags and afterglow jet-break times for the set of bursts (seven) with known redshifts, luminosities, pulse lags, and jet-break times. This may be a valuable clue toward understanding the connection between the burst and afterglow phases of these events. The relation is roughly linear (i.e. doubling the pulse lag in turn doubles the jet break time) and thus implies a simple relationship between these quantities. We suggest that this correlation is due to variation among bursts of emitter Doppler factor. Specifically, an increased speed or decreased angle of velocity, with respect to the observed line-of-site, of burst ejecta will result in shorter perceived pulse lags in GRBs as well as quicker evolution of the external shock of the afterglow to the time when the jet becomes obvious, i.e. the jet-break time. Thus this observed variation among GRBs may result from a perspective effect due to different observer angles of a morphologically homogeneous populations of GRBs. Also, a conjecture is made that peak luminosities not only vary inversely with burst timescale, but also are directly proportional to the spectral break energy. If true, this could provide important information for explaining the source of this break.

  6. GAMMA-RAY BURST AFTERGLOW SCALING RELATIONS FOR THE FULL BLAST WAVE EVOLUTION

    SciTech Connect

    Van Eerten, Hendrik J.; MacFadyen, Andrew I.

    2012-03-10

    We demonstrate that gamma-ray burst afterglow spectra and light curves can be calculated for arbitrary explosion and radiation parameters by scaling the peak flux and the critical frequencies connecting different spectral regimes. Only one baseline calculation needs to be done for each jet opening angle and observer angle. These calculations are done numerically using high-resolution relativistic hydrodynamical afterglow blast wave simulations which include the two-dimensional dynamical features of expanding and decelerating afterglow blast waves. Any light curve can then be generated by applying scaling relations to the baseline calculations. As a result, it is now possible to fully fit for the shape of the jet break, e.g., at early-time X-ray and optical frequencies. In addition, late-time radio calorimetry can be improved since the general shape of the transition into the Sedov-Taylor regime is now known for arbitrary explosion parameters so the exact moment when the Sedov-Taylor asymptote is reached in the light curve is no longer relevant. When calculating the baselines, we find that the synchrotron critical frequency {nu}{sub m} and the cooling break frequency {nu}{sub c} are strongly affected by the jet break. The {nu}{sub m} temporal slope quickly drops to the steep late-time Sedov-Taylor slope, while the cooling break {nu}{sub c} first steepens and then rises to meet the level of its shallow late-time asymptote.

  7. Optical flashes from internal pairs formed in gamma-ray burst afterglows

    DOE PAGES

    Panaitescu, A.

    2015-06-09

    We develop a numerical formalism for calculating the distribution with energy of the (internal) pairs formed in a relativistic source from unscattered MeV–TeV photons. For gamma-ray burst (GRB) afterglows, this formalism is more suitable if the relativistic reverse shock that energizes the ejecta is the source of the GeV photons. The number of pairs formed is set by the source GeV output (calculated from the Fermi-LAT fluence), the unknown source Lorentz factor, and the unmeasured peak energy of the LAT spectral component. We show synchrotron and inverse-Compton light curves expected from pairs formed in the shocked medium and identify some criteria for testing a pair origin of GRB optical counterparts. Pairs formed in bright LAT afterglows with a Lorentz factor in the few hundreds may produce bright optical counterparts (more » $$R\\lt 10$$) lasting for up to one hundred seconds. As a result, the number of internal pairs formed from unscattered seed photons decreases very strongly with the source Lorentz factor, thus bright GRB optical counterparts cannot arise from internal pairs if the afterglow Lorentz factor is above several hundreds.« less

  8. Luminescence of divalent europium activated spinels synthesized by combustion and the enhanced afterglow by dysprosium incorporation

    NASA Astrophysics Data System (ADS)

    Wu, Haoyi; Jin, Yahong

    2016-05-01

    Herein we report a luminescent phenomenon of Eu2+ in the spinel MgAl2O4 and ZnAl2O4 samples which are successfully synthesized via a combustion method. The XRD shows cubic spinel structure is obtained from the prepared samples. The mean crystal sizes estimated from XRD data are 30 and 10 nm for MgAl2O4 and ZnAl2O4 respectively, and the large grain particles are the agglomeration of crystallites. The Eu2+ ions show a blue emission at around 480 nm and an afterglow phenomenon is observed after the removal of excitation. The afterglow spectrum of MgAl2O4: Eu2+, Dy3+ shows two emissions at 480 and 520 nm while only one at 480 nm is observed in ZnAl2O4: Eu2+, Dy3+. The afterglow intensity and the persisting duration can be substantially enhanced by the Dy3+ incorporation because the trapping ability of the electron traps is reinforced. This is confirmed by the TL curves of the samples.

  9. Evidence for a Canonical GRB Afterglow Light Curve in the Swift/XRT Data

    NASA Technical Reports Server (NTRS)

    Nousek, J. A.; Kouveliotou, C.; Grupe, D.; Page, K.; Granot, J.; Ramirez-Ruiz, E.; Patel, S. K.; Burrows, D. N.; Mangano, V.; Barthelmy, S.

    2005-01-01

    We present new observations of the early X-ray afterglows of the first 27 gamma-ray bursts (GRBs) detected with the Swift X-ray Telescope (XRT). The early X-ray afterglows show a canonical behavior, where the light curve broadly consists of three distinct power law segments. These power law segments are separated by two corresponding break times. On top of this canonical behavior of the early X-ray light curve, many events have superimposed X-ray flares, which are most likely caused by internal shocks due to long lasting sporadx activity of the central engine, up to several hours after the GRB. We find that the initial steep decay is consistent with it being the tail of the prompt emission: from photons that are radiated at large angles relative to our line of sight. The first break in the light curve takes place when the forward shock emission becomes dominant, with the intermediate shallow flux decay likely caused by the continuous energy injection into the external shock. When this energy injection stops, a second break is then observed in the light curve. This energy injection increases the energy of the afterglow shock by at least a factor of f greater than or approx. equal to 4, and augments the already severe requirements for the efficiency of the prompt gamma-ray emission.

  10. Afterglow Population Studies from Swift Follow-Up Observations of Fermi LAT GRBs

    NASA Technical Reports Server (NTRS)

    Racusin, Judith L.; Oates, S. R.; McEnery, J.; Vasileiou, V.; Troja, E.; Gehrels, N.

    2010-01-01

    The small population of Fermi LAT detected GRBs discovered over the last year has been providing interesting and unexpected clues into GRB prompt and afterglow emission mechanisms. Over the last 5 years, it has been Swift that has provided the robust data set of UV/optical and X-ray afterglow observations that opened many windows into other components of GRB emission structure. We explore the new ability to utilize both of these observatories to study the same GRBs over 10 orders of magnitude in energy, although not always concurrently. Almost all LAT GRBs that have been followed-up by Swift within 1-day have been clearly detected and carefully observed. We will present the context of the lower-energy afterglows of this special subset of GRBs that has > 100 MeV emission compared to the hundreds in the Swift database that may or may not have been observed by LAT, and theorize upon the relationship between these properties and the origin of the high energy gamma-ray emission.

  11. Discovery of the Low-Redshift Afterglow of GRB 011121 and Its Progenitor Supernova 2001ke

    NASA Astrophysics Data System (ADS)

    Garnavich, P. M.; Stanek, K. Z.; Wyrzykowski, L.; Infante, L.; Bendek, E.; Holland, S. T.; Bersier, D.; Jha, S.; Matheson, T.; Kirshner, R. P.; Phillips, M. M.; Krisciunas, K.; Carlberg, R.

    2002-05-01

    We identify and present the first optical observations of the afterglow of the Gamma-Ray Burst (GRB) 011121. Images were obtained with the OGLE 1.3m telescope in BVRI passbands, starting 10.3;hours after the burst. The temporal analysis of our data indicates a steep decay, independent of wavelength with Fν t{-1.72+/- 0.05}. There is no evidence for a break in the light curve earlier than 2.5 days after the burst. The spectral energy distribution determined from the early broad-band photometry is a power-law with Fν ν {-0.46+/- 0.10} after correcting for a large Galactic extinction. Spectra, obtained with the Magellan 6.5m Baade telescope, reveal narrow emission lines from the host galaxy and these provide a redshift of z=0.36, which is the lowest measured redshift for an optical afterglow. We also present late R and J-band observations of the afterglow ~ 14;days after the burst. The late-time photometry shows a large deviation from the initial decline and our data combined with Hubble Space Telescope photometry provide strong evidence for a supernova peaking less than 10 rest-frame days after the GRB. This is the best evidence to date that classical, long gamma-ray bursts are generated by core-collapse supernovae. This work is partially supported by NASA LTSA grant NAG5-9364.

  12. Crystal Composition and Afterglow in Mixed Silicates: The Role of Melting Temperature

    NASA Astrophysics Data System (ADS)

    Sidletskiy, O.; Vedda, A.; Fasoli, M.; Neicheva, S.; Gektin, A.

    2015-08-01

    Modern applications of scintillator materials demand cutting-edge performances and require often a response speed in the nanosecond time scale. Slow light emission causing an "afterglow" is, therefore, of considerable concern in the development of fast scintillators. The mechanism of afterglow emission in mixed Ce-doped oxyorthosilicate scintillators is investigated by means of time-resolved scintillation, thermally stimulated luminescence (TSL), and radio-luminescence measurements. Various Ce-doped Lu2 xGd2 -2 xSiO5 oxyorthosilicate crystals (with x ranging from 0 to1) and Lu1.8Y0.2SiO5 grown by the Czochralski technique are considered. The detailed TSL analysis reveals that thermally assisted tunneling recombination of electrons trapped by oxygen vacancies with holes trapped by Ce luminescence centers occurs for all compositions. The reduction of the afterglow intensity by adding gadolinium or yttrium into the host is accompanied by a lowering of the traps concentration, as deduced by the TSL intensity. Such lowering of the oxygen vacancy concentrations is found to be correlated with the decrease of the melting temperature induced by gadolinium or yttrium content increase, which governs the oxygen vapor pressure. The occurrence of a similar mechanism also in other scintillators and its influence on carrier trapping is discussed.

  13. The afterglow of XRF 071031: Evidence for correlated optical and X-ray flares

    SciTech Connect

    Kruehler, T.; Greiner, J.; Clemens, C.; McBreen, S.; Klose, S.; Rossi, A.; Yoldas, A. Kuepcue

    2009-05-25

    We present a densely sampled early light curve of the optical/near-infrared (NIR) afterglow of the X-Ray Flash (XRF) 071031 at z 2.692. Continuous observations in seven photometric bands from g' to K{sub S} simultaneously with the Gamma Ray Burst Optical Near-Infrared Detector (GROND) at the 2.2 m MPI/ESO telescope on LaSilla were performed between 4 minutes and 7 hours after the burst. The optical/NIR light curve is dominated by an early increase in brightness which can be attributed to the apparent onset of the forward shock (FS) emission. In addition, there are several bumps which are superimposed onto the overall rise and decay. Significant flaring is also visible in the Swift X-Ray Telescope (XRT) light curve at early and late times. The broadband data enables detailed studies of the connection between the X-ray and optical/NIR afterglow and its colour evolution during the first night post burst. We find evidence of spectral hardening in the optical spectral energy distribution contemporaneous with the emergence of the bumps from an underlying afterglow component. The bumps in the optical/NIR light curve can be associated with flares in the X-ray regime suggesting late central engine activity as the common origin.

  14. CORRELATED OPTICAL AND X-RAY FLARES IN THE AFTERGLOW OF XRF 071031

    SciTech Connect

    Kruehler, T.; Greiner, J.; McBreen, S.; Afonso, P.; Clemens, C.; Filgas, R.; Yoldas, A.; Klose, S.; Rossi, A.; Yoldas, A. Kuepcue; Szokoly, G. P.

    2009-05-20

    We present a densely sampled early light curve of the optical/near-infrared (NIR) afterglow of the X-Ray Flash (XRF) 071031 at z = 2.692. Simultaneous and continuous observations in seven photometric bands from g' to K{sub S} with GROND (Gamma-Ray Burst Optical/Near-InfraRed Detector) at the 2.2-m MPI/ESO telescope on LaSilla were performed between 4 minutes and 7 hr after the burst. The light curve consists of 547 individual points which allows us to study the early evolution of the optical transient associated with XRF 071031 in great detail. The optical/NIR light curve is dominated by an early increase in brightness which can be attributed to the apparent onset of the forward shock emission. There are several bumps which are superimposed onto the overall rise and decay. Significant flaring is also visible in the Swift X-Ray Telescope (XRT) light curve from early to late times. The availability of high-quality, broadband data enables detailed studies of the connection between the X-ray and optical/NIR afterglow and its color evolution during the first night postburst. We find evidence of spectral hardening in the optical bands contemporaneous with the emergence of the bumps from an underlying afterglow component. The bumps in the optical/NIR light curve can be associated with flares in the X-ray regime suggesting late central engine activity as the common origin.

  15. Estimates for Lorentz Factors of Gamma-Ray Bursts from Early Optical Afterglow Observations

    NASA Astrophysics Data System (ADS)

    Hascoët, Romain; Beloborodov, Andrei M.; Daigne, Frédéric; Mochkovitch, Robert

    2014-02-01

    The peak time of optical afterglow may be used as a proxy to constrain the Lorentz factor Γ of the gamma-ray burst (GRB) ejecta. We revisit this method by including bursts with optical observations that started when the afterglow flux was already decaying; these bursts can provide useful lower limits on Γ. Combining all analyzed bursts in our sample, we find that the previously reported correlation between Γ and the burst luminosity L γ does not hold. However, the data clearly show a lower bound Γmin that increases with L γ. We suggest an explanation for this feature: explosions with large jet luminosities and Γ < Γmin suffer strong adiabatic cooling before their radiation is released at the photosphere; they produce weak bursts, barely detectable with present instruments. To test this explanation, we examine the effect of adiabatic cooling on the GRB location in the L γ - Γ plane using a Monte Carlo simulation of the GRB population. Our results predict detectable on-axis "orphan" afterglows. We also derive upper limits on the density of the ambient medium that decelerates the explosion ejecta. We find that the density in many cases is smaller than expected for stellar winds from normal Wolf-Rayet progenitors. The burst progenitors may be peculiar massive stars with weaker winds, or there might exist a mechanism that reduces the stellar wind a few years before the explosion.

  16. Optical flashes from internal pairs formed in gamma-ray burst afterglows

    SciTech Connect

    Panaitescu, A.

    2015-06-09

    We develop a numerical formalism for calculating the distribution with energy of the (internal) pairs formed in a relativistic source from unscattered MeV–TeV photons. For gamma-ray burst (GRB) afterglows, this formalism is more suitable if the relativistic reverse shock that energizes the ejecta is the source of the GeV photons. The number of pairs formed is set by the source GeV output (calculated from the Fermi-LAT fluence), the unknown source Lorentz factor, and the unmeasured peak energy of the LAT spectral component. We show synchrotron and inverse-Compton light curves expected from pairs formed in the shocked medium and identify some criteria for testing a pair origin of GRB optical counterparts. Pairs formed in bright LAT afterglows with a Lorentz factor in the few hundreds may produce bright optical counterparts ($R\\lt 10$) lasting for up to one hundred seconds. As a result, the number of internal pairs formed from unscattered seed photons decreases very strongly with the source Lorentz factor, thus bright GRB optical counterparts cannot arise from internal pairs if the afterglow Lorentz factor is above several hundreds.

  17. Unified GRB Paradigm: Correlation between Afterglow Beaming Fraction and Gamma-ray Spectral Lag

    NASA Astrophysics Data System (ADS)

    Norris, J. P.

    2001-12-01

    Without redshifts, studies of the pulse structures in gamma-ray bursts (GRBs) were largely phenomenological. Now that approximately twenty GRBs have associated redshifts, it is clear that cosmological GRBs exhibit a large dynamic range in observed luminosity and total energy. Thus from afterglow measurements, inferences on the physics of GRB spectral/temporal properties become possible. For a subset of bursts where redshifts and BATSE data are available, a correlation between luminosity and spectral lag has been reported (Norris, Marani & Bonnell 2001, ApJ 534, 248). It has also been demonstrated from breaks in GRB afterglow temporal decays (e.g., Frail et al. 2001, ApJL, accepted) that GRBs manifest a wide dynamic range in opening angle, or beaming fraction -- implying more uniform isotropic luminosities and energies for GRBs. Even more exciting, the beaming fraction and average spectral lag appear to be correlated (both being related to luminosity), signaling a profound, but indirect, link between the gamma-ray and afterglow phases. While the sample is still small, and the analysis techniques for beaming fraction and spectral lag are still being refined, it is possible to extend observed BATSE distributions and prognosticate on distributional properties of GRBs, such as luminosity and redshift, that should be observable by Swift.

  18. Model-based Utility Functions

    NASA Astrophysics Data System (ADS)

    Hibbard, Bill

    2012-05-01

    Orseau and Ring, as well as Dewey, have recently described problems, including self-delusion, with the behavior of agents using various definitions of utility functions. An agent's utility function is defined in terms of the agent's history of interactions with its environment. This paper argues, via two examples, that the behavior problems can be avoided by formulating the utility function in two steps: 1) inferring a model of the environment from interactions, and 2) computing utility as a function of the environment model. Basing a utility function on a model that the agent must learn implies that the utility function must initially be expressed in terms of specifications to be matched to structures in the learned model. These specifications constitute prior assumptions about the environment so this approach will not work with arbitrary environments. But the approach should work for agents designed by humans to act in the physical world. The paper also addresses the issue of self-modifying agents and shows that if provided with the possibility to modify their utility functions agents will not choose to do so, under some usual assumptions.

  19. Kinetics of excited states and radicals in a nanosecond pulse discharge and afterglow in nitrogen and air

    NASA Astrophysics Data System (ADS)

    Shkurenkov, Ivan; Burnette, David; Lempert, Walter R.; Adamovich, Igor V.

    2014-12-01

    The present kinetic modelling calculation results provide key new insights into the kinetics of vibrational excitation of nitrogen and plasma chemical reactions in nanosecond pulse, ‘diffuse filament’ discharges in nitrogen and dry air at a moderate energy loading per molecule, ˜0.1 eV per molecule. It is shown that it is very important to take into account Coulomb collisions between electrons because they change the electron energy distribution function and, as a result, strongly affect populations of excited states and radical concentrations in the discharge. The results demonstrate that the apparent transient rise of N2 ‘first level’ vibrational temperature after the discharge pulse, as detected in the experiments, is due to the net downward V-V energy transfer in N2-N2 collisions, which increases the N2(X 1Σ, v = 1) population. Finally, a comparison of the model's predictions with the experimental data shows that NO formation in the afterglow occurs via reactive quenching of multiple excited electronic levels of nitrogen molecule, N2\\ast , by O atoms. ) published in this volume, which focuses on the kinetic modelling of the experiments. This paper presents the results of the experiments.

  20. The low-extinction afterglow in the solar-metallicity host galaxy of γ-ray burst 110918A

    NASA Astrophysics Data System (ADS)

    Elliott, J.; Krühler, T.; Greiner, J.; Savaglio, S.; Olivares, F.; Rau, E. A.; de Ugarte Postigo, A.; Sánchez-Ramírez, R.; Wiersema, K.; Schady, P.; Kann, D. A.; Filgas, R.; Nardini, M.; Berger, E.; Fox, D.; Gorosabel, J.; Klose, S.; Levan, A.; Nicuesa Guelbenzu, A.; Rossi, A.; Schmidl, S.; Sudilovsky, V.; Tanvir, N. R.; Thöne, C. C.

    2013-08-01

    Galaxies selected through long γ-ray bursts (GRBs) could be of fundamental importance when mapping the star formation history out to the highest redshifts. Before using them as efficient tools in the early Universe, however, the environmental factors that govern the formation of GRBs need to be understood. Metallicity is theoretically thought to be a fundamental driver in GRB explosions and energetics, but it is still, even after more than a decade of extensive studies, not fully understood. This is largely related to two phenomena: a dust-extinction bias, which prevented high-mass and thus likely high-metallicity GRB hosts from being detected in the first place, and a lack of efficient instrumentation, which limited spectroscopic studies, including metallicity measurements, to the low-redshift end of the GRB host population. The subject of this work is the very energetic GRB 110918A (Eγ,iso = 1.9 × 1054 erg), for which we measure a redshift of z = 0.984. GRB 110918A gave rise to a luminous afterglow with an intrinsic spectral slope of β = 0.70, which probed a sight-line with little extinction (AGRBV = 0.16 mag) and soft X-ray absorption (NH,X = (1.6 ± 0.5) × 1021 cm-2) typical of the established distributions of afterglow properties. However, photometric and spectroscopic follow-up observations of the galaxy hosting GRB 110918A, including optical/near-infrared photometry with the Gamma-Ray burst Optical Near-infrared Detector and spectroscopy with the Very Large Telescope/X-shooter, reveal an all but average GRB host in comparison to the z ~ 1 galaxies selected through similar afterglows to date. It has a large spatial extent with a half-light radius of R1/2 ~ 10 kpc, the highest stellar mass for z < 1.9 (log (M∗/M⊙) = 10.68 ± 0.16), and an Hα-based star formation rate of SFRHα = 41+28-16M⊙ yr-1. We measure a gas-phase extinction of AgasV ~ 1.8 mag through the Balmer decrement and one of the largest host-integrated metallicities ever of around solar

  1. The Achromatic Light Curve of the Optical Afterglow of GRB 030226 at a Redshift of z Approximately 2

    NASA Technical Reports Server (NTRS)

    Klose, S.; Greiner, J.; Rau, A.; Henden, A. A.; Hartmann, D. H.; Zeh, A.; Masetti, N.; Guenther, E.; Stecklum, B.; Lindsay, K.

    2003-01-01

    Abstract. We report on optical and near-infrared (NIR) follow-up observations of the afterglow of GRB 030226, mainly performed with the telescopes at ESO La Silla and Paranal, with additional data obtained at other places. Our first observations started 0.2 days after the burst when the afterglow was at a magnitude of R approximately equal to 19 . One week later the magnitude of the afterglow had fallen to R=25, and at two weeks after the burst it could no longer be detected (R > 26). Our VLT blueband spectra show two absorption line systems at redshifts z = 1.962 +/- 0.001 and at z = 1.986 +/- 0.001, placing the redshift of the burster close to 2. Within our measurement errors no evidence for variations in the line strengths has been found between 0.2 and 1.2 days after the burst. An overabundance of alpha-group elements might indicate that the burst occurred in a chemically young interstellar region shaped by the nucleosynthesis from type II supernovae. The spectral slope of the afterglow shows no signs for cosmic dust along the line of sight in the GRB host galaxy, which itself remained undetected (R > 26.2). At the given redshift no supernova component affected the light from the GRB afterglow, so that the optical transient was essentially only powered by the radiation from the GRB fireball, allowing for a detailed investigation of the color evolution of the afterglow light. In our data set no obvious evidence for color changes has been found before, during, or after the smooth break in the light curve approximately 1 day after the burst. In comparison with investigations by others, our data favor the interpretation that the afterglow began to develop into a homogeneous interstellar medium before the break in the light curve became apparent.

  2. Chemical abundances associated with gamma-ray bursts: nucleosynthesis in afterglows

    NASA Astrophysics Data System (ADS)

    Hu, Tao; Wang, Min

    2014-03-01

    Gamma-ray burst (GRB) ejecta carries huge amounts of energy expanding into the surrounding medium and heats up these materials, making it possible that nucleosynthesis can take place in such hot sites in afterglow stage. Here, we study possible changes in chemical abundances in the GRB afterglow processes of Wolf-Rayet (WR) star wind environments (Case A) and constant density surroundings (Case B). We find that the light element of lithium-beryllium-boron could occur in the afterglows via He+He process and spallation reactions. Some isotopes of F, Ne, Mg, Al, Si, P, S and Fe-group elements are also new species formed in the afterglows via proton-, neutron- and α-capture. The results show that the nucleosynthetic yields might be a diagnostic of the GRB's ambient environment. Our calculations indicate that Mg, Al, Si, P, Cr, Mn, Fe and Co have trended to appear in Case A, while Ne, Ti and Ni trend to occur in Case B. Furthermore, although some species have occurred both in Cases A and B, their mass fractions are quite different in these two cases. Here, we show that the mass fractions of 7Li, 7Be, 24Mg and 30Si are higher in Case A than that in Case B, but 18F gives an opposite conclusion. Nucleosynthetic outputs might also be an indice to estimate the luminosity-temperature relation factor β. In this study, when β reduces, the mass abundances of 11B and 20Ne are higher in Case B than that in Case A; in contrast, as the β becomes larger, this trend would be reversed; therefore, perhaps we could select the above elements as the indicators to estimate the properties of the surroundings around the GRBs. We also suggest that the spectroscopic observations of a GRB afterglow could only reveal the nucleosynthetic outputs from the interaction site between the GRB jet and its ambient matter, but could not represent the original composition of the pre-GRB surrounding medium.

  3. Microwave afterglow studies of electron-ion recombination at low temperatures

    SciTech Connect

    Macdonald, J.A.

    1982-01-01

    A specially constructed low temperature microwave afterglow mass spectrometer apparatus employing microwave heating of the electrons has been used to study the dissociative recombination of the complex molecular ions Ne/sub 3//sup +/, H/sub 3//sup +/, and H/sub 5//sup +/ with electrons. The measured electron decays in recombination controlled afterglows are fitted by computer solutions of the continuity equation containing recombination and ambipolar diffusion loss terms. At approx. = 80K and approx. = 6 Torr of neon, Ne/sub 3//sup +/ is the dominant afterglow ion. The recombination coefficient, ..cap alpha..(Ne/sub 3//sup +/), has been determined over the range 80K less than or equal to T/sub e/ less than or equal to 4000K, and the result may be expressed as ..cap alpha..(Ne/sub 3//sup +/) = (1.1 +/- 0.1) x 10/sup -6/((T/sub e/)/(300))/sup -0/ /sup 36/cm/sup 3//sec with T/sub +/ = T/sub g/ = 80K. This trimer ion exhibits a dependence on electron temperature similar to that predicted and measured for diatomic ions but a larger (> 10/sup -6/cm/sup 3//sec) room temperature rate coefficient. Admixtures of approx. = 1 mTorr of H/sub 2/ in 20 Torr of neon at 265K lead to an H/sub 3//sup +/ dominated afterglow. The recombination coefficient, ..cap alpha..(H/sub 3//sup +/) varies little over the range 256 less than or equal to T/sub e/ < approx. = 400K, then approaches a T/sub e//sup (-0/88)/ variation, i.e., ..cap alpha..(H/sub 3//sup +/) = (2.0 +/- 0.3) x 10/sup -7/((T/sub e/)/(300))/sup -0/ /sup 88/ cm/sup 3//sec for approx. = 400K afterglow study. This T/sub e//sup -0/ /sup 88/ variation at higher temperatures than the T/sub e//sup (-0.5)/ to T/sub e//sup (-0.24) variations derived from e- + H/sub 3//sup +/ recombination

  4. MAGNETICALLY DRIVEN WINDS FROM DIFFERENTIALLY ROTATING NEUTRON STARS AND X-RAY AFTERGLOWS OF SHORT GAMMA-RAY BURSTS

    SciTech Connect

    Siegel, Daniel M.; Ciolfi, Riccardo; Rezzolla, Luciano

    2014-04-10

    Besides being among the most promising sources of gravitational waves, merging neutron star binaries also represent a leading scenario to explain the phenomenology of short gamma-ray bursts (SGRBs). Recent observations have revealed a large subclass of SGRBs with roughly constant luminosity in their X-ray afterglows, lasting 10-10{sup 4} s. These features are generally taken as evidence of a long-lived central engine powered by the magnetic spin-down of a uniformly rotating, magnetized object. We propose a different scenario in which the central engine powering the X-ray emission is a differentially rotating hypermassive neutron star (HMNS) that launches a quasi-isotropic and baryon-loaded wind driven by the magnetic field, which is built-up through differential rotation. Our model is supported by long-term, three-dimensional, general-relativistic, and ideal magnetohydrodynamic simulations, showing that this isotropic emission is a very robust feature. For a given HMNS, the presence of a collimated component depends sensitively on the initial magnetic field geometry, while the stationary electromagnetic luminosity depends only on the magnetic energy initially stored in the system. We show that our model is compatible with the observed timescales and luminosities and express the latter in terms of a simple scaling relation.

  5. DETERMINATION OF THE INTRINSIC LUMINOSITY TIME CORRELATION IN THE X-RAY AFTERGLOWS OF GAMMA-RAY BURSTS

    SciTech Connect

    Dainotti, Maria Giovanna; Petrosian, Vahe'; Singal, Jack; Ostrowski, Michal E-mail: vahep@stanford.edu E-mail: dainotti@oa.uj.edu.pl

    2013-09-10

    Gamma-ray bursts (GRBs), which have been observed up to redshifts z Almost-Equal-To 9.5, can be good probes of the early universe and have the potential to test cosmological models. Dainotti's analysis of GRB Swift afterglow light curves with known redshifts and a definite X-ray plateau shows an anti-correlation between the rest-frame time when the plateau ends (the plateau end time) and the calculated luminosity at that time (or approximately an anti-correlation between plateau duration and luminosity). Here, we present an update of this correlation with a larger data sample of 101 GRBs with good light curves. Since some of this correlation could result from the redshift dependences of these intrinsic parameters, namely, their cosmological evolution, we use the Efron-Petrosian method to reveal the intrinsic nature of this correlation. We find that a substantial part of the correlation is intrinsic and describe how we recover it and how this can be used to constrain physical models of the plateau emission, the origin of which is still unknown. The present result could help to clarify the debated nature of the plateau emission.

  6. Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph and FORS2 spectroscopy of the GRB 081008 afterglow

    NASA Astrophysics Data System (ADS)

    D'Elia, V.; Campana, S.; Covino, S.; D'Avanzo, P.; Piranomonte, S.; Tagliaferri, G.

    2011-11-01

    We aim at studying the gamma-ray burst (GRB), GRB 081008, environment by analysing the spectra of its optical afterglow. Ultraviolet and Visual Echelle Spectrograph/Very Large Telescope (UVES/VLT) high-resolution spectroscopy of GRB 081008 was secured ˜5 h after the Swift-BAT trigger. Our data set also comprises three VLT/FORS2 nearly simultaneous spectra of the same source. The availability of nearly simultaneous high- and low-resolution spectra for a GRB afterglow is an extremely rare event. The GRB-damped Lyman α system at z= 1.9683 shows that the interstellar medium (ISM) of the host galaxy is constituted by at least three components which contribute to the line profiles. Component I is the redmost one, and is 20 and 78 km s-1 redward components II and III, respectively. We detect several ground state and excited absorption features in components I and II. These features have been used to compute the distances between the GRB and the absorbers. Component I is found to be 52 ± 6 pc away from the GRB, while component II presents few excited transitions and its distance is 200+60- 80 pc. Component III only features a few, low-ionization and saturated lines suggesting that it is even farther from the GRB. Component I represents the closest absorber ever detected near a GRB. This (relatively) low distance can possibly be a consequence of a dense GRB environment, which prevents the GRB prompt/afterglow emission to strongly affect the ISM up to higher distances. The hydrogen column density associated with GRB 081008 is log NH/cm-2= 21.11 ± 0.10, and the metallicity of the host galaxy is in the range of [X/H] =-1.29 to -0.52. In particular, we found [Fe/H] =-1.19 ± 0.11 and [Zn/H] =-0.52 ± 0.11 with respect to solar values. This discrepancy can be explained by the presence of dust in the GRB ISM, given the opposite refractory properties of iron and zinc. By deriving the depletion pattern for GRB 081008, we find the optical extinction in the visual band to be AV

  7. Intelligent model-based OPC

    NASA Astrophysics Data System (ADS)

    Huang, W. C.; Lai, C. M.; Luo, B.; Tsai, C. K.; Chih, M. H.; Lai, C. W.; Kuo, C. C.; Liu, R. G.; Lin, H. T.

    2006-03-01

    Optical proximity correction is the technique of pre-distorting mask layouts so that the printed patterns are as close to the desired shapes as possible. For model-based optical proximity correction, a lithographic model to predict the edge position (contour) of patterns on the wafer after lithographic processing is needed. Generally, segmentation of edges is performed prior to the correction. Pattern edges are dissected into several small segments with corresponding target points. During the correction, the edges are moved back and forth from the initial drawn position, assisted by the lithographic model, to finally settle on the proper positions. When the correction converges, the intensity predicted by the model in every target points hits the model-specific threshold value. Several iterations are required to achieve the convergence and the computation time increases with the increase of the required iterations. An artificial neural network is an information-processing paradigm inspired by biological nervous systems, such as how the brain processes information. It is composed of a large number of highly interconnected processing elements (neurons) working in unison to solve specific problems. A neural network can be a powerful data-modeling tool that is able to capture and represent complex input/output relationships. The network can accurately predict the behavior of a system via the learning procedure. A radial basis function network, a variant of artificial neural network, is an efficient function approximator. In this paper, a radial basis function network was used to build a mapping from the segment characteristics to the edge shift from the drawn position. This network can provide a good initial guess for each segment that OPC has carried out. The good initial guess reduces the required iterations. Consequently, cycle time can be shortened effectively. The optimization of the radial basis function network for this system was practiced by genetic algorithm

  8. Sensor-based interior modeling

    SciTech Connect

    Herbert, M.; Hoffman, R.; Johnson, A.; Osborn, J.

    1995-02-01

    Robots and remote systems will play crucial roles in future decontamination and decommissioning (D&D) of nuclear facilities. Many of these facilities, such as uranium enrichment plants, weapons assembly plants, research and production reactors, and fuel recycling facilities, are dormant; there is also an increasing number of commercial reactors whose useful lifetime is nearly over. To reduce worker exposure to radiation, occupational and other hazards associated with D&D tasks, robots will execute much of the work agenda. Traditional teleoperated systems rely on human understanding (based on information gathered by remote viewing cameras) of the work environment to safely control the remote equipment. However, removing the operator from the work site substantially reduces his efficiency and effectiveness. To approach the productivity of a human worker, tasks will be performed telerobotically, in which many aspects of task execution are delegated to robot controllers and other software. This paper describes a system that semi-automatically builds a virtual world for remote D&D operations by constructing 3-D models of a robot`s work environment. Planar and quadric surface representations of objects typically found in nuclear facilities are generated from laser rangefinder data with a minimum of human interaction. The surface representations are then incorporated into a task space model that can be viewed and analyzed by the operator, accessed by motion planning and robot safeguarding algorithms, and ultimately used by the operator to instruct the robot at a level much higher than teleoperation.

  9. Synthesis of ZnS:Ag,Co water-soluble blue afterglow nanoparticles and application in photodynamic activation

    NASA Astrophysics Data System (ADS)

    Ma, Lun; Zou, Xiaoju; Hossu, Marius; Chen, Wei

    2016-08-01

    Silver and cobalt co-doped ZnS (ZnS:Ag,Co) water-soluble afterglow nanoparticles were synthesized using a wet chemistry method followed by aging at room temperature. The nanoparticles had a cubic zinc blende structure with average sizes of approximately 4 nm and emitted a blue fluorescence emission centered at 441 nm due to radiative transitions from surface defects to Ag+ luminescent centers. Intense afterglow emission peaking at 475 nm from the obtained nanoparticles was observed and was red-shifted compared to the fluorescence emission peak. X-ray photoelectron spectroscopy revealed a large increase of O/S ratio, indicating a surface oxidation process during aging. The S vacancies produced accordingly may contribute to form more electron traps and enhance afterglow. The ZnS:Ag,Co afterglow nanoparticles have a very low dark-toxicity and are applied as a light source for photodynamic therapy activation by conjugating with protoporphyrin together. Our preliminary study has shown that the ZnS:Ag,Co afterglow nanoparticles can significantly reduce the x-ray dosage used in activation and thus may be a very promising candidate for future x-ray excited photodynamic therapy in deep cancer treatment.

  10. Determination of state-to-state electron-impact rate coefficients between Ar excited states: a review of combined diagnostic experiments in afterglow plasmas

    NASA Astrophysics Data System (ADS)

    Zhu, Xi-Ming; Cheng, Zhi-Wen; Carbone, Emile; Pu, Yi-Kang; Czarnetzki, Uwe

    2016-08-01

    Electron-impact excitation processes play an important role in low-temperature plasma physics. Cross section and rate coefficient data for electron-impact processes from the ground state to excited states or between two excited states are required for both diagnostics and modeling works. However, the collisional processes between excited states are much less investigated than the ones involving the ground state due to various experimental challenges. Recently, a method for determining electron excitation rate coefficients between Ar excited states in afterglow plasmas was successfully implemented and further developed to obtain large sets of collisional data. This method combines diagnostics for electron temperature, electron density, and excited species densities and kinetic modeling of excited species, from which the electron excitation rate coefficients from one of the 1s states to the other 1s states or to one of 2p or 3p states are determined (states are in Paschen’s notation). This paper reviews the above method—namely the combined diagnostics and modeling in afterglow plasmas. The results from other important approaches, including electron-beam measurement of cross sections, laser pump-probe technique for measuring rate coefficients, and theoretical calculations by R-matrix and distorted-wave models are also discussed. From a comparative study of these results, a fitted mathematical expression of excitation rate coefficients is obtained for the electron temperature range of 1-5 eV, which can be used for the collisional-radiative modeling of low-temperature Ar plasmas. At last, we report the limitations in the present dataset and give some suggestions for future work in this area.

  11. Determination of state-to-state electron-impact rate coefficients between Ar excited states: a review of combined diagnostic experiments in afterglow plasmas

    NASA Astrophysics Data System (ADS)

    Zhu, Xi-Ming; Cheng, Zhi-Wen; Carbone, Emile; Pu, Yi-Kang; Czarnetzki, Uwe

    2016-08-01

    Electron-impact excitation processes play an important role in low-temperature plasma physics. Cross section and rate coefficient data for electron-impact processes from the ground state to excited states or between two excited states are required for both diagnostics and modeling works. However, the collisional processes between excited states are much less investigated than the ones involving the ground state due to various experimental challenges. Recently, a method for determining electron excitation rate coefficients between Ar excited states in afterglow plasmas was successfully implemented and further developed to obtain large sets of collisional data. This method combines diagnostics for electron temperature, electron density, and excited species densities and kinetic modeling of excited species, from which the electron excitation rate coefficients from one of the 1s states to the other 1s states or to one of 2p or 3p states are determined (states are in Paschen’s notation). This paper reviews the above method—namely the combined diagnostics and modeling in afterglow plasmas. The results from other important approaches, including electron-beam measurement of cross sections, laser pump-probe technique for measuring rate coefficients, and theoretical calculations by R-matrix and distorted-wave models are also discussed. From a comparative study of these results, a fitted mathematical expression of excitation rate coefficients is obtained for the electron temperature range of 1–5 eV, which can be used for the collisional-radiative modeling of low-temperature Ar plasmas. At last, we report the limitations in the present dataset and give some suggestions for future work in this area.

  12. Differential Geometry Based Multiscale Models

    PubMed Central

    Wei, Guo-Wei

    2010-01-01

    Large chemical and biological systems such as fuel cells, ion channels, molecular motors, and viruses are of great importance to the scientific community and public health. Typically, these complex systems in conjunction with their aquatic environment pose a fabulous challenge to theoretical description, simulation, and prediction. In this work, we propose a differential geometry based multiscale paradigm to model complex macromolecular systems, and to put macroscopic and microscopic descriptions on an equal footing. In our approach, the differential geometry theory of surfaces and geometric measure theory are employed as a natural means to couple the macroscopic continuum mechanical description of the aquatic environment with the microscopic discrete atom-istic description of the macromolecule. Multiscale free energy functionals, or multiscale action functionals are constructed as a unified framework to derive the governing equations for the dynamics of different scales and different descriptions. Two types of aqueous macromolecular complexes, ones that are near equilibrium and others that are far from equilibrium, are considered in our formulations. We show that generalized Navier–Stokes equations for the fluid dynamics, generalized Poisson equations or generalized Poisson–Boltzmann equations for electrostatic interactions, and Newton's equation for the molecular dynamics can be derived by the least action principle. These equations are coupled through the continuum-discrete interface whose dynamics is governed by potential driven geometric flows. Comparison is given to classical descriptions of the fluid and electrostatic interactions without geometric flow based micro-macro interfaces. The detailed balance of forces is emphasized in the present work. We further extend the proposed multiscale paradigm to micro-macro analysis of electrohydrodynamics, electrophoresis, fuel cells, and ion channels. We derive generalized Poisson–Nernst–Planck equations that

  13. Differential geometry based multiscale models.

    PubMed

    Wei, Guo-Wei

    2010-08-01

    Large chemical and biological systems such as fuel cells, ion channels, molecular motors, and viruses are of great importance to the scientific community and public health. Typically, these complex systems in conjunction with their aquatic environment pose a fabulous challenge to theoretical description, simulation, and prediction. In this work, we propose a differential geometry based multiscale paradigm to model complex macromolecular systems, and to put macroscopic and microscopic descriptions on an equal footing. In our approach, the differential geometry theory of surfaces and geometric measure theory are employed as a natural means to couple the macroscopic continuum mechanical description of the aquatic environment with the microscopic discrete atomistic description of the macromolecule. Multiscale free energy functionals, or multiscale action functionals are constructed as a unified framework to derive the governing equations for the dynamics of different scales and different descriptions. Two types of aqueous macromolecular complexes, ones that are near equilibrium and others that are far from equilibrium, are considered in our formulations. We show that generalized Navier-Stokes equations for the fluid dynamics, generalized Poisson equations or generalized Poisson-Boltzmann equations for electrostatic interactions, and Newton's equation for the molecular dynamics can be derived by the least action principle. These equations are coupled through the continuum-discrete interface whose dynamics is governed by potential driven geometric flows. Comparison is given to classical descriptions of the fluid and electrostatic interactions without geometric flow based micro-macro interfaces. The detailed balance of forces is emphasized in the present work. We further extend the proposed multiscale paradigm to micro-macro analysis of electrohydrodynamics, electrophoresis, fuel cells, and ion channels. We derive generalized Poisson-Nernst-Planck equations that are

  14. Differential geometry based multiscale models.

    PubMed

    Wei, Guo-Wei

    2010-08-01

    Large chemical and biological systems such as fuel cells, ion channels, molecular motors, and viruses are of great importance to the scientific community and public health. Typically, these complex systems in conjunction with their aquatic environment pose a fabulous challenge to theoretical description, simulation, and prediction. In this work, we propose a differential geometry based multiscale paradigm to model complex macromolecular systems, and to put macroscopic and microscopic descriptions on an equal footing. In our approach, the differential geometry theory of surfaces and geometric measure theory are employed as a natural means to couple the macroscopic continuum mechanical description of the aquatic environment with the microscopic discrete atomistic description of the macromolecule. Multiscale free energy functionals, or multiscale action functionals are constructed as a unified framework to derive the governing equations for the dynamics of different scales and different descriptions. Two types of aqueous macromolecular complexes, ones that are near equilibrium and others that are far from equilibrium, are considered in our formulations. We show that generalized Navier-Stokes equations for the fluid dynamics, generalized Poisson equations or generalized Poisson-Boltzmann equations for electrostatic interactions, and Newton's equation for the molecular dynamics can be derived by the least action principle. These equations are coupled through the continuum-discrete interface whose dynamics is governed by potential driven geometric flows. Comparison is given to classical descriptions of the fluid and electrostatic interactions without geometric flow based micro-macro interfaces. The detailed balance of forces is emphasized in the present work. We further extend the proposed multiscale paradigm to micro-macro analysis of electrohydrodynamics, electrophoresis, fuel cells, and ion channels. We derive generalized Poisson-Nernst-Planck equations that are

  15. Guide to APA-Based Models

    NASA Technical Reports Server (NTRS)

    Robins, Robert E.; Delisi, Donald P.

    2008-01-01

    In Robins and Delisi (2008), a linear decay model, a new IGE model by Sarpkaya (2006), and a series of APA-Based models were scored using data from three airports. This report is a guide to the APA-based models.

  16. Analysis of two scenarios for the early optical emission of the gamma-ray burst afterglows 990123 and 021211

    NASA Astrophysics Data System (ADS)

    Panaitescu, A.; Kumar, P.

    2004-09-01

    The optical light curves of gamma-ray burst (GRB) afterglows 990123 and 021211 exhibit a steep decay at 100-600 s after the burst, the decay becoming slower after about 10 min. We investigate two scenarios for the fast decaying early optical emission of these GRB afterglows. In the reverse-forward shock scenario, this emission arises in the reverse shock crossing the GRB ejecta, the mitigation of the light-curve decay occurring when the forward shock emission overtakes that from the reverse shock. Both a homogeneous and wind-like circumburst medium are considered. In the wind-bubble scenario, the steeply decaying, early optical emission arises from the forward shock interacting with a r-2 bubble, with a negligible contribution from the reverse shock, the slower decay starting when the blast wave reaches the bubble termination shock and enters a homogeneous region of the circumburst medium. We determine the shock microphysical parameters, ejecta kinetic energy and circumburst density, which accommodate the radio and optical measurements of the GRB afterglows 990123 and 021211. We find that, for a homogeneous medium, the radio and optical emissions of the afterglow 990123 can be accommodated by the reverse-forward shock scenario if the microphysical parameters behind the two shocks differ substantially. A wind-like circumburst medium also allows the reverse-forward shock scenario to account for the radio and optical properties of the afterglows 990123 and 021211, but the required wind densities are at least 10 times smaller than those of Galactic Wolf-Rayet stars. The wind-bubble scenario requires a variation of the microphysical parameters when the afterglow fireball reaches the wind termination shock, which seems a contrived feature.

  17. Evidence for a Canonical GRB Afterglow Light Curve in the Swift/XRT Data

    SciTech Connect

    Nousek, J.A.; Kouveliotou, C.; Grupe, D.; Page, K.; Granot, J.; Ramirez-Ruiz, E.; Patel, S.K.; Burrows, D.N.; Mangano, V.; Barthelmy, S.; Beardmore, A.P.; Campana, S.; Capalbi, M.; Chincarini, G.; Cusumano, G.; Falcone, A.D.; Gehrels, N.; Giommi, P.; Goad, M.; Godet, O.; Hurkett, C.; /Penn State U., Astron. Astrophys. /NASA, Marshall /Leicester U. /KIPAC, Menlo Park /Princeton, Inst. Advanced Study /NASA, Marshall /IASF, Palermo /Brera Observ. /Frascati /Milan Bicocca U. /NASA, Goddard

    2005-08-17

    We present new observations of the early X-ray afterglows of the first 27 gamma-ray bursts (GRBs) detected with the Swift X-ray Telescope (XRT). The early X-ray afterglows show a canonical behavior, where the light curve broadly consists of three distinct power law segments: (1) an initial very steep decay ({infinity} t{sup -a} with 3 {approx}< a{sub 1} {approx}< 5) , followed by (2) a very shallow decay (0.2 {approx}< a{sub 2} {approx}< 0.8), and finally (3) a somewhat steeper decay (1 {approx}< a{sub 3} {approx}< 1.5). These power law segments are separated by two corresponding break times, 300 s {approx}< t{sub break,1} {approx}< 500 s and 10{sup 3} s {approx}< t{sub break,2} {approx}< 10{sup 4} s. On top of this canonical behavior of the early X-ray light curve, many events have superimposed X-ray flares, which are most likely caused by internal shocks due to long lasting sporadic activity of the central engine, up to several hours after the GRB. We find that the initial steep decay is consistent with it being the tail of the prompt emission, from photons that are radiated at large angles relative to our line of sight. The first break in the light curve (t{sub break,1}) takes place when the forward shock emission becomes dominant, with the intermediate shallow flux decay (a{sub 2}) likely caused by the continuous energy injection into the external shock. When this energy injection stops, a second break is then observed in the light curve (t{sub break,2}). This energy injection increases the energy of the afterglow shock by at least a factor of f {approx}> 4, and augments the already severe requirements for the efficiency of the prompt gamma-ray emission.

  18. Kitaev models based on unitary quantum groupoids

    SciTech Connect

    Chang, Liang

    2014-04-15

    We establish a generalization of Kitaev models based on unitary quantum groupoids. In particular, when inputting a Kitaev-Kong quantum groupoid H{sub C}, we show that the ground state manifold of the generalized model is canonically isomorphic to that of the Levin-Wen model based on a unitary fusion category C. Therefore, the generalized Kitaev models provide realizations of the target space of the Turaev-Viro topological quantum field theory based on C.

  19. EPR-based material modelling of soils

    NASA Astrophysics Data System (ADS)

    Faramarzi, Asaad; Alani, Amir M.

    2013-04-01

    In the past few decades, as a result of the rapid developments in computational software and hardware, alternative computer aided pattern recognition approaches have been introduced to modelling many engineering problems, including constitutive modelling of materials. The main idea behind pattern recognition systems is that they learn adaptively from experience and extract various discriminants, each appropriate for its purpose. In this work an approach is presented for developing material models for soils based on evolutionary polynomial regression (EPR). EPR is a recently developed hybrid data mining technique that searches for structured mathematical equations (representing the behaviour of a system) using genetic algorithm and the least squares method. Stress-strain data from triaxial tests are used to train and develop EPR-based material models for soil. The developed models are compared with some of the well-known conventional material models and it is shown that EPR-based models can provide a better prediction for the behaviour of soils. The main benefits of using EPR-based material models are that it provides a unified approach to constitutive modelling of all materials (i.e., all aspects of material behaviour can be implemented within a unified environment of an EPR model); it does not require any arbitrary choice of constitutive (mathematical) models. In EPR-based material models there are no material parameters to be identified. As the model is trained directly from experimental data therefore, EPR-based material models are the shortest route from experimental research (data) to numerical modelling. Another advantage of EPR-based constitutive model is that as more experimental data become available, the quality of the EPR prediction can be improved by learning from the additional data, and therefore, the EPR model can become more effective and robust. The developed EPR-based material models can be incorporated in finite element (FE) analysis.

  20. LOW-RESOLUTION SPECTROSCOPY OF GAMMA-RAY BURST OPTICAL AFTERGLOWS: BIASES IN THE SWIFT SAMPLE AND CHARACTERIZATION OF THE ABSORBERS

    SciTech Connect

    Fynbo, J. P. U.; Malesani, D.; Vreeswijk, P. M.; Hjorth, J.; Sollerman, J.; Thoene, C. C.; Jakobsson, P.; Bjoernsson, G.; De Cia, A.; Prochaska, J. X.; Nardini, M.; Chen, H.-W.; Bloom, J. S.; Castro-Tirado, A. J.; Gorosabel, J.; Christensen, L.; Fruchter, A. S.

    2009-12-01

    We present a sample of 77 optical afterglows (OAs) of Swift detected gamma-ray bursts (GRBs) for which spectroscopic follow-up observations have been secured. Our first objective is to measure the redshifts of the bursts. For the majority (90%) of the afterglows, the redshifts have been determined from the spectra. We provide line lists and equivalent widths (EWs) for all detected lines redward of Ly{alpha} covered by the spectra. In addition to the GRB absorption systems, these lists include line strengths for a total of 33 intervening absorption systems. We discuss to what extent the current sample of Swift bursts with OA spectroscopy is a biased subsample of all Swift detected GRBs. For that purpose we define an X-ray-selected statistical sample of Swift bursts with optimal conditions for ground-based follow-up from the period 2005 March to 2008 September; 146 bursts fulfill our sample criteria. We derive the redshift distribution for the statistical (X-ray selected) sample and conclude that less than 18% of Swift bursts can be at z > 7. We compare the high-energy properties (e.g., {gamma}-ray (15-350 keV) fluence and duration, X-ray flux, and excess absorption) for three subsamples of bursts in the statistical sample: (1) bursts with redshifts measured from OA spectroscopy; (2) bursts with detected optical and/or near-IR afterglow, but no afterglow-based redshift; and (3) bursts with no detection of the OA. The bursts in group (1) have slightly higher {gamma}-ray fluences and higher X-ray fluxes and significantly less excess X-ray absorption than bursts in the other two groups. In addition, the fractions of dark bursts, defined as bursts with an optical to X-ray slope {beta}{sub OX} < 0.5, is 14% in group (1), 38% in group (2), and >39% in group (3). For the full sample, the dark burst fraction is constrained to be in the range 25%-42%. From this we conclude that the sample of GRBs with OA spectroscopy is not representative for all Swift bursts, most likely due

  1. Testing Strategies for Model-Based Development

    NASA Technical Reports Server (NTRS)

    Heimdahl, Mats P. E.; Whalen, Mike; Rajan, Ajitha; Miller, Steven P.

    2006-01-01

    This report presents an approach for testing artifacts generated in a model-based development process. This approach divides the traditional testing process into two parts: requirements-based testing (validation testing) which determines whether the model implements the high-level requirements and model-based testing (conformance testing) which determines whether the code generated from a model is behaviorally equivalent to the model. The goals of the two processes differ significantly and this report explores suitable testing metrics and automation strategies for each. To support requirements-based testing, we define novel objective requirements coverage metrics similar to existing specification and code coverage metrics. For model-based testing, we briefly describe automation strategies and examine the fault-finding capability of different structural coverage metrics using tests automatically generated from the model.

  2. EARLY-TIME VLA OBSERVATIONS AND BROADBAND AFTERGLOW ANALYSIS OF THE FERMI/LAT DETECTED GRB 130907A

    SciTech Connect

    Veres, Péter; Corsi, Alessandra; Frail, Dale A.; Cenko, S. Bradley; Perley, Daniel A.

    2015-09-01

    We present multi-wavelength observations of the hyper-energetic gamma-ray burst (GRB) 130907A, a Swift-discovered burst with early radio observations starting at ≈4 hr after the γ-ray trigger. GRB 130907A was also detected by the Fermi/LAT instrument and at late times showed a strong spectral evolution in X-rays. We focus on the early-time radio observations, especially at >10 GHz, to attempt to identify reverse shock signatures. While our radio follow-up of GRB 130907A ranks among the earliest observations of a GRB with the Karl G. Jansky Very Large Array, we did not see an unambiguous signature of a reverse shock. While a model with both reverse and forward shock can correctly describe the observations, the data is not constraining enough to decide upon the presence of the reverse-shock component. We model the broadband data using a simple forward-shock synchrotron scenario with a transition from a wind environment to a constant density interstellar medium (ISM) in order to account for the observed features. Within the confines of this model, we also derive the underlying physical parameters of the fireball, which are within typical ranges except for the wind density parameter (A{sub *}), which is higher than those for bursts with wind-ISM transition, but typical for the general population of bursts. We note the importance of early-time radio observations of the afterglow (and of well-sampled light curves) for unambiguously identifying the potential contribution of the reverse shock.

  3. Emission and afterglow properties of an expanding RF plasma with nonuniform neutral gas density

    NASA Astrophysics Data System (ADS)

    Chaplin, Vernon H.; Bellan, Paul M.

    2016-08-01

    We describe some notable aspects of the light emission and afterglow properties in pulsed, high-density ( 1018-1020 m-3 ) argon inductively coupled discharges initiated following fast gas injection. The plasma was created in a long, narrow discharge tube and then expanded downstream of the radiofrequency (RF) antenna into a large chamber. Fast camera images of the expanding plasma revealed a multi-phase time-dependent emission pattern that did not follow the ion density distribution. Dramatic differences in visible brightness were observed between discharges with and without an externally applied magnetic field. These phenomena were studied by tracking excited state populations using passive emission spectroscopy and are discussed in terms of the distinction between ionizing and recombining phase plasmas. Additionally, a method is presented for inferring the unknown neutral gas pressure in the discharge tube from the time-dependent visible and infrared emission measured by a simple photodiode placed near the antenna. In magnetized discharges created with fast gas injection, the downstream ion density rose by Δni˜1018 m-3 in the first ˜100 μs after the RF power was turned off. The conditions conducive to this afterglow density rise are investigated in detail, and the effect is tentatively attributed to pooling ionization.

  4. A Crystalline Mesolamellar Gallium Phosphate with Zwitterionic-type Templates Exhibiting Green Afterglow Property.

    PubMed

    Huang, Hui-Lin; Huang, Yu-Ting; Wang, Sue-Lein

    2016-07-18

    We synthesized a unique layer structure of gallium phosphates containing zwitterionic-type templates under mild hydrothermal reactions. The zwitterionic-type templates, formed of long-alkyl-chain diamine cations and biphenyldicarboxylate anions, resided upright between adjacent layers, propping the interlayer distance up to 2.2 nm. For the first time, the mesoscale interlayer templates were sufficiently well-ordered to afford elucidation to the atomic-level. The mesolamellar (HDADD)2(BPDC)0.5[Ga3(OH)2(HPO4)4] (1; DADD = 1,12-diaminododecane, BPDC = 4,4'-biphenyldicarboxylate) was composed of inorganic layers built up exclusively with a unique type of heptameric unit which featured an unprecedented trimeric cluster of [Ga3(OH)2O12]. Unexpectedly, compound 1 possessed an unusual green afterglow. To interpret the interesting photoluminescence (PL) property, three other low-dimensional structures related to 1 were prepared as well. The data from PL and electron paramagnetic resonance indicated that the afterglow was mainly attributed to lattice defects and the orientations of BPDC. PMID:27367262

  5. Multiwavelength Observations of GRB 110731A: GeV Emission from Onset to Afterglow

    NASA Astrophysics Data System (ADS)

    Ackermann, M.; Ajello, M.; Asano, K.; Baldini, L.; Barbiellini, G.; Baring, M. G.; Bastieri, D.; Bellazzini, R.; Blandford, R. D.; Bonamente, E.; Borgland, A. W.; Bottacini, E.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Cecchi, C.; Charles, E.; Chaves, R. C. G.; Chekhtman, A.; Chiang, J.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Conrad, J.; Cutini, S.; D'Ammando, F.; de Angelis, A.; de Palma, F.; Dermer, C. D.; Silva, E. do Couto e.; Drell, P. S.; Drlica-Wagner, A.; Favuzzi, C.; Fegan, S. J.; Focke, W. B.; Franckowiak, A.; Fukazawa, Y.; Fusco, P.; Gargano, F.; Gasparrini, D.; Gehrels, N.; Giglietto, N.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Granot, J.; Greiner, J.; Grenier, I. A.; Grove, J. E.; Guiriec, S.; Hadasch, D.; Hanabata, Y.; Hayashida, M.; Hays, E.; Hughes, R. E.; Jackson, M. S.; Jogler, T.; Jóhannesson, G.; Johnson, A. S.; Knödlseder, J.; Kocevski, D.; Kuss, M.; Lande, J.; Larsson, S.; Latronico, L.; Longo, F.; Loparco, F.; Lovellette, M. N.; Lubrano, P.; Mazziotta, M. N.; McEnery, J. E.; Mehault, J.; Mészáros, P.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Monte, C.; Monzani, M. E.; Moretti, E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Naumann-Godo, M.; Norris, J. P.; Nuss, E.; Nymark, T.; Ohno, M.; Ohsugi, T.; Omodei, N.; Orienti, M.; Orlando, E.; Paneque, D.; Perkins, J. S.; Pesce-Rollins, M.; Piron, F.; Pivato, G.; Racusin, J. L.; Rainò, S.; Rando, R.; Razzano, M.; Razzaque, S.; Reimer, A.; Reimer, O.; Romoli, C.; Roth, M.; Ryde, F.; Sanchez, D. A.; Sgrò, C.; Siskind, E. J.; Sonbas, E.; Spinelli, P.; Stamatikos, M.; Takahashi, H.; Tanaka, T.; Thayer, J. G.; Thayer, J. B.; Tibaldo, L.; Tinivella, M.; Tosti, G.; Troja, E.; Usher, T. L.; Vandenbroucke, J.; Vasileiou, V.; Vianello, G.; Vitale, V.; Waite, A. P.; Winer, B. L.; Wood, K. S.; Yang, Z.; Gruber, D.; Bhat, P. N.; Bissaldi, E.; Briggs, M. S.; Burgess, J. M.; Connaughton, V.; Foley, S.; Kippen, R. M.; Kouveliotou, C.; McBreen, S.; McGlynn, S.; Paciesas, W. S.; Pelassa, V.; Preece, R.; Rau, A.; van der Horst, A. J.; von Kienlin, A.; Kann, D. A.; Filgas, R.; Klose, S.; Krühler, T.; Fukui, A.; Sako, T.; Tristram, P. J.; Oates, S. R.; Ukwatta, T. N.; Littlejohns, O.

    2013-02-01

    We report on the multiwavelength observations of the bright, long gamma-ray burst GRB 110731A, by the Fermi and Swift observatories, and by the MOA and GROND optical telescopes. The analysis of the prompt phase reveals that GRB 110731A shares many features with bright Large Area Telescope bursts observed by Fermi during the first three years on-orbit: a light curve with short time variability across the whole energy range during the prompt phase, delayed onset of the emission above 100 MeV, extra power-law component and temporally extended high-energy emission. In addition, this is the first GRB for which simultaneous GeV, X-ray, and optical data are available over multiple epochs beginning just after the trigger time and extending for more than 800 s, allowing temporal and spectral analysis in different epochs that favor emission from the forward shock in a wind-type medium. The observed temporally extended GeV emission is most likely part of the high-energy end of the afterglow emission. Both the single-zone pair transparency constraint for the prompt signal and the spectral and temporal analysis of the forward-shock afterglow emission independently lead to an estimate of the bulk Lorentz factor of the jet Γ ~ 500-550.

  6. THE UNUSUAL RADIO AFTERGLOW OF THE ULTRA-LONG GAMMA-RAY BURST GRB 130925A

    SciTech Connect

    Horesh, Assaf; Cenko, S. Bradley; Perley, Daniel A.; Kulkarni, S. R.; Hallinan, Gregg; Bellm, Eric

    2015-10-10

    GRB 130925A is one of the recent additions to the growing family of ultra-long gamma-ray bursts (GRBs; T90 ≳1000 s). While the X-ray emission of ultra-long GRBs have been studied extensively in the past, no comprehensive radio data set has been obtained so far. We report here the early discovery of an unusual radio afterglow associated with the ultra-long GRB 130925A. The radio emission peaks at low-frequencies (∼7 GHz) at early times, only 2.2 days after the burst occurred. More notably, the radio spectrum at frequencies above 10 GHz exhibits a rather steep cut-off, compared to other long GRB radio afterglows. This cut-off can be explained if the emitting electrons are either mono-energetic or originate from a rather steep, dN/dE ∝ E{sup −4}, power-law energy distribution. An alternative electron acceleration mechanism may be required to produce such an electron energy distribution. Furthermore, the radio spectrum exhibits a secondary underlying and slowly varying component. This may hint that the radio emission we observed is comprised of emission from both a reverse and a forward shock. We discuss our results in comparison with previous works that studied the unusual X-ray spectrum of this event and discuss the implications of our findings on progenitor scenarios.

  7. REMIR: The REM infrared camera to follow up the early phases of GRBs afterglows

    NASA Astrophysics Data System (ADS)

    Calzoletti, L.; Melandri, A.; Testa, V.; Antonelli, L. A.; Vitali, F.; D'Alessio, F.; di Paola, A.; Zerbi, F. M.; Chincarini, G.; Cunniffe, R.; Jordan, B.; Rodonò, M.; Conconi, P.; Covino, S.; Cutispoto, G.; Molinari, E.; Tosti, G.; Ross/Rem Team

    2005-07-01

    REMIR is a near-infrared camera, covering the 0.95-2.3 μm range with 5 filters (z,J,H,Ks and H2), mounted at one of the Nasmyth foci of the REM (Rapid Eye Mount) telescope. REM is a fully robotic fast-slewing 60 cm telescope, primarily designed to follow-up the early phases of the afterglow of GRBs detected by dedicated instruments onboard satellites (like SWIFT, a satellite entirely dedicated to GRBs science launched the 12 November 2004). Moreover REM hosts a slitless spectrograph covering the range 0.45-0.95 μm, with 30 sample points and with the possibility to perform broad-band V,R,I photometry (ROSS, REM Optical Slitless Spectrograph). The main task of REMIR is to perform realtime NIR observations of GRBs detected by gamma-ray monitors onboard satellites, looking for any possible infrared transient source. As soon as a transient source is detected in the IR images, larger telescopes are promptly alerted to perform early spectroscopy of the afterglow. All the above operations are performed in a fully automatic way and without any human supervision. We present the results of on-site tests that have been done to characterize the REMIR camera and the performances of the dedicated reduction pipeline AQuA (Automatic Quick Analysis), suited for fast transients detection.

  8. Emissive sheath measurements in the afterglow of a radio frequency plasma

    SciTech Connect

    Sheehan, J. P. Hershkowitz, N.; Barnat, E. V.; Weatherford, B. R.; Kaganovich, I. D.

    2014-01-15

    The difference between the plasma potential and the floating potential of a highly emissive planar surface was measured in the afterglow of a radio frequency discharge. A Langmuir probe was used to measure the electron temperature and an emissive probe was used to measure the spatial distribution of the potential using the inflection point in the limit of zero emission technique. Time-resolved measurements were made using the slow-sweep method, a technique for measuring time-resolved current-voltage traces. This was the first time the inflection point in the limit of zero emission was used to make time-resolved measurements. Measurements of the potential profile of the presheath indicate that the potential penetrated approximately 50% farther into the plasma when a surface was emitting electrons. The experiments confirmed a recent kinetic theory of emissive sheaths, demonstrating that late in the afterglow as the plasma electron temperature approached the emitted electron temperature, the emissive sheath potential shrank to zero. However, the difference between the plasma potential and the floating potential of a highly emissive planar surface data appeared to be much less sensitive to the electron temperature ratio than the theory predicts.

  9. Emissive sheath measurements in the afterglow of a radio frequency plasma

    NASA Astrophysics Data System (ADS)

    Sheehan, J. P.; Barnat, E. V.; Weatherford, B. R.; Kaganovich, I. D.; Hershkowitz, N.

    2014-01-01

    The difference between the plasma potential and the floating potential of a highly emissive planar surface was measured in the afterglow of a radio frequency discharge. A Langmuir probe was used to measure the electron temperature and an emissive probe was used to measure the spatial distribution of the potential using the inflection point in the limit of zero emission technique. Time-resolved measurements were made using the slow-sweep method, a technique for measuring time-resolved current-voltage traces. This was the first time the inflection point in the limit of zero emission was used to make time-resolved measurements. Measurements of the potential profile of the presheath indicate that the potential penetrated approximately 50% farther into the plasma when a surface was emitting electrons. The experiments confirmed a recent kinetic theory of emissive sheaths, demonstrating that late in the afterglow as the plasma electron temperature approached the emitted electron temperature, the emissive sheath potential shrank to zero. However, the difference between the plasma potential and the floating potential of a highly emissive planar surface data appeared to be much less sensitive to the electron temperature ratio than the theory predicts.

  10. Electromagnetic afterglows associated with gamma-ray emission coincident with binary black hole merger event GW150914

    NASA Astrophysics Data System (ADS)

    Yamazaki, Ryo; Asano, Katsuaki; Ohira, Yutaka

    2016-05-01

    The Fermi Gamma-ray Burst Monitor reported the possible detection of the gamma-ray counterpart of a binary black hole merger event, GW150914. We show that the gamma-ray emission is caused by a relativistic outflow with Lorentz factor larger than 10. Subsequently, debris outflow pushes the ambient gas to form a shock, which is responsible for the afterglow synchrotron emission. We find that the 1.4 GHz radio flux peaks at {˜ }10^5 s after the burst trigger. If the ambient matter is dense enough, with density larger than {˜ }10^{-2} cm^{-3}, then the peak radio flux is {˜ }0.1 mJy, which is detectable with radio telescopes such as the Very Large Array. The optical afterglow peaks earlier than the radio, and if the ambient matter density is larger than {˜ }0.1 cm^{-3}, the optical flux is detectable with large telescopes such as the Subaru Hyper Suprime-Cam. To reveal the currently unknown mechanisms of the outflow and its gamma-ray emission associated with the binary black hole merger event, follow-up electromagnetic observations of afterglows are important. Detection of the afterglow will localize the sky position of the gravitational wave and gamma-ray emissions, and it will support the physical association between them.

  11. The Growth, Polarization and Motion of the Radio Afterglow from the Giant Flare from SGR 1806-20

    NASA Technical Reports Server (NTRS)

    Taylor, G. B.; Gelfand, J. D.; Gaensler, B. M.; Granot, J.; Kouveliotou, C.; Fender, R. P.; Ramirez-Ruiz, E.; Eichler, D.; Lyubarsky, Y. E.; Garrett, M.

    2005-01-01

    The extraordinary giant flare (GF) of 2004 December 27 from the soft gamma repeater (SGR) 1806-20 was followed by a bright radio afterglow. We present an analysis of VLA observations of this radio afterglow from SGR 1806-20, consisting of previously reported 8.5 GHz data covering days 7 to 20 after the GF, plus new observations at 8.5 and 22 GHz from day 24 to 81. We find a deceleration in the expansion, from approximately 4.5 mas/day to less than 2.5 mas/day. The time of deceleration is roughly coincident with the rebrightening in the radio light curve, as expected to result when the ejecta from the GF sweeps up enough of the external medium, and transitions from a coasting phase to the Sedov-Taylor regime. The radio afterglow is elongated and maintains a 2:l axis ratio with an average position angle of -40 degrees (north through east), oriented perpendicular to the average intrinsic linear polarization angle. We also report on the discovery of motion in the flux centroid of the afterglow, at an average velocity of 0.26 plus or minus 0.03 c (assuming a distance of 15 kpc) at a position angle of -40 degrees. This motion, in combination with the growth and polarization measurements, suggests an initially asymmetric outflow, mainly from one side of the magnetar.

  12. GAMMA-RAY BURST AFTERGLOW LIGHT CURVES FROM A LORENTZ-BOOSTED SIMULATION FRAME AND THE SHAPE OF THE JET BREAK

    SciTech Connect

    Van Eerten, Hendrik; MacFadyen, Andrew

    2013-04-20

    The early stages of decelerating gamma-ray burst (GRB) afterglow jets have been notoriously difficult to resolve numerically using two-dimensional hydrodynamical simulations even at very high resolution, due to the extreme thinness of the blast wave and high outflow Lorentz factors. However, these resolution issues can be avoided by performing the simulations in a boosted frame, which makes it possible to calculate afterglow light curves from numerically computed flows in sufficient detail to accurately quantify the shape of the jet break and the post-break steepening of the light curve. Here, we study afterglow jet breaks for jets with opening angles of 0.05, 0.1, and 0.2 radians decelerating in a surrounding medium of constant density, observed at various angles ranging from on-axis to the edge of the jet. A single set of scale-invariant functions describing the time evolution of afterglow synchrotron spectral break frequencies and peak flux, depending only on jet opening angle and observer angle, are all that is needed to reconstruct light curves for arbitrary explosion energy, circumburst density and synchrotron particle distribution power law slope p. These functions are presented in the paper. Their time evolutions change directly following the jet break, although an earlier reported temporary post-break steepening of the cooling break is found to have been resolution-induced. We compare synthetic light curves to fit functions using sharp power law breaks as well as smooth power law transitions. We confirm our earlier finding that the measured jet break time is very sensitive to the angle of the observer and can be postponed significantly. We find that the difference in temporal indices across the jet break is larger than theoretically anticipated and is about -(0.5 + 0.5p) below the cooling break and about -(0.25 + 0.5p) above the cooling break, both leading to post-break slopes of roughly about 0.25 - 1.3p, although different observer angles, jet opening

  13. Sequential afterglow processing and non-contact Corona-Kelvin metrology of 4H-silicon carbide

    NASA Astrophysics Data System (ADS)

    Short, Eugene L., III

    Silicon carbide (SiC) is a wide band-gap semiconductor with advantageous electrical and thermal properties making it attractive for high temperature and power applications. However, difficulties with oxide/SiC structures have posed challenges to the development of practical MOS-type devices. Surface conditioning and oxidation of 4H-SiC were investigated using a novel sequential afterglow processing approach combined with the unique capabilities of non-contact corona-Kelvin metrology. The use of remote plasma assisted thermal oxidation facilitated film growth at low temperature and pressure with the flexibility of sequential in-situ processing options including pre-oxidation surface conditioning. Corona-Kelvin metrology (C-KM) provided a fast, nondestructive method for electrical evaluation of oxide films and semiconductor surfaces. Non-contact C-KM oxide capacitance-voltage characteristics combined with direct measurement of SiC surfaces using C-KM depletion surface barrier monitoring and XPS analysis of surface chemistry were interpreted relating the impact of afterglow conditioning on the surface and its influence on subsequent oxide thin film growth. Afterglow oxide films of thicknesses 50--500 A were fabricated on SiC epi-layers at low growth temperatures in the range 600--850°C, an achievement not possible using conventional atmospheric oxidation techniques. The inclusion of pre-oxidation surface conditioning in forming gas (N2:H2)* afterglow was found to produce an increase in oxide growth rate (10--25%) and a significant improvement in oxide film thickness uniformity. Analysis of depletion voltage transients on conditioned SiC surfaces revealed the highest degree of surface passivation, uniformity, and elimination of sources of charge compensation accomplished by the (N2:H2)* afterglow treatment for 20 min. at 600--700°C compared to other conditioning variations. The state of surface passivation was determined to be very stable and resilient when exposed

  14. Multiscale agent-based consumer market modeling.

    SciTech Connect

    North, M. J.; Macal, C. M.; St. Aubin, J.; Thimmapuram, P.; Bragen, M.; Hahn, J.; Karr, J.; Brigham, N.; Lacy, M. E.; Hampton, D.; Decision and Information Sciences; Procter & Gamble Co.

    2010-05-01

    Consumer markets have been studied in great depth, and many techniques have been used to represent them. These have included regression-based models, logit models, and theoretical market-level models, such as the NBD-Dirichlet approach. Although many important contributions and insights have resulted from studies that relied on these models, there is still a need for a model that could more holistically represent the interdependencies of the decisions made by consumers, retailers, and manufacturers. When the need is for a model that could be used repeatedly over time to support decisions in an industrial setting, it is particularly critical. Although some existing methods can, in principle, represent such complex interdependencies, their capabilities might be outstripped if they had to be used for industrial applications, because of the details this type of modeling requires. However, a complementary method - agent-based modeling - shows promise for addressing these issues. Agent-based models use business-driven rules for individuals (e.g., individual consumer rules for buying items, individual retailer rules for stocking items, or individual firm rules for advertizing items) to determine holistic, system-level outcomes (e.g., to determine if brand X's market share is increasing). We applied agent-based modeling to develop a multi-scale consumer market model. We then conducted calibration, verification, and validation tests of this model. The model was successfully applied by Procter & Gamble to several challenging business problems. In these situations, it directly influenced managerial decision making and produced substantial cost savings.

  15. The Strength-Based Counseling Model

    ERIC Educational Resources Information Center

    Smith, Elsie J.

    2006-01-01

    This article proposes a strength-based model for counseling at-risk youth. The author presents the assumptions, basic concepts, and values of the strength perspective in counseling and offers strength categories as a conceptual model for viewing clients' behavior. Propositions leading toward a theory of strength-based counseling and stages of this…

  16. An agent based model of genotype editing

    SciTech Connect

    Rocha, L. M.; Huang, C. F.

    2004-01-01

    This paper presents our investigation on an agent-based model of Genotype Editing. This model is based on several characteristics that are gleaned from the RNA editing system as observed in several organisms. The incorporation of editing mechanisms in an evolutionary agent-based model provides a means for evolving agents with heterogenous post-transcriptional processes. The study of this agent-based genotype-editing model has shed some light into the evolutionary implications of RNA editing as well as established an advantageous evolutionary computation algorithm for machine learning. We expect that our proposed model may both facilitate determining the evolutionary role of RNA editing in biology, and advance the current state of research in agent-based optimization.

  17. Model-based internal wave processing

    SciTech Connect

    Candy, J.V.; Chambers, D.H.

    1995-06-09

    A model-based approach is proposed to solve the oceanic internal wave signal processing problem that is based on state-space representations of the normal-mode vertical velocity and plane wave horizontal velocity propagation models. It is shown that these representations can be utilized to spatially propagate the modal (dept) vertical velocity functions given the basic parameters (wave numbers, Brunt-Vaisala frequency profile etc.) developed from the solution of the associated boundary value problem as well as the horizontal velocity components. Based on this framework, investigations are made of model-based solutions to the signal enhancement problem for internal waves.

  18. Gradient-based model calibration with proxy-model assistance

    NASA Astrophysics Data System (ADS)

    Burrows, Wesley; Doherty, John

    2016-02-01

    Use of a proxy model in gradient-based calibration and uncertainty analysis of a complex groundwater model with large run times and problematic numerical behaviour is described. The methodology is general, and can be used with models of all types. The proxy model is based on a series of analytical functions that link all model outputs used in the calibration process to all parameters requiring estimation. In enforcing history-matching constraints during the calibration and post-calibration uncertainty analysis processes, the proxy model is run for the purposes of populating the Jacobian matrix, while the original model is run when testing parameter upgrades; the latter process is readily parallelized. Use of a proxy model in this fashion dramatically reduces the computational burden of complex model calibration and uncertainty analysis. At the same time, the effect of model numerical misbehaviour on calculation of local gradients is mitigated, this allowing access to the benefits of gradient-based analysis where lack of integrity in finite-difference derivatives calculation would otherwise have impeded such access. Construction of a proxy model, and its subsequent use in calibration of a complex model, and in analysing the uncertainties of predictions made by that model, is implemented in the PEST suite.

  19. Image-Based Flow Modeling

    NASA Astrophysics Data System (ADS)

    Dillard, Seth; Mousel, John; Buchholz, James; Udaykumar, H. S.

    2009-11-01

    A preliminary method has been developed to model complex moving boundaries interacting with fluids in two dimensions using video files. Image segmentation techniques are employed to generate sharp object interfaces which are cast as level sets embedded in a Cartesian flow domain. In this way, boundary evolution is effected directly through imagery rather than by way of functional approximation. Videos of an American eel swimming in a water tunnel apparatus and a guinea pig duodenum undergoing peristaltic contractions in vitro serve as external and internal flow examples, which are evaluated for wake structure and mixing efficacy, respectively.

  20. I-V characteristics of the Langmuir probe in flowing afterglow plasmas

    NASA Astrophysics Data System (ADS)

    Shun'ko, E. V.

    2003-04-01

    The specific features of the probe I-V characteristics in flowing-afterglow plasmas are studied experimentally and in theory. As it was found at a probe potential equal to the plasma one, V=0, an electron concentration in a probe vicinity (and a probe current) is decreased due to a predominant outflow of the electrons into an electrical circuit of the probe from the probe vicinity. The expression allowing one to reconstruct the undisturbed-by-probe electron concentration from only experimental data is derived. The reconstructed values of the electron concentration enable one to find from the experiments the semiempiric expressions allowing to describe quantitatively the behavior of the probe I-V characteristics at the electron-attracting as well as at the ion-attracting potential, respectively. The expressions found (both for electron-attracting and ion-attracting potential) include the "separating length," which merely is the Langmuir length with a factor equal to the square root of the electron mass over the ion mass ratio for two-component plasma. The intermediate part of the probe I-V characteristics is discovered for probes operating with afterglow plasmas. This intermediate part is described in terms of the experimental parameter L0 having a dimension of the length (presumably electron-orbital length). The value of the parameter L0 does not depend on plasma parameters to within the ranges of plasma parameter variations for experimentally investigated plasmas as it was found. The experiments were performed with two cylindrical probes of 10 and 25 μm diam and ˜3 mm lengths in the experimentally investigated ranges of the afterglow plasma parameters: 105 cm-3

  1. Requirements based system risk modeling

    NASA Technical Reports Server (NTRS)

    Meshkat, Leila; Cornford, Steven; Feather, Martin

    2004-01-01

    The problem that we address in this paper is assessing the expected degree of success of the system or mission based on the degree to which each requirement is satisfied and the relative weight of the requirements. We assume a complete list of the requirements, the relevant risk elements and their probability of occurrence and the quantified effect of the risk elements on the requirements. In order to assess the degree to which each requirement is satisfied, we need to determine the effect of the various risk elements on the requirement.

  2. Measurement-based reliability/performability models

    NASA Technical Reports Server (NTRS)

    Hsueh, Mei-Chen

    1987-01-01

    Measurement-based models based on real error-data collected on a multiprocessor system are described. Model development from the raw error-data to the estimation of cumulative reward is also described. A workload/reliability model is developed based on low-level error and resource usage data collected on an IBM 3081 system during its normal operation in order to evaluate the resource usage/error/recovery process in a large mainframe system. Thus, both normal and erroneous behavior of the system are modeled. The results provide an understanding of the different types of errors and recovery processes. The measured data show that the holding times in key operational and error states are not simple exponentials and that a semi-Markov process is necessary to model the system behavior. A sensitivity analysis is performed to investigate the significance of using a semi-Markov process, as opposed to a Markov process, to model the measured system.

  3. Model-Based Prognostics of Hybrid Systems

    NASA Technical Reports Server (NTRS)

    Daigle, Matthew; Roychoudhury, Indranil; Bregon, Anibal

    2015-01-01

    Model-based prognostics has become a popular approach to solving the prognostics problem. However, almost all work has focused on prognostics of systems with continuous dynamics. In this paper, we extend the model-based prognostics framework to hybrid systems models that combine both continuous and discrete dynamics. In general, most systems are hybrid in nature, including those that combine physical processes with software. We generalize the model-based prognostics formulation to hybrid systems, and describe the challenges involved. We present a general approach for modeling hybrid systems, and overview methods for solving estimation and prediction in hybrid systems. As a case study, we consider the problem of conflict (i.e., loss of separation) prediction in the National Airspace System, in which the aircraft models are hybrid dynamical systems.

  4. On conductance-based neural field models

    PubMed Central

    Pinotsis, Dimitris A.; Leite, Marco; Friston, Karl J.

    2013-01-01

    This technical note introduces a conductance-based neural field model that combines biologically realistic synaptic dynamics—based on transmembrane currents—with neural field equations, describing the propagation of spikes over the cortical surface. This model allows for fairly realistic inter-and intra-laminar intrinsic connections that underlie spatiotemporal neuronal dynamics. We focus on the response functions of expected neuronal states (such as depolarization) that generate observed electrophysiological signals (like LFP recordings and EEG). These response functions characterize the model's transfer functions and implicit spectral responses to (uncorrelated) input. Our main finding is that both the evoked responses (impulse response functions) and induced responses (transfer functions) show qualitative differences depending upon whether one uses a neural mass or field model. Furthermore, there are differences between the equivalent convolution and conductance models. Overall, all models reproduce a characteristic increase in frequency, when inhibition was increased by increasing the rate constants of inhibitory populations. However, convolution and conductance-based models showed qualitatively different changes in power, with convolution models showing decreases with increasing inhibition, while conductance models show the opposite effect. These differences suggest that conductance based field models may be important in empirical studies of cortical gain control or pharmacological manipulations. PMID:24273508

  5. THE AFTERGLOW AND ULIRG HOST GALAXY OF THE DARK SHORT GRB 120804A

    SciTech Connect

    Berger, E.; Zauderer, B. A.; Margutti, R.; Laskar, T.; Fong, W.; Chornock, R.; Dupuy, T. J.; Levan, A.; Tunnicliffe, R. L.; Mangano, V.; Fox, D. B.; Tanvir, N. R.; Menten, K. M.; Hjorth, J.; Roth, K.

    2013-03-10

    We present the optical discovery and subarcsecond optical and X-ray localization of the afterglow of the short GRB 120804A, as well as optical, near-IR, and radio detections of its host galaxy. X-ray observations with Swift/XRT, Chandra, and XMM-Newton extending to {delta}t Almost-Equal-To 19 days reveal a single power-law decline. The optical afterglow is faint, and comparison to the X-ray flux indicates that GRB 120804A is ''dark'', with a rest-frame extinction of A {sup host}{sub V} Almost-Equal-To 2.5 mag (at z = 1.3). The intrinsic neutral hydrogen column density inferred from the X-ray spectrum, N{sub H,{sub int}}(z = 1.3) Almost-Equal-To 2 Multiplication-Sign 10{sup 22} cm{sup -2}, is commensurate with the large extinction. The host galaxy exhibits red optical/near-IR colors. Equally important, JVLA observations at Almost-Equal-To 0.9-11 days reveal a constant flux density of F{sub {nu}}(5.8 GHz) = 35 {+-} 4 {mu}Jy and an optically thin spectrum, unprecedented for GRB afterglows, but suggestive instead of emission from the host galaxy. The optical/near-IR and radio fluxes are well fit with the scaled spectral energy distribution of the local ultraluminous infrared galaxy (ULIRG) Arp 220 at z Almost-Equal-To 1.3, with a resulting star formation rate of x Almost-Equal-To 300 M{sub Sun} yr{sup -1}. The inferred extinction and small projected offset (2.2 {+-} 1.2 kpc) are also consistent with the ULIRG scenario, as is the presence of a companion galaxy at the same redshift and with a separation of about 11 kpc. The limits on radio afterglow emission, in conjunction with the observed X-ray and optical emission, require a circumburst density of n {approx} 10{sup -3} cm{sup -3}, an isotropic-equivalent energy scale of E{sub {gamma},{sub iso}} Almost-Equal-To E{sub K,{sub iso}} Almost-Equal-To 7 Multiplication-Sign 10{sup 51} erg, and a jet opening angle of {theta}{sub j} {approx}> 11 Degree-Sign . The expected fraction of luminous infrared galaxies in the short GRB

  6. A possible macronova in the late afterglow of the long-short burst GRB 060614

    NASA Astrophysics Data System (ADS)

    Yang, Bin; Jin, Zhi-Ping; Li, Xiang; Covino, Stefano; Zheng, Xian-Zhong; Hotokezaka, Kenta; Fan, Yi-Zhong; Piran, Tsvi; Wei, Da-Ming

    2015-06-01

    Long-duration (>2 s) γ-ray bursts that are believed to originate from the death of massive stars are expected to be accompanied by supernovae. GRB 060614, that lasted 102 s, lacks a supernova-like emission down to very stringent limits and its physical origin is still debated. Here we report the discovery of near-infrared bump that is significantly above the regular decaying afterglow. This red bump is inconsistent with even the weakest known supernova. However, it can arise from a Li-Paczyński macronova--the radioactive decay of debris following a compact binary merger. If this interpretation is correct, GRB 060614 arose from a compact binary merger rather than from the death of a massive star and it was a site of a significant production of heavy r-process elements. The significant ejected mass favours a black hole-neutron star merger but a double neutron star merger cannot be ruled out.

  7. Plastic Damping of Alfvén Waves in Magnetar Flares and Delayed Afterglow Emission

    NASA Astrophysics Data System (ADS)

    Li, Xinyu; Beloborodov, Andrei M.

    2015-12-01

    Magnetar flares generate Alfvén waves bouncing in the closed magnetosphere with energy up to ∼ {10}46 erg. We show that on a timescale of 10 ms the waves are transmitted into the star and form a compressed packet of high energy density. This packet strongly shears the stellar crust and initiates a plastic flow, heating the crust and melting it hundreds of meters below the surface. A fraction of the deposited plastic heat is eventually conducted to the stellar surface, contributing to the surface afterglow months to years after the flare. A large fraction of heat is lost to neutrino emission or conducted into the core of the neutron star.

  8. Decrease in the etch rate of polymers in the oxygen afterglow with increasing gas flow rate

    NASA Technical Reports Server (NTRS)

    Lerner, N. R.; Wydeven, T.

    1988-01-01

    This paper reports the variation of the etch rate of polymers in the afterglow of a radio frequency discharge in oxygen as a function of total flow rate in the range 2-10 cu cm (STP)/min. The measurements were made at ambient temperature with the O(P-3) concentration held essentially constant. Results are reported on three polymers: cis-polybutadiene, a polybutadiene with 33 percent 1,2 double bonds, and a polybutadiene with 40 percent 1,2 double bonds. It has been observed that the etch rate of these polymers decreases significantly with increasing flow rate, strongly suggesting that the vapor-phase products of polymer degradation contribute to the degradation process.

  9. Nanostructures design by plasma afterglow-assisted oxidation of iron-copper thin films

    NASA Astrophysics Data System (ADS)

    Imam, A.; Boileau, A.; Gries, T.; Ghanbaja, J.; Mangin, D.; Hussein, K.; Sezen, H.; Amati, M.; Belmonte, T.

    2016-05-01

    Oxidizing thin films made of Fe-Cu alloy with an Ar-O2 micro-afterglow operated at atmospheric pressure shows remarkable growth processes. The presence of iron in copper up to about 50% leads to the synthesis of CuO nanostructures (nanowalls, nanotowers and nanowires). Nanotowers show the presence of an amorphous phase trapped between crystalline domains. Beyond 50%, Fe2O3 iron nanoblades are also found. CuO nanowires as small as 5 nm in diameter can be synthesized. Thanks to the presence of patterned domains induced by buckling, it was possible to show that the stress level decreases when the iron content in the alloy increases. Iron blades grow from the inner Fe2O3 layer through the overlying CuO if it is thin enough.

  10. The Giant Flare From SGR 1806-20 And Its Radio Afterglow

    SciTech Connect

    Taylor, G.B.; Granot, J.; /KIPAC, Menlo Park

    2006-09-26

    The multi-wavelength observations of the 2004 December 27 Giant Flare (GF) from SGR 1806-20 and its long-lived radio afterglow are briefly reviewed. The GF appears to have been produced by a dramatic reconfiguration of the magnetic field near the surface of the neutron star, possibly accompanied by fractures in the crust. The explosive release of over 10{sup 46} erg (isotropic equivalent) powered a one-sided mildly relativistic outflow. The outflow produced a new expanding radio nebula, that is still visible over a year after the GF. Also considered are the constraints on the total energy in the GF, the energy and mass in the outflow, and on the external density, as well as possible implications for short {gamma}-ray bursts and potential signatures in high energy neutrinos, photons, or cosmic rays. Some possible future observations of this and other GFs are briefly discussed.

  11. A possible macronova in the late afterglow of the long-short burst GRB 060614.

    PubMed

    Yang, Bin; Jin, Zhi-Ping; Li, Xiang; Covino, Stefano; Zheng, Xian-Zhong; Hotokezaka, Kenta; Fan, Yi-Zhong; Piran, Tsvi; Wei, Da-Ming

    2015-06-11

    Long-duration (>2 s) γ-ray bursts that are believed to originate from the death of massive stars are expected to be accompanied by supernovae. GRB 060614, that lasted 102 s, lacks a supernova-like emission down to very stringent limits and its physical origin is still debated. Here we report the discovery of near-infrared bump that is significantly above the regular decaying afterglow. This red bump is inconsistent with even the weakest known supernova. However, it can arise from a Li-Paczyński macronova--the radioactive decay of debris following a compact binary merger. If this interpretation is correct, GRB 060614 arose from a compact binary merger rather than from the death of a massive star and it was a site of a significant production of heavy r-process elements. The significant ejected mass favours a black hole-neutron star merger but a double neutron star merger cannot be ruled out.

  12. Ground-Based Telescope Parametric Cost Model

    NASA Technical Reports Server (NTRS)

    Stahl, H. Philip; Rowell, Ginger Holmes

    2004-01-01

    A parametric cost model for ground-based telescopes is developed using multi-variable statistical analysis, The model includes both engineering and performance parameters. While diameter continues to be the dominant cost driver, other significant factors include primary mirror radius of curvature and diffraction limited wavelength. The model includes an explicit factor for primary mirror segmentation and/or duplication (i.e.. multi-telescope phased-array systems). Additionally, single variable models based on aperture diameter are derived. This analysis indicates that recent mirror technology advances have indeed reduced the historical telescope cost curve.

  13. Multimode model based defect characterization in composites

    NASA Astrophysics Data System (ADS)

    Roberts, R.; Holland, S.; Gregory, E.

    2016-02-01

    A newly-initiated research program for model-based defect characterization in CFRP composites is summarized. The work utilizes computational models of the interaction of NDE probing energy fields (ultrasound and thermography), to determine 1) the measured signal dependence on material and defect properties (forward problem), and 2) an assessment of performance-critical defect properties from analysis of measured NDE signals (inverse problem). Work is reported on model implementation for inspection of CFRP laminates containing delamination and porosity. Forward predictions of measurement response are presented, as well as examples of model-based inversion of measured data for the estimation of defect parameters.

  14. Developing Grid based infrastructure or climate modeling

    SciTech Connect

    Taylor, J.; Dvorak, M.; Mickelson, S.

    2002-08-15

    In this paper we discuss the development of a high performance climate modeling system as an example of the application of Grid based technology to climate modeling. The climate simulation system at Argonne currently includes a scientific modeling interface (Espresso) written in Java which incorporates Globus middleware to facilitate climate simulations on the Grid. The climate modeling system also includes a high performance version of MM5v3.4 modified for long climate simulations on our 512 processor Linux cluster (Chiba City), an interactive web based tool to facilitate analysis and collaboration via the web, and an enhanced version of the Cave5D software capable of visualizing large climate data sets. We plan to incorporate other climate modeling systems such as the Fast Ocean Atmosphere Model (FOAM) and the National Center for Atmospheric Research's (NCAR) Community Climate Systems Model (CCSM) within Espresso to facilitate their application on computational grids.

  15. Execution-Based Model Checking of Interrupt-Based Systems

    NASA Technical Reports Server (NTRS)

    Drusinsky, Doron; Havelund, Klaus

    2003-01-01

    Execution-based model checking (EMC) is a verification technique based on executing a multi-threaded/multiprocess program repeatedly in a systematic manner in order to explore the different interleavings of the program. This is in contrast to traditional model checking, where a model of a system is analyzed Several execution-based model-checking tools exist at this point, such as for example Verisoft and Java PathFinder. The most common formal specification languages used by EMC tools are un- timed, either just assertions, or linear-time temporal logic (LTL). An alternative verification technique is Runtime Execution Monitoring (REM), which is based on monitor- ing the execution of a program, checking that the execution trace conforms to a requirement specification. The Temporal Rover and DBRover are such tools. They provide a very rich specification language, being an extension of LTL with real-time constraints and time-series. We show how execution-based model checking, combined with runtime execution monitoring, can be used for the verification of a large class of safety critical systems commonly known as interrupt-based systems. The proposed approach is novel in that: (i) it supports model checking of a large class of applications not practically verifiable using conventional EMC tools, (ii) it supports verification of LTL assertions extended with real-time and time-series constraints, and (iii) it supports the verification of custom schedulers.

  16. Distributed Prognostics based on Structural Model Decomposition

    NASA Technical Reports Server (NTRS)

    Daigle, Matthew J.; Bregon, Anibal; Roychoudhury, I.

    2014-01-01

    Within systems health management, prognostics focuses on predicting the remaining useful life of a system. In the model-based prognostics paradigm, physics-based models are constructed that describe the operation of a system and how it fails. Such approaches consist of an estimation phase, in which the health state of the system is first identified, and a prediction phase, in which the health state is projected forward in time to determine the end of life. Centralized solutions to these problems are often computationally expensive, do not scale well as the size of the system grows, and introduce a single point of failure. In this paper, we propose a novel distributed model-based prognostics scheme that formally describes how to decompose both the estimation and prediction problems into independent local subproblems whose solutions may be easily composed into a global solution. The decomposition of the prognostics problem is achieved through structural decomposition of the underlying models. The decomposition algorithm creates from the global system model a set of local submodels suitable for prognostics. Independent local estimation and prediction problems are formed based on these local submodels, resulting in a scalable distributed prognostics approach that allows the local subproblems to be solved in parallel, thus offering increases in computational efficiency. Using a centrifugal pump as a case study, we perform a number of simulation-based experiments to demonstrate the distributed approach, compare the performance with a centralized approach, and establish its scalability. Index Terms-model-based prognostics, distributed prognostics, structural model decomposition ABBREVIATIONS

  17. Gamma-ray Burst Reverse Shock Emission in Early Radio Afterglows

    NASA Astrophysics Data System (ADS)

    Resmi, Lekshmi; Zhang, Bing

    2016-07-01

    Reverse shock (RS) emission from gamma-ray bursts is an important tool in investigating the nature of the ejecta from the central engine. If the magnetization of the ejecta is not high enough to suppress the RS, a strong RS emission component, usually peaking in the optical/IR band early on, would provide an important contribution to early afterglow light curve. In the radio band, synchrotron self-absorption may suppress early RS emission and also delay the RS peak time. In this paper, we calculate the self-absorbed RS emission in the radio band under different dynamical conditions. In particular, we stress that the RS radio emission is subject to self-absorption in both RSs and forward shocks (FSs). We calculate the ratio between the RS to FS flux at the RS peak time for different frequencies, which is a measure of the detectability of the RS emission component. We then constrain the range of physical parameters for a detectable RS, in particular the role of magnetization. We notice that unlike optical RS emission which is enhanced by moderate magnetization, moderately magnetized ejecta do not necessarily produce a brighter radio RS due to the self-absorption effect. For typical parameters, the RS emission component would not be detectable below 1 GHz unless the medium density is very low (e.g., n < 10-3 cm-3 for the interstellar medium and A * < 5 × 10-4 for wind). These predictions can be tested using the afterglow observations from current and upcoming radio facilities such as the Karl G. Jansky Very Large Array, the Low-Frequency Array, the Five Hundred Meter Aperture Spherical Telescope, and the Square Kilometer Array.

  18. Luminosity Correlations for Gamma-Ray Bursts and Implications for Their Prompt and Afterglow Emission Mechanisms

    NASA Astrophysics Data System (ADS)

    Sultana, J.; Kazanas, D.; Fukumura, K.

    2012-10-01

    We present the relation between the (z- and k-corrected) spectral lags, τ, for the standard Swift energy bands 50-100 keV and 100-200 keV and the peak isotropic luminosity, L iso (a relation reported first by Norris et al.), for a subset of 12 long Swift gamma-ray bursts (GRBs) taken from a recent study of this relation by Ukwatta et al. The chosen GRBs are also a subset of the Dainotti et al. sample, a set of Swift GRBs of known redshift, employed in establishing a relation between the (GRB frame) luminosity, LX , of the shallow (or constant) flux portion of the typical X-Ray Telescope GRB-afterglow light curve and the (GRB frame) time of transition to the normal decay rate, T brk. We also present the LX -T brk relation using only the bursts common in the two samples. The two relations exhibit a significant degree of correlation (ρ = -0.65 for the L iso-τ and ρ = -0.88 for the LX -T brk relation) and have surprisingly similar best-fit power-law indices (-1.19 ± 0.17 for L iso-τ and -1.10 ± 0.03 for LX -T brk). Even more surprisingly, we noted that although τ and T brk represent different GRB time variables, it appears that the first relation (L iso-τ) extrapolates into the second one for timescales τ ~= T brk. This fact suggests that these two relations have a common origin, which we conjecture to be kinematic. This relation adds to the recently discovered relations between properties of the prompt and afterglow GRB phases, indicating a much more intimate relation between these two phases than hitherto considered.

  19. Hot blast stove process model and model-based controller

    SciTech Connect

    Muske, K.R.; Howse, J.W.; Hansen, G.A.; Cagliostro, D.J.; Chaubal, P.C.

    1998-12-31

    This paper describes the process model and model-based control techniques implemented on the hot blast stoves for the No. 7 Blast Furnace at the Inland Steel facility in East Chicago, Indiana. A detailed heat transfer model of the stoves is developed and verified using plant data. This model is used as part of a predictive control scheme to determine the minimum amount of fuel necessary to achieve the blast air requirements. The model is also used to predict maximum and minimum temperature constraint violations within the stove so that the controller can take corrective actions while still achieving the required stove performance.

  20. Model-based clustered-dot screening

    NASA Astrophysics Data System (ADS)

    Kim, Sang Ho

    2006-01-01

    I propose a halftone screen design method based on a human visual system model and the characteristics of the electro-photographic (EP) printer engine. Generally, screen design methods based on human visual models produce dispersed-dot type screens while design methods considering EP printer characteristics generate clustered-dot type screens. In this paper, I propose a cost function balancing the conflicting characteristics of the human visual system and the printer. By minimizing the obtained cost function, I design a model-based clustered-dot screen using a modified direct binary search algorithm. Experimental results demonstrate the superior quality of the model-based clustered-dot screen compared to a conventional clustered-dot screen.

  1. Model Based Testing for Agent Systems

    NASA Astrophysics Data System (ADS)

    Zhang, Zhiyong; Thangarajah, John; Padgham, Lin

    Although agent technology is gaining world wide popularity, a hindrance to its uptake is the lack of proper testing mechanisms for agent based systems. While many traditional software testing methods can be generalized to agent systems, there are many aspects that are different and which require an understanding of the underlying agent paradigm. In this paper we present certain aspects of a testing framework that we have developed for agent based systems. The testing framework is a model based approach using the design models of the Prometheus agent development methodology. In this paper we focus on model based unit testing and identify the appropriate units, present mechanisms for generating suitable test cases and for determining the order in which the units are to be tested, present a brief overview of the unit testing process and an example. Although we use the design artefacts from Prometheus the approach is suitable for any plan and event based agent system.

  2. A probabilistic graphical model based stochastic input model construction

    SciTech Connect

    Wan, Jiang; Zabaras, Nicholas

    2014-09-01

    Model reduction techniques have been widely used in modeling of high-dimensional stochastic input in uncertainty quantification tasks. However, the probabilistic modeling of random variables projected into reduced-order spaces presents a number of computational challenges. Due to the curse of dimensionality, the underlying dependence relationships between these random variables are difficult to capture. In this work, a probabilistic graphical model based approach is employed to learn the dependence by running a number of conditional independence tests using observation data. Thus a probabilistic model of the joint PDF is obtained and the PDF is factorized into a set of conditional distributions based on the dependence structure of the variables. The estimation of the joint PDF from data is then transformed to estimating conditional distributions under reduced dimensions. To improve the computational efficiency, a polynomial chaos expansion is further applied to represent the random field in terms of a set of standard random variables. This technique is combined with both linear and nonlinear model reduction methods. Numerical examples are presented to demonstrate the accuracy and efficiency of the probabilistic graphical model based stochastic input models. - Highlights: • Data-driven stochastic input models without the assumption of independence of the reduced random variables. • The problem is transformed to a Bayesian network structure learning problem. • Examples are given in flows in random media.

  3. Probing a GRB Progenitor at a Redshift of z=2: A Comprehensive Observing Campaign of the Afterglow of GRB 030226l

    NASA Technical Reports Server (NTRS)

    Klose, S.; Greiner, J.; Rau, A.; Henden, A. A.; Hartmann, D. H.; Zeh, A.; Ries, C.; Masetti, N.; Malesani, D.; Guenther, E.

    2004-01-01

    We report results from a comprehensive optical/near-infrared follow-up observing campaign of the afterglow of GRB 030226, including VLT spectroscopy and polarimetry, supplemented by Chandra X-ray and BOOTES-1 rapid response observations. First observations at ESO started 0.2 days after the burst when the afterglow was at a magnitude of R approx. 19. The multi-color light curve of the afterglow, with a break around 1 day after the burst, is achromatic within the observational uncertainties even during episodes of short-term fluctuations. Close to the break time the degree of linear polarization of the afterglow light was less than 1.1%, consistent with low intrinsic polarization observed in other afterglows. VLT spectra show a foreground absorber of Mg II at a redshift z=1.042 and two absorption line systems at redshifts z=1.962+/-0.001 and at z=1.986+/-0.001, placing the lower limit for the redshift of the GRB close to 2. The kinematics and the composition of the absorbing clouds is very similar to those observed in the afterglow of GRB 021004, supporting the view that at least some GRBs are physically related to the explosion of a Wolf-Rayet star.

  4. Viewing Knowledge Bases as Qualitative Models.

    ERIC Educational Resources Information Center

    Clancey, William J.

    The concept of a qualitative model provides a unifying perspective for understanding how expert systems differ from conventional programs. Knowledge bases contain qualitative models of systems in the world, that is, primarily non-numeric descriptions that provide a basis for explaining and predicting behavior and formulating action plans. The…

  5. IRT Models for Ability-Based Guessing

    ERIC Educational Resources Information Center

    Martin, Ernesto San; del Pino, Guido; De Boeck, Paul

    2006-01-01

    An ability-based guessing model is formulated and applied to several data sets regarding educational tests in language and in mathematics. The formulation of the model is such that the probability of a correct guess does not only depend on the item but also on the ability of the individual, weighted with a general discrimination parameter. By so…

  6. Mineral resources estimation based on block modeling

    NASA Astrophysics Data System (ADS)

    Bargawa, Waterman Sulistyana; Amri, Nur Ali

    2016-02-01

    The estimation in this paper uses three kinds of block models of nearest neighbor polygon, inverse distance squared and ordinary kriging. The techniques are weighting scheme which is based on the principle that block content is a linear combination of the grade data or the sample around the block being estimated. The case study in Pongkor area, here is gold-silver resource modeling that allegedly shaped of quartz vein as a hydrothermal process of epithermal type. Resources modeling includes of data entry, statistical and variography analysis of topography and geological model, the block model construction, estimation parameter, presentation model and tabulation of mineral resources. Skewed distribution, here isolated by robust semivariogram. The mineral resources classification generated in this model based on an analysis of the kriging standard deviation and number of samples which are used in the estimation of each block. Research results are used to evaluate the performance of OK and IDS estimator. Based on the visual and statistical analysis, concluded that the model of OK gives the estimation closer to the data used for modeling.

  7. Agent-Based vs. Equation-based Epidemiological Models:A Model Selection Case Study

    SciTech Connect

    Sukumar, Sreenivas R; Nutaro, James J

    2012-01-01

    This paper is motivated by the need to design model validation strategies for epidemiological disease-spread models. We consider both agent-based and equation-based models of pandemic disease spread and study the nuances and complexities one has to consider from the perspective of model validation. For this purpose, we instantiate an equation based model and an agent based model of the 1918 Spanish flu and we leverage data published in the literature for our case- study. We present our observations from the perspective of each implementation and discuss the application of model-selection criteria to compare the risk in choosing one modeling paradigm to another. We conclude with a discussion of our experience and document future ideas for a model validation framework.

  8. Evaluating model accuracy for model-based reasoning

    NASA Technical Reports Server (NTRS)

    Chien, Steve; Roden, Joseph

    1992-01-01

    Described here is an approach to automatically assessing the accuracy of various components of a model. In this approach, actual data from the operation of a target system is used to drive statistical measures to evaluate the prediction accuracy of various portions of the model. We describe how these statistical measures of model accuracy can be used in model-based reasoning for monitoring and design. We then describe the application of these techniques to the monitoring and design of the water recovery system of the Environmental Control and Life Support System (ECLSS) of Space Station Freedom.

  9. Propagation of a surface microwave along the afterglow plasma column of a high-current pulsed discharge

    SciTech Connect

    Sergeichev, K. F.; Karfidov, D. M.

    2011-09-15

    It is demonstrated experimentally that the lifetime of the afterglow plasma of a high-current pulsed discharge in a dielectric tube filled with a mixture of argon with saturated mercury vapor is longer than 1 ms. Such a long lifetime, during which the electron density decreases from 10{sup 14} to 10{sup 12} cm{sup -3}, is explained by the chemi-ionization of mercury vapor by long-lived metastable argon atoms. During this time, the afterglow plasma can serve as a microwave waveguide for a weakly damped low-noise E{sub 0}-type axisymmetric surface mode, which allows one to use it for transmission of signals in the centimeter wavelength range.

  10. The galactic model of GRBs

    SciTech Connect

    Colgate, S.A.; Li, H.

    1997-09-01

    The galactic model of gamma ray bursts (GRBs) is based upon the observed production of soft gamma ray repeaters (SGRs) in the galaxy and the consequences of a reasonable model to explain them. In this view GRBs are the long term result of the burn-out conditions of the SGRs in this and in other galaxies. A delay of {approximately} 30 million years before GRBs are being actively produced can be understood as the time required for the ejected matter during the SGR phase to cool, condense, and form planetesimals that are eventually captured by the central neutron star. The amount of disk matter and the interaction between each GRB and the disk determine the rate of burst production and turn-off time of GRBs. The x-ray afterglow as well as optical emission is derived from x-ray fluorescence and ionization of previously ablated matter.

  11. Map-based models in neuronal dynamics

    NASA Astrophysics Data System (ADS)

    Ibarz, B.; Casado, J. M.; Sanjuán, M. A. F.

    2011-04-01

    Ever since the pioneering work of Hodgkin and Huxley, biological neuron models have consisted of ODEs representing the evolution of the transmembrane voltage and the dynamics of ionic conductances. It is only recently that discrete dynamical systems-also known as maps-have begun to receive attention as valid phenomenological neuron models. The present review tries to provide a coherent perspective of map-based biological neuron models, describing their dynamical properties; stressing the similarities and differences, both among them and in relation to continuous-time models; exploring their behavior in networks; and examining their wide-ranging possibilities of application in computational neuroscience.

  12. MEGen: A Physiologically Based Pharmacokinetic Model Generator

    PubMed Central

    Loizou, George; Hogg, Alex

    2011-01-01

    Physiologically based pharmacokinetic models are being used in an increasing number of different areas. However, they are perceived as complex, data hungry, resource intensive, and time consuming. In addition, model validation and verification are hindered by the relative complexity of the equations. To begin to address these issues a web application called MEGen for the rapid construction and documentation of bespoke deterministic PBPK model code is under development. MEGen comprises a parameter database and a model code generator that produces code for use in several commercial software packages and one that is freely available. Here we present an overview of the current capabilities of MEGen, and discuss future developments. PMID:22084631

  13. [Study on self-propagating synthesis of the doped SrAl2O4 rare earth long afterglow phosphors].

    PubMed

    Li, Yuan; Zhao, Yong-Liang; Liu, Yong-Gang; Wei, Xiao-Yan; Ren, Yue

    2011-06-01

    Twenty one doped SrAl2O4 long after-glowed phosphors with 4 series were synthesized by self-propagating high-temperature synthesis method (SHS) with urea-nitrate solution which served as media at 600 degrees C. They are SrAl2O4: Eu(2+)0.012 5, RE(3+)0.012 5 (RE(3+) = Ce(3+), Pr(3+), Nd(3+), Tb(3+), Dy(3+)), SrAl2O4 : Eu(2+)0.012 5, M0.012 5 (M = Li(+), Be(2+), Cd(2+), Mn(2+), Cu(2+), Ag(+), Zn(2+), Pb(2+)), SrAl2O4 : Eu(2+)0.012 5, Dy(3+)0.012 5, M0.012 5 (M = Mn(2+), Cu(2+), Ag(+), Zn(2+)), and SrAlO4 = Eu(2+)0.012 5, Dy(3+)0.012 5, RE(3+)0.012 5 (RE(3+) = Ce(3+), Pr(3+), Nd(3+), Tb(3+)), of which luminescence and after-glowing features were tested. The morphology of all these samples presents a state of porosity and laxity. The samples show an intense emission peak at 514 nm and broad peaks of the excitation spectra at 290-360 nm, Tb(3+) and Dy(3+) had most effects on luminance and after-glowed time respectively. The SrAl2O4 : Eu(2+)0.012 5, Dy(3+)0.012 5 had good luminance and proper after-glowed time as well.

  14. Knowledge-based generalization of metabolic models.

    PubMed

    Zhukova, Anna; Sherman, David James

    2014-07-01

    Genome-scale metabolic model reconstruction is a complicated process beginning with (semi-)automatic inference of the reactions participating in the organism's metabolism, followed by many iterations of network analysis and improvement. Despite advances in automatic model inference and analysis tools, reconstruction may still miss some reactions or add erroneous ones. Consequently, a human expert's analysis of the model will continue to play an important role in all the iterations of the reconstruction process. This analysis is hampered by the size of the genome-scale models (typically thousands of reactions), which makes it hard for a human to understand them. To aid human experts in curating and analyzing metabolic models, we have developed a method for knowledge-based generalization that provides a higher-level view of a metabolic model, masking its inessential details while presenting its essential structure. The method groups biochemical species in the model into semantically equivalent classes based on the ChEBI ontology, identifies reactions that become equivalent with respect to the generalized species, and factors those reactions into generalized reactions. Generalization allows curators to quickly identify divergences from the expected structure of the model, such as alternative paths or missing reactions, that are the priority targets for further curation. We have applied our method to genome-scale yeast metabolic models and shown that it improves understanding by helping to identify both specificities and potential errors. PMID:24766276

  15. A model evaluation checklist for process-based environmental models

    NASA Astrophysics Data System (ADS)

    Jackson-Blake, Leah

    2015-04-01

    the conceptual model on which it is based. In this study, a number of model structural shortcomings were identified, such as a lack of dissolved phosphorus transport via infiltration excess overland flow, potential discrepancies in the particulate phosphorus simulation and a lack of spatial granularity. (4) Conceptual challenges, as conceptual models on which predictive models are built are often outdated, having not kept up with new insights from monitoring and experiments. For example, soil solution dissolved phosphorus concentration in INCA-P is determined by the Freundlich adsorption isotherm, which could potentially be replaced using more recently-developed adsorption models that take additional soil properties into account. This checklist could be used to assist in identifying why model performance may be poor or unreliable. By providing a model evaluation framework, it could help prioritise which areas should be targeted to improve model performance or model credibility, whether that be through using alternative calibration techniques and statistics, improved data collection, improving or simplifying the model structure or updating the model to better represent current understanding of catchment processes.

  16. EARLY X-RAY AND OPTICAL AFTERGLOW OF GRAVITATIONAL WAVE BURSTS FROM MERGERS OF BINARY NEUTRON STARS

    SciTech Connect

    Zhang Bing

    2013-01-20

    Double neutron star mergers are strong sources of gravitational waves. The upcoming advanced gravitational wave detectors are expected to make the first detection of gravitational wave bursts (GWBs) associated with these sources. Proposed electromagnetic counterparts of a GWB include a short gamma-ray burst, an optical macronova, and a long-lasting radio afterglow. Here we suggest that at least some GWBs could be followed by an early afterglow lasting for thousands of seconds, if the post-merger product is a highly magnetized, rapidly rotating, massive neutron star rather than a black hole. This afterglow is powered by dissipation of a proto-magnetar wind. The X-ray flux is estimated to be as bright as (10{sup -8}-10{sup -7}) erg s{sup -1} cm{sup -2}. The optical flux is subject to large uncertainties but could be as bright as 17th magnitude in R band. We provide observational hints of such a scenario, and discuss the challenge and strategy to detect these signals.

  17. SWIFT Discovery of Gamma-ray Bursts without Jet Break Feature in their X-ray Afterglows

    NASA Technical Reports Server (NTRS)

    Sato, G.; Yamazaki, R.; Sakamoto, T.; Takahashi, T; Nakazawa, K.; Nakamura, T.; Toma, K.; Hullinger, D.; Tashiro, M.; Parsons, A. M.; Krimm, H. A.; Barthelmy, S. D.; Gehrels, N.; Burrows, D. N.; O'Brien, P. T.; Osborne, J. P.; Chincarini, G.; Lamb, D. Q.

    2007-01-01

    We analyze Swift gamma-ray bursts (GRBs) and X-ray afterglows for three GRBs with spectroscopic redshift determinations - GRB 050401, XRF 050416a, and GRB 050525a. We find that the relation between spectral peak energy and isotropic energy of prompt emissions (the Amati relation) is consistent with that for the bursts observed in pre-Swift era. However, we find that the X-ray afterglow lightcurves, which extend up to 10 - 70 days, show no sign of the jet break that is expected in the standard framework of collimated outflows. We do so by showing that none of the X-ray afterglow lightcurves in our sample satisfies the relation between the spectral and temporal indices that is predicted for the phase after jet break. The jet break time can be predicted by inverting the tight empirical relation between the peak energy of the spectrum and the collimation-corrected energy of the prompt emission (the Ghirlanda relation). We find that there are no temporal breaks within the predicted time intervals in X-ray band. This requires either that the Ghirlanda relation has a larger scatter than previously thought, that the temporal break in X-rays is masked by some additional source of X-ray emission, or that it does not happen because of some unknown reason.

  18. Development of Ensemble Model Based Water Demand Forecasting Model

    NASA Astrophysics Data System (ADS)

    Kwon, Hyun-Han; So, Byung-Jin; Kim, Seong-Hyeon; Kim, Byung-Seop

    2014-05-01

    In recent years, Smart Water Grid (SWG) concept has globally emerged over the last decade and also gained significant recognition in South Korea. Especially, there has been growing interest in water demand forecast and optimal pump operation and this has led to various studies regarding energy saving and improvement of water supply reliability. Existing water demand forecasting models are categorized into two groups in view of modeling and predicting their behavior in time series. One is to consider embedded patterns such as seasonality, periodicity and trends, and the other one is an autoregressive model that is using short memory Markovian processes (Emmanuel et al., 2012). The main disadvantage of the abovementioned model is that there is a limit to predictability of water demands of about sub-daily scale because the system is nonlinear. In this regard, this study aims to develop a nonlinear ensemble model for hourly water demand forecasting which allow us to estimate uncertainties across different model classes. The proposed model is consist of two parts. One is a multi-model scheme that is based on combination of independent prediction model. The other one is a cross validation scheme named Bagging approach introduced by Brieman (1996) to derive weighting factors corresponding to individual models. Individual forecasting models that used in this study are linear regression analysis model, polynomial regression, multivariate adaptive regression splines(MARS), SVM(support vector machine). The concepts are demonstrated through application to observed from water plant at several locations in the South Korea. Keywords: water demand, non-linear model, the ensemble forecasting model, uncertainty. Acknowledgements This subject is supported by Korea Ministry of Environment as "Projects for Developing Eco-Innovation Technologies (GT-11-G-02-001-6)

  19. Physiologically based models of metal kinetics.

    PubMed

    O'Flaherty, E J

    1998-05-01

    The issues confronting the modeler of metals kinetics are somewhat different from those with which the modeler of organic chemical behavior is faced. Particularly important features of metals kinetics include metal-protein binding and metal-metal interactions. Reduction, and for some metals oxidation, is frequently an intrinsic part of metal metabolism. Alkylation/dealkylation reactions may or may not render the metal less active, and the behavior of alkylated or dealkylated metabolites must often be included in a complete kinetic model. Despite these complexities, the kinetics of metals are as amenable to the techniques of physiologically based modeling as are the kinetics of organic chemicals. Like all models, those for metals kinetics have the potential to organize a variety of observations, sometimes including apparently inconsistent observations, into a coherent framework of behavior, to identify needs for more complete experimental information, and to assist the risk assessor in making judgments concerning dose-response relationships. Development of physiologically based models of the kinetic behavior of metals is in its very early stages. The kinetics of only four metals, arsenic, chromium, mercury, and lead, have been modeled with any degree of completeness. Of these, the lead model is the most fully realized at the present time. The chromium and mercury models are still in the process of development, and experimental data are being gathered to support further development and refinement of the arsenic model. We may expect to see continued progress made on these models and their practical applications, as well as the development of new models for other toxicologically significant metals such as cadmium, manganese, nickel, and aluminum. PMID:9631283

  20. Binaural processing model based on contralateral inhibition. I. Model structure.

    PubMed

    Breebaart, J; van de Par, S; Kohlrausch, A

    2001-08-01

    This article presents a quantitative binaural signal detection model which extends the monaural model described by Dau et al. [J. Acoust. Soc. Am. 99, 3615-3622 (1996)]. The model is divided into three stages. The first stage comprises peripheral preprocessing in the right and left monaural channels. The second stage is a binaural processor which produces a time-dependent internal representation of the binaurally presented stimuli. This stage is based on the Jeffress delay line extended with tapped attenuator lines. Through this extension, the internal representation codes both interaural time and intensity differences. In contrast to most present-day models, which are based on excitatory-excitatory interaction, the binaural interaction in the present model is based on contralateral inhibition of ipsilateral signals. The last stage, a central processor, extracts a decision variable that can be used to detect the presence of a signal in a detection task, but could also derive information about the position and the compactness of a sound source. In two accompanying articles, the model predictions are compared with data obtained with human observers in a great variety of experimental conditions. PMID:11519576

  1. Atom-Role-Based Access Control Model

    NASA Astrophysics Data System (ADS)

    Cai, Weihong; Huang, Richeng; Hou, Xiaoli; Wei, Gang; Xiao, Shui; Chen, Yindong

    Role-based access control (RBAC) model has been widely recognized as an efficient access control model and becomes a hot research topic of information security at present. However, in the large-scale enterprise application environments, the traditional RBAC model based on the role hierarchy has the following deficiencies: Firstly, it is unable to reflect the role relationships in complicated cases effectively, which does not accord with practical applications. Secondly, the senior role unconditionally inherits all permissions of the junior role, thus if a user is under the supervisor role, he may accumulate all permissions, and this easily causes the abuse of permission and violates the least privilege principle, which is one of the main security principles. To deal with these problems, we, after analyzing permission types and role relationships, proposed the concept of atom role and built an atom-role-based access control model, called ATRBAC, by dividing the permission set of each regular role based on inheritance path relationships. Through the application-specific analysis, this model can well meet the access control requirements.

  2. Evolutionary modeling-based approach for model errors correction

    NASA Astrophysics Data System (ADS)

    Wan, S. Q.; He, W. P.; Wang, L.; Jiang, W.; Zhang, W.

    2012-08-01

    The inverse problem of using the information of historical data to estimate model errors is one of the science frontier research topics. In this study, we investigate such a problem using the classic Lorenz (1963) equation as a prediction model and the Lorenz equation with a periodic evolutionary function as an accurate representation of reality to generate "observational data." On the basis of the intelligent features of evolutionary modeling (EM), including self-organization, self-adaptive and self-learning, the dynamic information contained in the historical data can be identified and extracted by computer automatically. Thereby, a new approach is proposed to estimate model errors based on EM in the present paper. Numerical tests demonstrate the ability of the new approach to correct model structural errors. In fact, it can actualize the combination of the statistics and dynamics to certain extent.

  3. Predictor-Based Model Reference Adaptive Control

    NASA Technical Reports Server (NTRS)

    Lavretsky, Eugene; Gadient, Ross; Gregory, Irene M.

    2009-01-01

    This paper is devoted to robust, Predictor-based Model Reference Adaptive Control (PMRAC) design. The proposed adaptive system is compared with the now-classical Model Reference Adaptive Control (MRAC) architecture. Simulation examples are presented. Numerical evidence indicates that the proposed PMRAC tracking architecture has better than MRAC transient characteristics. In this paper, we presented a state-predictor based direct adaptive tracking design methodology for multi-input dynamical systems, with partially known dynamics. Efficiency of the design was demonstrated using short period dynamics of an aircraft. Formal proof of the reported PMRAC benefits constitute future research and will be reported elsewhere.

  4. SWIFT MODELLER: a Java based GUI for molecular modeling.

    PubMed

    Mathur, Abhinav; Shankaracharya; Vidyarthi, Ambarish S

    2011-10-01

    MODELLER is command line argument based software which requires tedious formatting of inputs and writing of Python scripts which most people are not comfortable with. Also the visualization of output becomes cumbersome due to verbose files. This makes the whole software protocol very complex and requires extensive study of MODELLER manuals and tutorials. Here we describe SWIFT MODELLER, a GUI that automates formatting, scripting and data extraction processes and present it in an interactive way making MODELLER much easier to use than before. The screens in SWIFT MODELLER are designed keeping homology modeling in mind and their flow is a depiction of its steps. It eliminates the formatting of inputs, scripting processes and analysis of verbose output files through automation and makes pasting of the target sequence as the only prerequisite. Jmol (3D structure visualization tool) has been integrated into the GUI which opens and demonstrates the protein data bank files created by the MODELLER software. All files required and created by the software are saved in a folder named after the work instance's date and time of execution. SWIFT MODELLER lowers the skill level required for the software through automation of many of the steps in the original software protocol, thus saving an enormous amount of time per instance and making MODELLER very easy to work with.

  5. A late-time flattening of light curves in gamma-ray burst afterglows

    SciTech Connect

    Sironi, Lorenzo; Giannios, Dimitrios E-mail: dgiannio@purdue.edu

    2013-12-01

    The afterglow emission from gamma-ray bursts (GRBs) is usually interpreted as synchrotron radiation from relativistic electrons accelerated at the GRB external shock. We investigate the temporal decay of the afterglow emission at late times, when the bulk of the shock-accelerated electrons are non-relativistic (the 'deep Newtonian phase', as denoted by Huang and Cheng). We assume that the electron spectrum in the deep Newtonian phase is a power-law distribution in momentum with slope p, as dictated by the theory of Fermi acceleration in non-relativistic shocks. For a uniform circumburst medium, the deep Newtonian phase begins at t{sub DN}∼3 ϵ{sub e,−1}{sup 5/6}t{sub ST}, where t {sub ST} marks the transition of the blast wave to the non-relativistic, spherically symmetric Sedov-Taylor (ST) solution, and ε {sub e} = 0.1 ε {sub e,–1} quantifies the amount of shock energy transferred to the electrons. For typical parameters, the deep Newtonian stage starts ∼0.5 to several years after the GRB. The radio flux in this phase decays as F {sub ν}∝t {sup –3(p+1)/10}∝t {sup –(0.9÷1.2)}, for a power-law slope 2 < p < 3. This is shallower than the scaling F {sub ν}∝t {sup –3(5p–7)/10}∝t {sup –(0.9÷2.4)} derived by Frail et al., which only applies if the GRB shock is non-relativistic, but the electron distribution still peaks at ultra-relativistic energies (a regime that is relevant for a narrow time interval, and only if t {sub DN} ≳ t {sub ST}, namely, ε {sub e} ≳ 0.03). We discuss how the deep Newtonian phase can be reliably used for GRB calorimetry, and we comment on the good detection prospects of trans-relativistic blast waves at 0.1÷10 GHz with the Karl G. Jansky Very Large Array and LOw-Frequency ARray.

  6. LUMINOSITY CORRELATIONS FOR GAMMA-RAY BURSTS AND IMPLICATIONS FOR THEIR PROMPT AND AFTERGLOW EMISSION MECHANISMS

    SciTech Connect

    Sultana, J.; Kazanas, D.; Fukumura, K.

    2012-10-10

    We present the relation between the (z- and k-corrected) spectral lags, {tau}, for the standard Swift energy bands 50-100 keV and 100-200 keV and the peak isotropic luminosity, L{sub iso} (a relation reported first by Norris et al.), for a subset of 12 long Swift gamma-ray bursts (GRBs) taken from a recent study of this relation by Ukwatta et al. The chosen GRBs are also a subset of the Dainotti et al. sample, a set of Swift GRBs of known redshift, employed in establishing a relation between the (GRB frame) luminosity, L{sub X} , of the shallow (or constant) flux portion of the typical X-Ray Telescope GRB-afterglow light curve and the (GRB frame) time of transition to the normal decay rate, T{sub brk}. We also present the L{sub X} -T{sub brk} relation using only the bursts common in the two samples. The two relations exhibit a significant degree of correlation ({rho} = -0.65 for the L{sub iso}-{tau} and {rho} = -0.88 for the L{sub X} -T{sub brk} relation) and have surprisingly similar best-fit power-law indices (-1.19 {+-} 0.17 for L{sub iso}-{tau} and -1.10 {+-} 0.03 for L{sub X} -T{sub brk}). Even more surprisingly, we noted that although {tau} and T{sub brk} represent different GRB time variables, it appears that the first relation (L{sub iso}-{tau}) extrapolates into the second one for timescales {tau} {approx_equal} T{sub brk}. This fact suggests that these two relations have a common origin, which we conjecture to be kinematic. This relation adds to the recently discovered relations between properties of the prompt and afterglow GRB phases, indicating a much more intimate relation between these two phases than hitherto considered.

  7. A Late-time Flattening of Light Curves in Gamma-Ray Burst Afterglows

    NASA Astrophysics Data System (ADS)

    Sironi, Lorenzo; Giannios, Dimitrios

    2013-12-01

    The afterglow emission from gamma-ray bursts (GRBs) is usually interpreted as synchrotron radiation from relativistic electrons accelerated at the GRB external shock. We investigate the temporal decay of the afterglow emission at late times, when the bulk of the shock-accelerated electrons are non-relativistic (the "deep Newtonian phase," as denoted by Huang and Cheng). We assume that the electron spectrum in the deep Newtonian phase is a power-law distribution in momentum with slope p, as dictated by the theory of Fermi acceleration in non-relativistic shocks. For a uniform circumburst medium, the deep Newtonian phase begins at t{_{\\scriptsize {DN}}}\\sim 3\\,\\epsilon _{e,-1}^{5/6}t{_{\\scriptsize {ST}}}, where t ST marks the transition of the blast wave to the non-relativistic, spherically symmetric Sedov-Taylor (ST) solution, and epsilon e = 0.1 epsilon e, -1 quantifies the amount of shock energy transferred to the electrons. For typical parameters, the deep Newtonian stage starts ~0.5 to several years after the GRB. The radio flux in this phase decays as F νvpropt -3(p + 1)/10vpropt -(0.9÷1.2), for a power-law slope 2 < p < 3. This is shallower than the scaling F νvpropt -3(5p - 7)/10vpropt -(0.9÷2.4) derived by Frail et al., which only applies if the GRB shock is non-relativistic, but the electron distribution still peaks at ultra-relativistic energies (a regime that is relevant for a narrow time interval, and only if t DN >~ t ST, namely, epsilon e >~ 0.03). We discuss how the deep Newtonian phase can be reliably used for GRB calorimetry, and we comment on the good detection prospects of trans-relativistic blast waves at 0.1÷10 GHz with the Karl G. Jansky Very Large Array and LOw-Frequency ARray.

  8. Entropy-based portfolio models: Practical issues

    NASA Astrophysics Data System (ADS)

    Shirazi, Yasaman Izadparast; Sabiruzzaman, Md.; Hamzah, Nor Aishah

    2015-10-01

    Entropy is a nonparametric alternative of variance and has been used as a measure of risk in portfolio analysis. In this paper, the computation of entropy risk for a given set of data is discussed with illustration. A comparison between entropy-based portfolio models is made. We propose a natural extension of the mean entropy portfolio to make it more general and diversified. In terms of performance, this new model is similar to the mean-entropy portfolio when applied to real and simulated data, and offers higher return if no constraint is set for the desired return; also it is found to be the most diversified portfolio model.

  9. A subgrid based approach for morphodynamic modelling

    NASA Astrophysics Data System (ADS)

    Volp, N. D.; van Prooijen, B. C.; Pietrzak, J. D.; Stelling, G. S.

    2016-07-01

    To improve the accuracy and the efficiency of morphodynamic simulations, we present a subgrid based approach for a morphodynamic model. This approach is well suited for areas characterized by sub-critical flow, like in estuaries, coastal areas and in low land rivers. This new method uses a different grid resolution to compute the hydrodynamics and the morphodynamics. The hydrodynamic computations are carried out with a subgrid based, two-dimensional, depth-averaged model. This model uses a coarse computational grid in combination with a subgrid. The subgrid contains high resolution bathymetry and roughness information to compute volumes, friction and advection. The morphodynamic computations are carried out entirely on a high resolution grid, the bed grid. It is key to find a link between the information defined on the different grids in order to guaranty the feedback between the hydrodynamics and the morphodynamics. This link is made by using a new physics-based interpolation method. The method interpolates water levels and velocities from the coarse grid to the high resolution bed grid. The morphodynamic solution improves significantly when using the subgrid based method compared to a full coarse grid approach. The Exner equation is discretised with an upwind method based on the direction of the bed celerity. This ensures a stable solution for the Exner equation. By means of three examples, it is shown that the subgrid based approach offers a significant improvement at a minimal computational cost.

  10. Modeling Web-Based Educational Systems: Process Design Teaching Model

    ERIC Educational Resources Information Center

    Rokou, Franca Pantano; Rokou, Elena; Rokos, Yannis

    2004-01-01

    Using modeling languages is essential to the construction of educational systems based on software engineering principles and methods. Furthermore, the instructional design is undoubtedly the cornerstone of the design and development of educational systems. Although several methodologies and languages have been proposed for the specification of…

  11. Incident duration modeling using flexible parametric hazard-based models.

    PubMed

    Li, Ruimin; Shang, Pan

    2014-01-01

    Assessing and prioritizing the duration time and effects of traffic incidents on major roads present significant challenges for road network managers. This study examines the effect of numerous factors associated with various types of incidents on their duration and proposes an incident duration prediction model. Several parametric accelerated failure time hazard-based models were examined, including Weibull, log-logistic, log-normal, and generalized gamma, as well as all models with gamma heterogeneity and flexible parametric hazard-based models with freedom ranging from one to ten, by analyzing a traffic incident dataset obtained from the Incident Reporting and Dispatching System in Beijing in 2008. Results show that different factors significantly affect different incident time phases, whose best distributions were diverse. Given the best hazard-based models of each incident time phase, the prediction result can be reasonable for most incidents. The results of this study can aid traffic incident management agencies not only in implementing strategies that would reduce incident duration, and thus reduce congestion, secondary incidents, and the associated human and economic losses, but also in effectively predicting incident duration time.

  12. Incident duration modeling using flexible parametric hazard-based models.

    PubMed

    Li, Ruimin; Shang, Pan

    2014-01-01

    Assessing and prioritizing the duration time and effects of traffic incidents on major roads present significant challenges for road network managers. This study examines the effect of numerous factors associated with various types of incidents on their duration and proposes an incident duration prediction model. Several parametric accelerated failure time hazard-based models were examined, including Weibull, log-logistic, log-normal, and generalized gamma, as well as all models with gamma heterogeneity and flexible parametric hazard-based models with freedom ranging from one to ten, by analyzing a traffic incident dataset obtained from the Incident Reporting and Dispatching System in Beijing in 2008. Results show that different factors significantly affect different incident time phases, whose best distributions were diverse. Given the best hazard-based models of each incident time phase, the prediction result can be reasonable for most incidents. The results of this study can aid traffic incident management agencies not only in implementing strategies that would reduce incident duration, and thus reduce congestion, secondary incidents, and the associated human and economic losses, but also in effectively predicting incident duration time. PMID:25530753

  13. Haptics-based dynamic implicit solid modeling.

    PubMed

    Hua, Jing; Qin, Hong

    2004-01-01

    This paper systematically presents a novel, interactive solid modeling framework, Haptics-based Dynamic Implicit Solid Modeling, which is founded upon volumetric implicit functions and powerful physics-based modeling. In particular, we augment our modeling framework with a haptic mechanism in order to take advantage of additional realism associated with a 3D haptic interface. Our dynamic implicit solids are semi-algebraic sets of volumetric implicit functions and are governed by the principles of dynamics, hence responding to sculpting forces in a natural and predictable manner. In order to directly manipulate existing volumetric data sets as well as point clouds, we develop a hierarchical fitting algorithm to reconstruct and represent discrete data sets using our continuous implicit functions, which permit users to further design and edit those existing 3D models in real-time using a large variety of haptic and geometric toolkits, and visualize their interactive deformation at arbitrary resolution. The additional geometric and physical constraints afford more sophisticated control of the dynamic implicit solids. The versatility of our dynamic implicit modeling enables the user to easily modify both the geometry and the topology of modeled objects, while the inherent physical properties can offer an intuitive haptic interface for direct manipulation with force feedback.

  14. Indiana Distributive Education Competency Based Model.

    ERIC Educational Resources Information Center

    Davis, Rod; And Others

    This Indiana distributive education competency-based curriculum model is designed to help teachers and local administrators plan and conduct a comprehensive marketing and distributive education program. It is divided into three levels--one level for each year of a three-year program. The competencies common to a variety of marketing and…

  15. Sandboxes for Model-Based Inquiry

    ERIC Educational Resources Information Center

    Brady, Corey; Holbert, Nathan; Soylu, Firat; Novak, Michael; Wilensky, Uri

    2015-01-01

    In this article, we introduce a class of constructionist learning environments that we call "Emergent Systems Sandboxes" ("ESSs"), which have served as a centerpiece of our recent work in developing curriculum to support scalable model-based learning in classroom settings. ESSs are a carefully specified form of virtual…

  16. Model-Based Inquiries in Chemistry

    ERIC Educational Resources Information Center

    Khan, Samia

    2007-01-01

    In this paper, instructional strategies for sustaining model-based inquiry in an undergraduate chemistry class were analyzed through data collected from classroom observations, a student survey, and in-depth problem-solving sessions with the instructor and students. Analysis of teacher-student interactions revealed a cyclical pattern in which…

  17. Gamma-Ray Burst Afterglows as Probes of Environment and Blast Wave Physics. II. The Distribution of rho and Structure of the Circumburst Medium

    NASA Technical Reports Server (NTRS)

    Starling, R. L. C.; vanderHorst, A. J.; Rol, E.; Wijers, R. A. M. J.; Kouveliotou, C.; Wiersema, K.; Curran, P. A.; Weltervrede, P.

    2008-01-01

    We constrain blast wave parameters and the circumburst media ofa subsample of 10 BeppoSAX gamma-ray bursts (GRBs). For this sample we derive the values of the injected electron energy distribution index, p, and the density structure index of the circumburst medium, k, from simultaneous spectral fits to their X-ray, optical, and NIR afterglow data. The spectral fits have been done in count space and include the effects ofmetallicity, and are compared with the previously reported optical and X-ray temporal behavior. Using the blast wave model and some assumptions which include on-axis viewing and standard jet structure, constant blast wave energy, and no evolution of the microphysical parameters, we find a mean value ofp for the sample as a whole of 9.... oa -0.003.0" 2 a_ statistical analysis of the distribution demonstrates that the p-values in this sample are inconsistent with a single universal value forp at the 3 _ level or greater, which has significant implications for particle acceleration models. This approach provides us with a measured distribution ofcircumburst density structures rather than considering only the cases of k ----0 (homogeneous) and k - 2 (windlike). We find five GRBs for which k can be well constrained, and in four of these cases the circumburst medium is clearly windlike. The fifth source has a value of 0 < k < 1, consistent with a homogeneous circumburst medium.

  18. Real-time analysis of ambient organic aerosols using aerosol flowing atmospheric-pressure afterglow mass spectrometry (AeroFAPA-MS)

    NASA Astrophysics Data System (ADS)

    Brüggemann, Martin; Karu, Einar; Stelzer, Torsten; Hoffmann, Thorsten

    2015-04-01

    Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, in press. 2) Shelley, J. T.; Wiley, J. S.; Hieftje, G. M. Ultrasensitive Ambient Mass Spectrometric Analysis with a Pin-to-Capillary Flowing Atmospheric-Pressure Afterglow Source. Anal. Chem. 2011, 83(14), 5741-5748; DOI 10.1021/Ac201053q. 3) Albert, A.; Shelley, J.; Engelhard, C. Plasma-based ambient desorption/ionization mass spectrometry: state-of-the-art in qualitative and quantitative analysis. Anal Bioanal Chem 2014, 406(25), 6111-6127; DOI 10.1007/s00216-014-7989-z.

  19. Unifying Model-Based and Reactive Programming within a Model-Based Executive

    NASA Technical Reports Server (NTRS)

    Williams, Brian C.; Gupta, Vineet; Norvig, Peter (Technical Monitor)

    1999-01-01

    Real-time, model-based, deduction has recently emerged as a vital component in AI's tool box for developing highly autonomous reactive systems. Yet one of the current hurdles towards developing model-based reactive systems is the number of methods simultaneously employed, and their corresponding melange of programming and modeling languages. This paper offers an important step towards unification. We introduce RMPL, a rich modeling language that combines probabilistic, constraint-based modeling with reactive programming constructs, while offering a simple semantics in terms of hidden state Markov processes. We introduce probabilistic, hierarchical constraint automata (PHCA), which allow Markov processes to be expressed in a compact representation that preserves the modularity of RMPL programs. Finally, a model-based executive, called Reactive Burton is described that exploits this compact encoding to perform efficIent simulation, belief state update and control sequence generation.

  20. A COMPREHENSIVE STUDY OF GAMMA-RAY BURST OPTICAL EMISSION. II. AFTERGLOW ONSET AND LATE RE-BRIGHTENING COMPONENTS

    SciTech Connect

    Liang Enwei; Li Liang; Liang Yunfeng; Tang Qingwen; Chen Jiemin; Lu Ruijing; Lue Lianzhong; Gao He; Zhang, Bing; Lue Houjun; Wu Xuefeng; Yi Shuangxi; Dai Zigao; Zhang Jin; Wei Jianyan E-mail: zhang@physics.unlv.edu

    2013-09-01

    We continue our systematic statistical study of various components of gamma-ray burst (GRB) optical light curves. We decompose the early onset bump and the late re-brightening bump with empirical fits and analyze their statistical properties. Among the 146 GRBs that have well-sampled optical light curves, the onset and re-brightening bumps are observed in 38 and 26 GRBs, respectively. It is found that the typical rising and decaying slopes for both the onset and re-brightening bumps are {approx}1.5 and {approx} - 1.15, respectively. No early onset bumps in the X-ray band are detected to be associated with the optical onset bumps, while an X-ray re-brightening bump is detected for half of the re-brightening optical bumps. The peak luminosity is anti-correlated with the peak time L{sub p}{proportional_to}t{sub p}{sup -1.81{+-}0.32} for the onset bumps and L{sub p}{proportional_to}t{sub p}{sup -0.83{+-}0.17} for the re-brightening bumps. Both L{sub p} and the isotropic energy release of the onset bumps are correlated with E{sub {gamma},iso}, whereas no similar correlation is found for the re-brightening bumps. These results suggest that the afterglow onset bumps are likely due to the deceleration of the GRB fireballs. Taking the onset bumps as probes for the properties of the fireballs and their ambient medium, we find that the typical power-law index of the relativistic electrons is 2.5 and the medium density profile behaves as n{proportional_to}r {sup -1} within the framework of the synchrotron external shock models. With the medium density profile obtained from our analysis, we also confirm the correlation between the initial Lorentz factor ({Gamma}{sub 0}) and E{sub iso,{gamma}} in our previous work. The jet component that produces the re-brightening bump seems to be on-axis and independent of the prompt emission jet component. Its typical kinetic energy budget would be about one order of magnitude larger than the prompt emission component, but with a lower {Gamma

  1. Agent Based Modeling as an Educational Tool

    NASA Astrophysics Data System (ADS)

    Fuller, J. H.; Johnson, R.; Castillo, V.

    2012-12-01

    Motivation is a key element in high school education. One way to improve motivation and provide content, while helping address critical thinking and problem solving skills, is to have students build and study agent based models in the classroom. This activity visually connects concepts with their applied mathematical representation. "Engaging students in constructing models may provide a bridge between frequently disconnected conceptual and mathematical forms of knowledge." (Levy and Wilensky, 2011) We wanted to discover the feasibility of implementing a model based curriculum in the classroom given current and anticipated core and content standards.; Simulation using California GIS data ; Simulation of high school student lunch popularity using aerial photograph on top of terrain value map.

  2. Simulations of Gamma-Ray Burst Jets in a Stratified External Medium: Dynamics, Afterglow Light Curves, Jet Breaks, and Radio Calorimetry

    NASA Astrophysics Data System (ADS)

    De Colle, Fabio; Ramirez-Ruiz, Enrico; Granot, Jonathan; Lopez-Camara, Diego

    2012-05-01

    The dynamics of gamma-ray burst (GRB) jets during the afterglow phase is most reliably and accurately modeled using hydrodynamic simulations. All published simulations so far, however, have considered only a uniform external medium, while a stratified external medium is expected around long duration GRB progenitors. Here, we present simulations of the dynamics of GRB jets and the resulting afterglow emission for both uniform and stratified external media with ρextvpropr -k for k = 0, 1, 2. The simulations are performed in two dimensions using the special relativistic version of the Mezcal code. Common to all calculations is the initiation of the GRB jet as a conical wedge of half-opening angle θ0 = 0.2 whose radial profile is taken from the self-similar Blandford-McKee solution. The dynamics for stratified external media (k = 1, 2) are broadly similar to those derived for expansion into a uniform external medium (k = 0). The jet half-opening angle is observed to start increasing logarithmically with time (or radius) once the Lorentz factor Γ drops below θ-1 0. For larger k values, however, the lateral expansion is faster at early times (when Γ > θ-1 0) and slower at late times with the jet expansion becoming Newtonian and slowly approaching spherical symmetry over progressively longer timescales. We find that, contrary to analytic expectations, there is a reasonably sharp jet break in the light curve for k = 2 (a wind-like external medium), although the shape of the break is affected more by the viewing angle (for θobs <= θ0) than by the slope of the external density profile (for 0 <= k <= 2). Steeper density profiles (i.e., increasing k values) are found to produce more gradual jet breaks while larger viewing angles cause smoother and later appearing jet breaks. The counterjet becomes visible as it becomes sub-relativistic, and for k = 0 this results in a clear bump-like feature in the light curve. However, for larger k values the jet decelerates more

  3. Entropy Based Modelling for Estimating Demographic Trends.

    PubMed

    Li, Guoqi; Zhao, Daxuan; Xu, Yi; Kuo, Shyh-Hao; Xu, Hai-Yan; Hu, Nan; Zhao, Guangshe; Monterola, Christopher

    2015-01-01

    In this paper, an entropy-based method is proposed to forecast the demographical changes of countries. We formulate the estimation of future demographical profiles as a constrained optimization problem, anchored on the empirically validated assumption that the entropy of age distribution is increasing in time. The procedure of the proposed method involves three stages, namely: 1) Prediction of the age distribution of a country's population based on an "age-structured population model"; 2) Estimation the age distribution of each individual household size with an entropy-based formulation based on an "individual household size model"; and 3) Estimation the number of each household size based on a "total household size model". The last stage is achieved by projecting the age distribution of the country's population (obtained in stage 1) onto the age distributions of individual household sizes (obtained in stage 2). The effectiveness of the proposed method is demonstrated by feeding real world data, and it is general and versatile enough to be extended to other time dependent demographic variables. PMID:26382594

  4. Intelligent-based Structural Damage Detection Model

    SciTech Connect

    Lee, Eric Wai Ming; Yu, K.F.

    2010-05-21

    This paper presents the application of a novel Artificial Neural Network (ANN) model for the diagnosis of structural damage. The ANN model, denoted as the GRNNFA, is a hybrid model combining the General Regression Neural Network Model (GRNN) and the Fuzzy ART (FA) model. It not only retains the important features of the GRNN and FA models (i.e. fast and stable network training and incremental growth of network structure) but also facilitates the removal of the noise embedded in the training samples. Structural damage alters the stiffness distribution of the structure and so as to change the natural frequencies and mode shapes of the system. The measured modal parameter changes due to a particular damage are treated as patterns for that damage. The proposed GRNNFA model was trained to learn those patterns in order to detect the possible damage location of the structure. Simulated data is employed to verify and illustrate the procedures of the proposed ANN-based damage diagnosis methodology. The results of this study have demonstrated the feasibility of applying the GRNNFA model to structural damage diagnosis even when the training samples were noise contaminated.

  5. [Fast spectral modeling based on Voigt peaks].

    PubMed

    Li, Jin-rong; Dai, Lian-kui

    2012-03-01

    Indirect hard modeling (IHM) is a recently introduced method for quantitative spectral analysis, which was applied to the analysis of nonlinear relation between mixture spectrum and component concentration. In addition, IHM is an effectual technology for the analysis of components of mixture with molecular interactions and strongly overlapping bands. Before the establishment of regression model, IHM needs to model the measured spectrum as a sum of Voigt peaks. The precision of the spectral model has immediate impact on the accuracy of the regression model. A spectrum often includes dozens or even hundreds of Voigt peaks, which mean that spectral modeling is a optimization problem with high dimensionality in fact. So, large operation overhead is needed and the solution would not be numerically unique due to the ill-condition of the optimization problem. An improved spectral modeling method is presented in the present paper, which reduces the dimensionality of optimization problem by determining the overlapped peaks in spectrum. Experimental results show that the spectral modeling based on the new method is more accurate and needs much shorter running time than conventional method. PMID:22582612

  6. Intelligent-based Structural Damage Detection Model

    NASA Astrophysics Data System (ADS)

    Lee, Eric Wai Ming; Yu, Kin Fung

    2010-05-01

    This paper presents the application of a novel Artificial Neural Network (ANN) model for the diagnosis of structural damage. The ANN model, denoted as the GRNNFA, is a hybrid model combining the General Regression Neural Network Model (GRNN) and the Fuzzy ART (FA) model. It not only retains the important features of the GRNN and FA models (i.e. fast and stable network training and incremental growth of network structure) but also facilitates the removal of the noise embedded in the training samples. Structural damage alters the stiffness distribution of the structure and so as to change the natural frequencies and mode shapes of the system. The measured modal parameter changes due to a particular damage are treated as patterns for that damage. The proposed GRNNFA model was trained to learn those patterns in order to detect the possible damage location of the structure. Simulated data is employed to verify and illustrate the procedures of the proposed ANN-based damage diagnosis methodology. The results of this study have demonstrated the feasibility of applying the GRNNFA model to structural damage diagnosis even when the training samples were noise contaminated.

  7. Stochastic modelling of evaporation based on copulas

    NASA Astrophysics Data System (ADS)

    Pham, Minh Tu; Vernieuwe, Hilde; De Baets, Bernard; Verhoest, Niko

    2015-04-01

    Evapotranspiration is an important process in the water cycle that represents a considerable amount of moisture lost through evaporation from the soil surface and transpiration from plants in a watershed. Therefore, an accurate estimate of evapotranspiration rates is necessary, along with precipitation data, for running hydrological models. Often, daily reference evapotranspiration is modelled based on the Penman, Priestley-Taylor or Hargraeves equation. However, each of these models requires extensive input data, such as daily mean temperature, wind speed, relative humidity and solar radiation. Yet, in design studies, such data is unavailable in case stochastically generated time series of precipitation are used to force a hydrologic model. In the latter case, an alternative model approach is needed that allows for generating evapotranspiration data that are consistent with the accompanying precipitation data. This contribution presents such an approach in which the statistical dependence between evapotranspiration, temperature and precipitation is described by three- and four-dimensional vine copulas. Based on a case study of 72 years of evapotranspiration, temperature and precipitation data, observed in Uccle, Belgium, it was found that canonical vine copulas (C-Vines) in which bivariate Frank copulas are employed perform very well in preserving the dependencies between variables. While 4-dimensional C-Vine copulas performed best in simulating time series of evapotranspiration, a 3-dimensional C-Vine copula (relating evapotranspiration, daily precipitation depth and temperature) still allows for modelling evapotranspiration, though with larger error statistics.

  8. Sandboxes for Model-Based Inquiry

    NASA Astrophysics Data System (ADS)

    Brady, Corey; Holbert, Nathan; Soylu, Firat; Novak, Michael; Wilensky, Uri

    2015-04-01

    In this article, we introduce a class of constructionist learning environments that we call Emergent Systems Sandboxes ( ESSs), which have served as a centerpiece of our recent work in developing curriculum to support scalable model-based learning in classroom settings. ESSs are a carefully specified form of virtual construction environment that support students in creating, exploring, and sharing computational models of dynamic systems that exhibit emergent phenomena. They provide learners with "entity"-level construction primitives that reflect an underlying scientific model. These primitives can be directly "painted" into a sandbox space, where they can then be combined, arranged, and manipulated to construct complex systems and explore the emergent properties of those systems. We argue that ESSs offer a means of addressing some of the key barriers to adopting rich, constructionist model-based inquiry approaches in science classrooms at scale. Situating the ESS in a large-scale science modeling curriculum we are implementing across the USA, we describe how the unique "entity-level" primitive design of an ESS facilitates knowledge system refinement at both an individual and social level, we describe how it supports flexible modeling practices by providing both continuous and discrete modes of executability, and we illustrate how it offers students a variety of opportunities for validating their qualitative understandings of emergent systems as they develop.

  9. Efficient Model-Based Diagnosis Engine

    NASA Technical Reports Server (NTRS)

    Fijany, Amir; Vatan, Farrokh; Barrett, Anthony; James, Mark; Mackey, Ryan; Williams, Colin

    2009-01-01

    An efficient diagnosis engine - a combination of mathematical models and algorithms - has been developed for identifying faulty components in a possibly complex engineering system. This model-based diagnosis engine embodies a twofold approach to reducing, relative to prior model-based diagnosis engines, the amount of computation needed to perform a thorough, accurate diagnosis. The first part of the approach involves a reconstruction of the general diagnostic engine to reduce the complexity of the mathematical-model calculations and of the software needed to perform them. The second part of the approach involves algorithms for computing a minimal diagnosis (the term "minimal diagnosis" is defined below). A somewhat lengthy background discussion is prerequisite to a meaningful summary of the innovative aspects of the present efficient model-based diagnosis engine. In model-based diagnosis, the function of each component and the relationships among all the components of the engineering system to be diagnosed are represented as a logical system denoted the system description (SD). Hence, the expected normal behavior of the engineering system is the set of logical consequences of the SD. Faulty components lead to inconsistencies between the observed behaviors of the system and the SD (see figure). Diagnosis - the task of finding faulty components - is reduced to finding those components, the abnormalities of which could explain all the inconsistencies. The solution of the diagnosis problem should be a minimal diagnosis, which is a minimal set of faulty components. A minimal diagnosis stands in contradistinction to the trivial solution, in which all components are deemed to be faulty, and which, therefore, always explains all inconsistencies.

  10. Satellite-based terrestrial production efficiency modeling

    PubMed Central

    McCallum, Ian; Wagner, Wolfgang; Schmullius, Christiane; Shvidenko, Anatoly; Obersteiner, Michael; Fritz, Steffen; Nilsson, Sten

    2009-01-01

    Production efficiency models (PEMs) are based on the theory of light use efficiency (LUE) which states that a relatively constant relationship exists between photosynthetic carbon uptake and radiation receipt at the canopy level. Challenges remain however in the application of the PEM methodology to global net primary productivity (NPP) monitoring. The objectives of this review are as follows: 1) to describe the general functioning of six PEMs (CASA; GLO-PEM; TURC; C-Fix; MOD17; and BEAMS) identified in the literature; 2) to review each model to determine potential improvements to the general PEM methodology; 3) to review the related literature on satellite-based gross primary productivity (GPP) and NPP modeling for additional possibilities for improvement; and 4) based on this review, propose items for coordinated research. This review noted a number of possibilities for improvement to the general PEM architecture - ranging from LUE to meteorological and satellite-based inputs. Current PEMs tend to treat the globe similarly in terms of physiological and meteorological factors, often ignoring unique regional aspects. Each of the existing PEMs has developed unique methods to estimate NPP and the combination of the most successful of these could lead to improvements. It may be beneficial to develop regional PEMs that can be combined under a global framework. The results of this review suggest the creation of a hybrid PEM could bring about a significant enhancement to the PEM methodology and thus terrestrial carbon flux modeling. Key items topping the PEM research agenda identified in this review include the following: LUE should not be assumed constant, but should vary by plant functional type (PFT) or photosynthetic pathway; evidence is mounting that PEMs should consider incorporating diffuse radiation; continue to pursue relationships between satellite-derived variables and LUE, GPP and autotrophic respiration (Ra); there is an urgent need for satellite-based

  11. TALIF measurements of oxygen atom density in the afterglow of a capillary nanosecond discharge

    NASA Astrophysics Data System (ADS)

    Klochko, A. V.; Lemainque, J.; Booth, J. P.; Starikovskaia, S. M.

    2015-04-01

    The atomic oxygen density has been measured in the afterglow of a capillary nanosecond discharge in 24-30 mbar synthetic air (N2 : O2 = 4 : 1) by the two-photon absorption laser-induced fluorescence (TALIF) technique, combined with absolute calibration by comparison with xenon TALIF. The discharge was initiated by a train of 30 ns FWHM pulses of alternating positive-negative-positive polarity, separated by 250 ns, with a train repetition frequency of 10 Hz. The amplitude of the first pulse was 10 kV in the cable. A flow of synthetic air through the tube provided complete gas renewal between pulse trains. The O-atom density measurements were made over the time interval 200 ns-2 µs after the initial pulse. The gas temperature was determined by analysis of the molecular nitrogen second positive system optical emission spectrum. The influence of the gas temperature on the atom density measurements, and the reactions producing O atoms, are discussed.

  12. A search for absorption features in the afterglow of the unusual GRB 130925A

    NASA Astrophysics Data System (ADS)

    Bellm, Eric

    2012-09-01

    GRB 130925A produced several emission episodes triggering Swift-BAT, Fermi-GBM, and MAXI. The extraordinary length of this emission--over 10^4 seconds--would give GRB 130925A one of the highest total durations ever observed for a gamma-ray burst. While the initial bursting phase was similar to that of the the relativistic tidal disruption event Swift J1644+57, starting at 10^4 seconds after the trigger this event has entered a steady decay phase without new bursts (www.swift.ac.uk/xrt_curves/00571830/). Its classification is thus uncertain, as neither the long GRB class nor Swift J1644 provide direct parallels. Our NuSTAR spectroscopy during the decay phase has revealed evidence for a broad absorption feature never previously observed for either GRB afterglows or for tidal disruption events. Chandra observations will enable searches for lower-energy lines which may constrain the ionization state of this unprecedented event.

  13. MITSuME: multicolor optical/NIR telescopes for GRB afterglows

    SciTech Connect

    Shimokawabe, Takashi; Kawai, Nobuyuki; Kotani, Taro; Yatsu, Yoichi; Ishimura, Takuto; Vasquez, Nicolas; Mori, Yuki; Kudo, Yusuke; Yoshida, Michitoshi; Yanagisawa, Kenshi; Nagayama, Shogo; Toda, Hiroyuki; Shimozu, Yasuhiro; Kuroda, Daisuke; Watanabe, Junichi; Fukushima, Hideo; Mori, Masaki

    2008-05-22

    Multicolor Imaging Telescopes for Survey and Monstrous Explosions (MITSuME) is built to perform multi-color photometry of NIR/optical afterglow covering the wavebands from K{sub s} to g' allowing the photometric redshift measurements up to z{approx_equal}10.Two 50 cm optical telescopes are built at Akeno, Yamanashi in eastern Japan, and at OAO, Okayama in western Japan. Each telescope has a Tricolor Camera, which allows us to take simultaneous images in g', R{sub c} and I{sub c} bands. These telescopes respond to GCN alerts and start taking series of tricolor images, which are immediately processed through the analys is pipeline on site. The pipeline consists of source finding, catalog matching, sky coordinates mapping to the image pixels, and photometry of the found sources. In addition, an automated search for an optical counterpart is performed.In addition, a wide-field (1 deg.) 91 cm NIR telescope is being built at OAO with filters in K{sub s}, H, J, and y bands.Summary of early results will be also presented.

  14. The effect of a direct current field on the microparticle charge in the plasma afterglow

    SciTech Connect

    Wörner, L.; Ivlev, A. V.; Huber, P.; Hagl, T.; Thomas, H. M.; Morfill, G. E.; Couëdel, L.; Schwabe, M.; Mikikian, M.; Boufendi, L.; Skvortsov, A.; Lipaev, A. M.; Molotkov, V. I.; Petrov, O. F.; Fortov, V. E.

    2013-12-15

    Residual charges of individual microparticles forming dense clouds were measured in a RF discharge afterglow. Experiments were performed under microgravity conditions on board the International Space Station, which ensured particle levitation inside the gas volume after the plasma switch-off. The distribution of residual charges as well as the spatial distribution of charged particles across the cloud were analyzed by applying a low-frequency voltage to the electrodes and measuring amplitudes of the resulting particle oscillations. Upon “free decharging” conditions, the charge distribution had a sharp peak at zero and was rather symmetric (with charges concentrated between −10e and +10e), yet positively and negatively charged particles were homogeneously distributed over the cloud. However, when decharging evolved in the presence of an external DC field (applied shortly before the plasma switch-off) practically all residual charges were positive. In this case, the overall charge distribution had a sharp peak at about +15e and was highly asymmetric, while the spatial distribution exhibited a significant charge gradient along the direction of the applied DC field.

  15. ON THE ORIGIN OF > 10 GeV PHOTONS IN GAMMA-RAY BURST AFTERGLOWS

    SciTech Connect

    Wang Xiangyu; Liu Ruoyu; Lemoine, Martin

    2013-07-10

    Fermi/LAT has detected long-lasting high-energy photons (>100 MeV) from gamma-ray bursts (GRBs), with the highest energy photons reaching about 100 GeV. One proposed scenario is that they are produced by high-energy electrons accelerated in GRB forward shocks via synchrotron radiation. We study the maximum synchrotron photon energy in this scenario, considering the properties of the microturbulence magnetic fields behind the shock, as revealed by recent particle-in-cell simulations and theoretical analyses of relativistic collisionless shocks. Due to the small-scale nature of the microturbulent magnetic field, the Bohm acceleration approximation, in which the scattering mean free path is equal to the particle Larmor radius, breaks down at such high energies. This effect leads to a typical maximum synchrotron photon of a few GeV at 100 s after the burst and this maximum synchrotron photon energy decreases quickly with time. We show that the fast decrease of the maximum synchrotron photon energy leads to a fast decay of the synchrotron flux. The 10-100 GeV photons detected after the prompt phase cannot be produced by the synchrotron mechanism. They could originate from the synchrotron self-Compton emission of the early afterglow if the circumburst density is sufficiently large, or from the external inverse Compton process in the presence of central X-ray emission, such as X-ray flares and prompt high-latitude X-ray emission.

  16. A possible macronova in the late afterglow of the long–short burst GRB 060614

    PubMed Central

    Yang, Bin; Jin, Zhi-Ping; Li, Xiang; Covino, Stefano; Zheng, Xian-Zhong; Hotokezaka, Kenta; Fan, Yi-Zhong; Piran, Tsvi; Wei, Da-Ming

    2015-01-01

    Long-duration (>2 s) γ-ray bursts that are believed to originate from the death of massive stars are expected to be accompanied by supernovae. GRB 060614, that lasted 102 s, lacks a supernova-like emission down to very stringent limits and its physical origin is still debated. Here we report the discovery of near-infrared bump that is significantly above the regular decaying afterglow. This red bump is inconsistent with even the weakest known supernova. However, it can arise from a Li-Paczyński macronova—the radioactive decay of debris following a compact binary merger. If this interpretation is correct, GRB 060614 arose from a compact binary merger rather than from the death of a massive star and it was a site of a significant production of heavy r-process elements. The significant ejected mass favours a black hole–neutron star merger but a double neutron star merger cannot be ruled out. PMID:26065563

  17. A possible macronova in the late afterglow of the long-short burst GRB 060614.

    PubMed

    Yang, Bin; Jin, Zhi-Ping; Li, Xiang; Covino, Stefano; Zheng, Xian-Zhong; Hotokezaka, Kenta; Fan, Yi-Zhong; Piran, Tsvi; Wei, Da-Ming

    2015-01-01

    Long-duration (>2 s) γ-ray bursts that are believed to originate from the death of massive stars are expected to be accompanied by supernovae. GRB 060614, that lasted 102 s, lacks a supernova-like emission down to very stringent limits and its physical origin is still debated. Here we report the discovery of near-infrared bump that is significantly above the regular decaying afterglow. This red bump is inconsistent with even the weakest known supernova. However, it can arise from a Li-Paczyński macronova--the radioactive decay of debris following a compact binary merger. If this interpretation is correct, GRB 060614 arose from a compact binary merger rather than from the death of a massive star and it was a site of a significant production of heavy r-process elements. The significant ejected mass favours a black hole-neutron star merger but a double neutron star merger cannot be ruled out. PMID:26065563

  18. The effect of a direct current field on the microparticle charge in the plasma afterglow

    NASA Astrophysics Data System (ADS)

    Wörner, L.; Ivlev, A. V.; Couëdel, L.; Huber, P.; Schwabe, M.; Hagl, T.; Mikikian, M.; Boufendi, L.; Skvortsov, A.; Lipaev, A. M.; Molotkov, V. I.; Petrov, O. F.; Fortov, V. E.; Thomas, H. M.; Morfill, G. E.

    2013-12-01

    Residual charges of individual microparticles forming dense clouds were measured in a RF discharge afterglow. Experiments were performed under microgravity conditions on board the International Space Station, which ensured particle levitation inside the gas volume after the plasma switch-off. The distribution of residual charges as well as the spatial distribution of charged particles across the cloud were analyzed by applying a low-frequency voltage to the electrodes and measuring amplitudes of the resulting particle oscillations. Upon "free decharging" conditions, the charge distribution had a sharp peak at zero and was rather symmetric (with charges concentrated between -10e and +10e), yet positively and negatively charged particles were homogeneously distributed over the cloud. However, when decharging evolved in the presence of an external DC field (applied shortly before the plasma switch-off) practically all residual charges were positive. In this case, the overall charge distribution had a sharp peak at about +15e and was highly asymmetric, while the spatial distribution exhibited a significant charge gradient along the direction of the applied DC field.

  19. Plasma decay in the afterglow of a high-voltage nanosecond discharge in air

    SciTech Connect

    Aleksandrov, N. L.; Anokhin, E. M.; Kindysheva, S. V.; Kirpichnikov, A. A.; Kosarev, I. N.; Nudnova, M. M.; Starikovskaya, S. M.; Starikovskii, A. Yu.

    2012-02-15

    The decay of air plasma produced by a high-voltage nanosecond discharge at room temperature and gas pressures in the range of 1-10 Torr was studied experimentally and theoretically. The time dependence of the electron density was measured with a microwave interferometer. The initial electron density was about 10{sup 12} cm{sup -3}. The discharge homogeneity was monitored using optical methods. The dynamics of the charged particle densities in the discharge afterglow was simulated by numerically solving the balance equations for electron and ions and the equation for the electron temperature. It was shown that, under these experimental conditions, plasma electrons are mainly lost due to dissociative and three-body recombination with ions. Agreement between the measured and calculated electron densities was achieved only when the rate constant of the three-body electron-ion recombination was increased by one order of magnitude and the temperature dependence of this rate constant was modified. This indicates that the mechanism for three-body recombination of molecular ions differs from that of the well-studied mechanism of atomic ion recombination.

  20. Measurement of proton transfer reaction rates in a microwave cavity discharge flowing afterglow

    NASA Astrophysics Data System (ADS)

    Brooke, George M., IV

    The reaction rate coefficients between the hydronium ion and the molecules ethene (C2H4), propene (C 3H6), 1-butene (C4H8) and hydrogen sulfide (H2S) were measured at 296 K. The measured reaction rates were compared to collision rates calculated using average dipole orientation (ADO) theory. Reaction efficiency depends primarily upon the proton affinity of the molecules. All the measurements were obtained using the newly developed microwave cavity discharge flowing afterglow (MCD-FA) apparatus. This device uses an Asmussen-type microwave cavity discharge ion source that is spatially separated from the flow tube, eliminating many of the problems inherent with the original FA devices. In addition to measuring reaction rate coefficients, the MCD-FA was shown to be an effective tool for measuring trace compounds in atmospheric air. This method has many advantages over current detection techniques since compounds can be detected in almost real time, large mass ranges can be scanned quickly, and repeated calibration is not required. Preliminary measurements were made of car exhaust and exhaled alveolar air. Car exhaust showed the presence of numerous hydrocarbons, such as butene, benzene and toluene while the exhaled alveolar air showed the presence of various volatile organic compounds such as methanol and acetone.

  1. Mechanics model for actin-based motility.

    PubMed

    Lin, Yuan

    2009-02-01

    We present here a mechanics model for the force generation by actin polymerization. The possible adhesions between the actin filaments and the load surface, as well as the nucleation and capping of filament tips, are included in this model on top of the well-known elastic Brownian ratchet formulation. A closed form solution is provided from which the force-velocity relationship, summarizing the mechanics of polymerization, can be drawn. Model predictions on the velocity of moving beads driven by actin polymerization are consistent with experiment observations. This model also seems capable of explaining the enhanced actin-based motility of Listeria monocytogenes and beads by the presence of Vasodilator-stimulated phosphoprotein, as observed in recent experiments.

  2. Mechanics model for actin-based motility

    NASA Astrophysics Data System (ADS)

    Lin, Yuan

    2009-02-01

    We present here a mechanics model for the force generation by actin polymerization. The possible adhesions between the actin filaments and the load surface, as well as the nucleation and capping of filament tips, are included in this model on top of the well-known elastic Brownian ratchet formulation. A closed form solution is provided from which the force-velocity relationship, summarizing the mechanics of polymerization, can be drawn. Model predictions on the velocity of moving beads driven by actin polymerization are consistent with experiment observations. This model also seems capable of explaining the enhanced actin-based motility of Listeria monocytogenes and beads by the presence of Vasodilator-stimulated phosphoprotein, as observed in recent experiments.

  3. Electrochemistry-based Battery Modeling for Prognostics

    NASA Technical Reports Server (NTRS)

    Daigle, Matthew J.; Kulkarni, Chetan Shrikant

    2013-01-01

    Batteries are used in a wide variety of applications. In recent years, they have become popular as a source of power for electric vehicles such as cars, unmanned aerial vehicles, and commericial passenger aircraft. In such application domains, it becomes crucial to both monitor battery health and performance and to predict end of discharge (EOD) and end of useful life (EOL) events. To implement such technologies, it is crucial to understand how batteries work and to capture that knowledge in the form of models that can be used by monitoring, diagnosis, and prognosis algorithms. In this work, we develop electrochemistry-based models of lithium-ion batteries that capture the significant electrochemical processes, are computationally efficient, capture the effects of aging, and are of suitable accuracy for reliable EOD prediction in a variety of usage profiles. This paper reports on the progress of such a model, with results demonstrating the model validity and accurate EOD predictions.

  4. REM observations of GRB 060418 and GRB 060607A: the onset of the afterglow and the initial fireball Lorentz factor determination

    NASA Astrophysics Data System (ADS)

    Molinari, E.; Vergani, S. D.; Malesani, D.; Covino, S.; D'Avanzo, P.; Chincarini, G.; Zerbi, F. M.; Antonelli, L. A.; Conconi, P.; Testa, V.; Tosti, G.; Vitali, F.; D'Alessio, F.; Malaspina, G.; Nicastro, L.; Palazzi, E.; Guetta, D.; Campana, S.; Goldoni, P.; Masetti, N.; Meurs, E. J. A.; Monfardini, A.; Norci, L.; Pian, E.; Piranomonte, S.; Rizzuto, D.; Stefanon, M.; Stella, L.; Tagliaferri, G.; Ward, P. A.; Ihle, G.; Gonzalez, L.; Pizarro, A.; Sinclaire, P.; Valenzuela, J.

    2007-07-01

    Context: Gamma-ray burst (GRB) emission is believed to originate in highly relativistic fireballs. Aims: Currently, only lower limits were securely set to the initial fireball Lorentz factor Γ_0. We aim to provide a direct measure of Γ_0. Methods: The early-time afterglow light curve carries information about Γ_0, which determines the time of the afterglow peak. We have obtained early observations of the near-infrared afterglows of GRB 060418 and GRB 060607A with the REM robotic telescope. Results: For both events, the afterglow peak could be clearly singled out, allowing a firm determination of the fireball Lorentz of Γ_0˜ 400, fully confirming the highly relativistic nature of GRB fireballs. The deceleration radius was inferred to be R_dec ≈ 1017 cm. This is much larger than the internal shocks radius (believed to power the prompt emission), thus providing further evidence for a different origin of the prompt and afterglow stages of the GRB. Tables 2 and 3 are only available in electronic form at http://www.aanda.org

  5. 3-D model-based vehicle tracking.

    PubMed

    Lou, Jianguang; Tan, Tieniu; Hu, Weiming; Yang, Hao; Maybank, Steven J

    2005-10-01

    This paper aims at tracking vehicles from monocular intensity image sequences and presents an efficient and robust approach to three-dimensional (3-D) model-based vehicle tracking. Under the weak perspective assumption and the ground-plane constraint, the movements of model projection in the two-dimensional image plane can be decomposed into two motions: translation and rotation. They are the results of the corresponding movements of 3-D translation on the ground plane (GP) and rotation around the normal of the GP, which can be determined separately. A new metric based on point-to-line segment distance is proposed to evaluate the similarity between an image region and an instantiation of a 3-D vehicle model under a given pose. Based on this, we provide an efficient pose refinement method to refine the vehicle's pose parameters. An improved EKF is also proposed to track and to predict vehicle motion with a precise kinematics model. Experimental results with both indoor and outdoor data show that the algorithm obtains desirable performance even under severe occlusion and clutter.

  6. 3-D model-based vehicle tracking.

    PubMed

    Lou, Jianguang; Tan, Tieniu; Hu, Weiming; Yang, Hao; Maybank, Steven J

    2005-10-01

    This paper aims at tracking vehicles from monocular intensity image sequences and presents an efficient and robust approach to three-dimensional (3-D) model-based vehicle tracking. Under the weak perspective assumption and the ground-plane constraint, the movements of model projection in the two-dimensional image plane can be decomposed into two motions: translation and rotation. They are the results of the corresponding movements of 3-D translation on the ground plane (GP) and rotation around the normal of the GP, which can be determined separately. A new metric based on point-to-line segment distance is proposed to evaluate the similarity between an image region and an instantiation of a 3-D vehicle model under a given pose. Based on this, we provide an efficient pose refinement method to refine the vehicle's pose parameters. An improved EKF is also proposed to track and to predict vehicle motion with a precise kinematics model. Experimental results with both indoor and outdoor data show that the algorithm obtains desirable performance even under severe occlusion and clutter. PMID:16238061

  7. Data-Flow Based Model Analysis

    NASA Technical Reports Server (NTRS)

    Saad, Christian; Bauer, Bernhard

    2010-01-01

    The concept of (meta) modeling combines an intuitive way of formalizing the structure of an application domain with a high expressiveness that makes it suitable for a wide variety of use cases and has therefore become an integral part of many areas in computer science. While the definition of modeling languages through the use of meta models, e.g. in Unified Modeling Language (UML), is a well-understood process, their validation and the extraction of behavioral information is still a challenge. In this paper we present a novel approach for dynamic model analysis along with several fields of application. Examining the propagation of information along the edges and nodes of the model graph allows to extend and simplify the definition of semantic constraints in comparison to the capabilities offered by e.g. the Object Constraint Language. Performing a flow-based analysis also enables the simulation of dynamic behavior, thus providing an "abstract interpretation"-like analysis method for the modeling domain.

  8. Ontology-based knowledge base model construction-OntoKBCF.

    PubMed

    Jing, Xia; Kay, Stephen; Hardiker, Nicholas; Marley, Tom

    2007-01-01

    Semantic web technologies are used in the construction of a bio-health knowledge base model, which, when coupled with an Electronic Health Record (EHR), is to be used by clinicians. Specifically, this ontology provides the basis for a domain knowledge resource that attempts to bridge biological and clinical information. The prototype is focused on a Cystic Fibrosis exemplar, and the content of the model includes: Cochrane reviews; a time-oriented description; gene therapy; and the most common cystic fibrosis gene mutations. The facts within the model range from nucleo-base mutation and amino acid change to clinical phenotype. The knowledge is represented by layers from the micro level to the macro level. Here, emphasis is placed upon the details between levels (i.e., the vertical axis) and these are made available to bridge the knowledge from different levels. The description of gender, age, mutation and clinical manifestations are clues for matching points within an EHR system. OWL is the ontology representation language used and the output from Protégé-OWL is a XML-based file format, which facilitates further application and communication.

  9. Knowledge Grid Based Knowledge Supply Model

    NASA Astrophysics Data System (ADS)

    Zhen, Lu; Jiang, Zuhua

    This paper is mainly concerned with a knowledge supply model in the environment of knowledge grid to realize the knowledge sharing globally. By integrating members, roles, and tasks in a workflow, three sorts of knowledge demands are gained. Based on knowledge demand information, a knowledge supply model is proposed for the purpose of delivering the right knowledge to the right persons. Knowledge grid, acting as a platform for implementing the knowledge supply, is also discussed mainly from the view of knowledge space. A prototype system of knowledge supply has been implemented and applied in product development.

  10. Process-Based Modeling of Constructed Wetlands

    NASA Astrophysics Data System (ADS)

    Baechler, S.; Brovelli, A.; Rossi, L.; Barry, D. A.

    2007-12-01

    Constructed wetlands (CWs) are widespread facilities for wastewater treatment. In subsurface flow wetlands, contaminated wastewater flows through a porous matrix, where oxidation and detoxification phenomena occur. Despite the large number of working CWs, system design and optimization are still mainly based upon empirical equations or simplified first-order kinetics. This results from an incomplete understanding of the system functioning, and may in turn hinder the performance and effectiveness of the treatment process. As a result, CWs are often considered not suitable to meet high water quality-standards, or to treat water contaminated with recalcitrant anthropogenic contaminants. To date, only a limited number of detailed numerical models have been developed and successfully applied to simulate constructed wetland behavior. Among these, one of the most complete and powerful is CW2D, which is based on Hydrus2D. The aim of this work is to develop a comprehensive simulator tailored to model the functioning of horizontal flow constructed wetlands and in turn provide a reliable design and optimization tool. The model is based upon PHWAT, a general reactive transport code for saturated flow. PHWAT couples MODFLOW, MT3DMS and PHREEQC-2 using an operator-splitting approach. The use of PHREEQC to simulate reactions allows great flexibility in simulating biogeochemical processes. The biogeochemical reaction network is similar to that of CW2D, and is based on the Activated Sludge Model (ASM). Kinetic oxidation of carbon sources and nutrient transformations (nitrogen and phosphorous primarily) are modeled via Monod-type kinetic equations. Oxygen dissolution is accounted for via a first-order mass-transfer equation. While the ASM model only includes a limited number of kinetic equations, the new simulator permits incorporation of an unlimited number of both kinetic and equilibrium reactions. Changes in pH, redox potential and surface reactions can be easily incorporated

  11. Model-based Tomographic Reconstruction Literature Search

    SciTech Connect

    Chambers, D H; Lehman, S K

    2005-11-30

    In the process of preparing a proposal for internal research funding, a literature search was conducted on the subject of model-based tomographic reconstruction (MBTR). The purpose of the search was to ensure that the proposed research would not replicate any previous work. We found that the overwhelming majority of work on MBTR which used parameterized models of the object was theoretical in nature. Only three researchers had applied the technique to actual data. In this note, we summarize the findings of the literature search.

  12. Modelling spatial association in pattern based land use simulation models.

    PubMed

    Anputhas, Markandu; Janmaat, Johannus John A; Nichol, Craig F; Wei, Xiaohua Adam

    2016-10-01

    Pattern based land use models are widely used to forecast land use change. These models predict land use change using driving variables observed on the studied landscape. Many of these models have a limited capacity to account for interactions between neighbouring land parcels. Some modellers have used common spatial statistical measures to incorporate neighbour effects. However, these approaches were developed for continuous variables, while land use classifications are categorical. Neighbour interactions are also endogenous, changing as the land use patterns change. In this study we describe a single variable measure that captures aspects of neighbour interactions as reflected in the land use pattern. We use a stepwise updating process to demonstrate how dynamic updating of our measure impacts on model forecasts. We illustrate these results using the CLUE-S (Conversion of Land Use and its Effects at Small regional extent) system to forecast land use change for the Deep Creek watershed in the northern Okanagan Valley of British Columbia, Canada. Results establish that our measure improves model calibration and that ignoring changing spatial influences biases land use change forecasts.

  13. Modelling spatial association in pattern based land use simulation models.

    PubMed

    Anputhas, Markandu; Janmaat, Johannus John A; Nichol, Craig F; Wei, Xiaohua Adam

    2016-10-01

    Pattern based land use models are widely used to forecast land use change. These models predict land use change using driving variables observed on the studied landscape. Many of these models have a limited capacity to account for interactions between neighbouring land parcels. Some modellers have used common spatial statistical measures to incorporate neighbour effects. However, these approaches were developed for continuous variables, while land use classifications are categorical. Neighbour interactions are also endogenous, changing as the land use patterns change. In this study we describe a single variable measure that captures aspects of neighbour interactions as reflected in the land use pattern. We use a stepwise updating process to demonstrate how dynamic updating of our measure impacts on model forecasts. We illustrate these results using the CLUE-S (Conversion of Land Use and its Effects at Small regional extent) system to forecast land use change for the Deep Creek watershed in the northern Okanagan Valley of British Columbia, Canada. Results establish that our measure improves model calibration and that ignoring changing spatial influences biases land use change forecasts. PMID:27420169

  14. Low-resolution Spectroscopy of Gamma-ray Burst Optical Afterglows: Biases in the Swift Sample and Characterization of the Absorbers

    NASA Astrophysics Data System (ADS)

    Fynbo, J. P. U.; Jakobsson, P.; Prochaska, J. X.; Malesani, D.; Ledoux, C.; de Ugarte Postigo, A.; Nardini, M.; Vreeswijk, P. M.; Wiersema, K.; Hjorth, J.; Sollerman, J.; Chen, H.-W.; Thöne, C. C.; Björnsson, G.; Bloom, J. S.; Castro-Tirado, A. J.; Christensen, L.; De Cia, A.; Fruchter, A. S.; Gorosabel, J.; Graham, J. F.; Jaunsen, A. O.; Jensen, B. L.; Kann, D. A.; Kouveliotou, C.; Levan, A. J.; Maund, J.; Masetti, N.; Milvang-Jensen, B.; Palazzi, E.; Perley, D. A.; Pian, E.; Rol, E.; Schady, P.; Starling, R. L. C.; Tanvir, N. R.; Watson, D. J.; Xu, D.; Augusteijn, T.; Grundahl, F.; Telting, J.; Quirion, P.-O.

    2009-12-01

    We present a sample of 77 optical afterglows (OAs) of Swift detected gamma-ray bursts (GRBs) for which spectroscopic follow-up observations have been secured. Our first objective is to measure the redshifts of the bursts. For the majority (90%) of the afterglows, the redshifts have been determined from the spectra. We provide line lists and equivalent widths (EWs) for all detected lines redward of Lyα covered by the spectra. In addition to the GRB absorption systems, these lists include line strengths for a total of 33 intervening absorption systems. We discuss to what extent the current sample of Swift bursts with OA spectroscopy is a biased subsample of all Swift detected GRBs. For that purpose we define an X-ray-selected statistical sample of Swift bursts with optimal conditions for ground-based follow-up from the period 2005 March to 2008 September; 146 bursts fulfill our sample criteria. We derive the redshift distribution for the statistical (X-ray selected) sample and conclude that less than 18% of Swift bursts can be at z > 7. We compare the high-energy properties (e.g., γ-ray (15-350 keV) fluence and duration, X-ray flux, and excess absorption) for three subsamples of bursts in the statistical sample: (1) bursts with redshifts measured from OA spectroscopy; (2) bursts with detected optical and/or near-IR afterglow, but no afterglow-based redshift; and (3) bursts with no detection of the OA. The bursts in group (1) have slightly higher γ-ray fluences and higher X-ray fluxes and significantly less excess X-ray absorption than bursts in the other two groups. In addition, the fractions of dark bursts, defined as bursts with an optical to X-ray slope βOX < 0.5, is 14% in group (1), 38% in group (2), and >39% in group (3). For the full sample, the dark burst fraction is constrained to be in the range 25%-42%. From this we conclude that the sample of GRBs with OA spectroscopy is not representative for all Swift bursts, most likely due to a bias against the

  15. Gamma-Ray Burst Afterglows as Probes of Environment and Blastwave Physics II: The Distribution of p and Structure of the Circumburst Medium

    NASA Technical Reports Server (NTRS)

    Starling, R. L. C.; vanderHorst, A. J.; Rol, E.; Wijers, R. A. M. J.; Kouveliotou, C.; Wiersema, K.; Curran, P. A.; Weltevrede, P.

    2007-01-01

    We constrain blastwave parameters and the circumburst media of a subsample of BeppoSAX Gamma-Ray Bursts. For this sample we derive the values of the injected electron energy distribution index, p, and the density structure index of the circumburst medium, k, from simultaneous spectral fits to their X-ray, optical and nIR afterglow data. The spectral fits have been done in count space and include the effects of metallicity, and are compared with the previously reported optical and X-ray temporal behaviour. Assuming the fireball model, we can find a mean value of p for the sample as a whole of 2.035. A statistical analysis Of the distribution demonstrates that the p values in this sample are inconsistent with a single universal value for p at the 3sigma level or greater. This approach provides us with a measured distribution of circumburst density structures rather than considering only the cases of k = 0 (homogeneous) and k = 2 (wind-like). We find five GRBs for which k can be well constrained, and in four of these cases the circumburst medium is clearly wind-like. The fifth source has a value of 0 less than or equal to k less than or equal to 1, consistent with a homogeneous circumburst medium.

  16. Agent Based Model of Livestock Movements

    NASA Astrophysics Data System (ADS)

    Miron, D. J.; Emelyanova, I. V.; Donald, G. E.; Garner, G. M.

    The modelling of livestock movements within Australia is of national importance for the purposes of the management and control of exotic disease spread, infrastructure development and the economic forecasting of livestock markets. In this paper an agent based model for the forecasting of livestock movements is presented. This models livestock movements from farm to farm through a saleyard. The decision of farmers to sell or buy cattle is often complex and involves many factors such as climate forecast, commodity prices, the type of farm enterprise, the number of animals available and associated off-shore effects. In this model the farm agent's intelligence is implemented using a fuzzy decision tree that utilises two of these factors. These two factors are the livestock price fetched at the last sale and the number of stock on the farm. On each iteration of the model farms choose either to buy, sell or abstain from the market thus creating an artificial supply and demand. The buyers and sellers then congregate at the saleyard where livestock are auctioned using a second price sealed bid. The price time series output by the model exhibits properties similar to those found in real livestock markets.

  17. Systems Engineering Interfaces: A Model Based Approach

    NASA Technical Reports Server (NTRS)

    Fosse, Elyse; Delp, Christopher

    2013-01-01

    Currently: Ops Rev developed and maintains a framework that includes interface-specific language, patterns, and Viewpoints. Ops Rev implements the framework to design MOS 2.0 and its 5 Mission Services. Implementation de-couples interfaces and instances of interaction Future: A Mission MOSE implements the approach and uses the model based artifacts for reviews. The framework extends further into the ground data layers and provides a unified methodology.

  18. Genome Informed Trait-Based Models

    NASA Astrophysics Data System (ADS)

    Karaoz, U.; Cheng, Y.; Bouskill, N.; Tang, J.; Beller, H. R.; Brodie, E.; Riley, W. J.

    2013-12-01

    Trait-based approaches are powerful tools for representing microbial communities across both spatial and temporal scales within ecosystem models. Trait-based models (TBMs) represent the diversity of microbial taxa as stochastic assemblages with a distribution of traits constrained by trade-offs between these traits. Such representation with its built-in stochasticity allows the elucidation of the interactions between the microbes and their environment by reducing the complexity of microbial community diversity into a limited number of functional ';guilds' and letting them emerge across spatio-temporal scales. From the biogeochemical/ecosystem modeling perspective, the emergent properties of the microbial community could be directly translated into predictions of biogeochemical reaction rates and microbial biomass. The accuracy of TBMs depends on the identification of key traits of the microbial community members and on the parameterization of these traits. Current approaches to inform TBM parameterization are empirical (i.e., based on literature surveys). Advances in omic technologies (such as genomics, metagenomics, metatranscriptomics, and metaproteomics) pave the way to better-initialize models that can be constrained in a generic or site-specific fashion. Here we describe the coupling of metagenomic data to the development of a TBM representing the dynamics of metabolic guilds from an organic carbon stimulated groundwater microbial community. Illumina paired-end metagenomic data were collected from the community as it transitioned successively through electron-accepting conditions (nitrate-, sulfate-, and Fe(III)-reducing), and used to inform estimates of growth rates and the distribution of metabolic pathways (i.e., aerobic and anaerobic oxidation, fermentation) across a spatially resolved TBM. We use this model to evaluate the emergence of different metabolisms and predict rates of biogeochemical processes over time. We compare our results to observational

  19. Model-based vision for space applications

    NASA Technical Reports Server (NTRS)

    Chaconas, Karen; Nashman, Marilyn; Lumia, Ronald

    1992-01-01

    This paper describes a method for tracking moving image features by combining spatial and temporal edge information with model based feature information. The algorithm updates the two-dimensional position of object features by correlating predicted model features with current image data. The results of the correlation process are used to compute an updated model. The algorithm makes use of a high temporal sampling rate with respect to spatial changes of the image features and operates in a real-time multiprocessing environment. Preliminary results demonstrate successful tracking for image feature velocities between 1.1 and 4.5 pixels every image frame. This work has applications for docking, assembly, retrieval of floating objects and a host of other space-related tasks.

  20. Constraints based analysis of extended cybernetic models.

    PubMed

    Mandli, Aravinda R; Venkatesh, Kareenhalli V; Modak, Jayant M

    2015-11-01

    The cybernetic modeling framework provides an interesting approach to model the regulatory phenomena occurring in microorganisms. In the present work, we adopt a constraints based approach to analyze the nonlinear behavior of the extended equations of the cybernetic model. We first show that the cybernetic model exhibits linear growth behavior under the constraint of no resource allocation for the induction of the key enzyme. We then quantify the maximum achievable specific growth rate of microorganisms on mixtures of substitutable substrates under various kinds of regulation and show its use in gaining an understanding of the regulatory strategies of microorganisms. Finally, we show that Saccharomyces cerevisiae exhibits suboptimal dynamic growth with a long diauxic lag phase when growing on a mixture of glucose and galactose and discuss on its potential to achieve optimal growth with a significantly reduced diauxic lag period. The analysis carried out in the present study illustrates the utility of adopting a constraints based approach to understand the dynamic growth strategies of microorganisms.

  1. Model-based vision for car following

    NASA Astrophysics Data System (ADS)

    Schneiderman, Henry; Nashman, Marilyn; Lumia, Ronald

    1993-08-01

    This paper describes a vision processing algorithm that supports autonomous car following. The algorithm visually tracks the position of a `lead vehicle' from the vantage of a pursuing `chase vehicle.' The algorithm requires a 2-D model of the back of the lead vehicle. This model is composed of line segments corresponding to features that give rise to strong edges. There are seven sequential stages of computation: (1) Extracting edge points; (2) Associating extracted edge points with the model features; (3) Determining the position of each model feature; (4) Determining the model position; (5) Updating the motion model of the object; (6) Predicting the position of the object in next image; (7) Predicting the location of all object features from prediction of object position. All processing is confined to the 2-D image plane. The 2-D model location computed in this processing is used to determine the position of the lead vehicle with respect to a 3-D coordinate frame affixed to the chase vehicle. This algorithm has been used as part of a complete system to drive an autonomous vehicle, a High Mobility Multipurpose Wheeled Vehicle (HMMWV) such that it follows a lead vehicle at speeds up to 35 km/hr. The algorithm runs at an update rate of 15 Hertz and has a worst case computational delay of 128 ms. The algorithm is implemented under the NASA/NBS Standard Reference Model for Telerobotic Control System Architecture (NASREM) and runs on a dedicated vision processing engine and a VME-based multiprocessor system.

  2. Ag/BiOBr Film in a Rotating-Disk Reactor Containing Long-Afterglow Phosphor for Round-the-Clock Photocatalysis.

    PubMed

    Yin, Haibo; Chen, Xiaofang; Hou, Rujing; Zhu, Huijuan; Li, Shiqing; Huo, Yuning; Li, Hexing

    2015-09-16

    Ag/BiOBr film coated on the glass substrate was synthesized by a solvothermal method and a subsequent photoreduction process. Such a Ag/BiOBr film was then adhered to a hollow rotating disk filled with long-afterglow phosphor inside the chamber. The Ag/BiOBr film exhibited high photocatalytic activity for organic pollutant degradation owing to the improved visible-light harvesting and the separation of photoinduced charges. The long-afterglow phosphor could absorb the excessive daylight and emit light around 488 nm, activating the Ag/BiOBr film to realize round-the-clock photocatalysis. Because the Ag nanoparticles could extend the light absorbance of the Ag/BiOBr film to wavelengths of around 500 nm via a surface plasma resonance effect, they played a key role in realizing photocatalysis induced by long-afterglow phosphor.

  3. Ag/BiOBr Film in a Rotating-Disk Reactor Containing Long-Afterglow Phosphor for Round-the-Clock Photocatalysis.

    PubMed

    Yin, Haibo; Chen, Xiaofang; Hou, Rujing; Zhu, Huijuan; Li, Shiqing; Huo, Yuning; Li, Hexing

    2015-09-16

    Ag/BiOBr film coated on the glass substrate was synthesized by a solvothermal method and a subsequent photoreduction process. Such a Ag/BiOBr film was then adhered to a hollow rotating disk filled with long-afterglow phosphor inside the chamber. The Ag/BiOBr film exhibited high photocatalytic activity for organic pollutant degradation owing to the improved visible-light harvesting and the separation of photoinduced charges. The long-afterglow phosphor could absorb the excessive daylight and emit light around 488 nm, activating the Ag/BiOBr film to realize round-the-clock photocatalysis. Because the Ag nanoparticles could extend the light absorbance of the Ag/BiOBr film to wavelengths of around 500 nm via a surface plasma resonance effect, they played a key role in realizing photocatalysis induced by long-afterglow phosphor. PMID:26317239

  4. Model-Based Method for Sensor Validation

    NASA Technical Reports Server (NTRS)

    Vatan, Farrokh

    2012-01-01

    Fault detection, diagnosis, and prognosis are essential tasks in the operation of autonomous spacecraft, instruments, and in situ platforms. One of NASA s key mission requirements is robust state estimation. Sensing, using a wide range of sensors and sensor fusion approaches, plays a central role in robust state estimation, and there is a need to diagnose sensor failure as well as component failure. Sensor validation can be considered to be part of the larger effort of improving reliability and safety. The standard methods for solving the sensor validation problem are based on probabilistic analysis of the system, from which the method based on Bayesian networks is most popular. Therefore, these methods can only predict the most probable faulty sensors, which are subject to the initial probabilities defined for the failures. The method developed in this work is based on a model-based approach and provides the faulty sensors (if any), which can be logically inferred from the model of the system and the sensor readings (observations). The method is also more suitable for the systems when it is hard, or even impossible, to find the probability functions of the system. The method starts by a new mathematical description of the problem and develops a very efficient and systematic algorithm for its solution. The method builds on the concepts of analytical redundant relations (ARRs).

  5. Fabric-based systems: model, tools, applications.

    SciTech Connect

    Wolinski, C.; Gokhale, M.; McCabe, K. P.

    2003-01-01

    A Fabric Based System is a parameterized cellular architecture in which an array of computing cells communicates with an embedded processor through a global memory . This architecture is customizable to different classes of applications by funtional unit, interconnect, and memory parameters, and can be instantiated efficiently on platform FPGAs . In previous work, we have demonstrated the advantage of reconfigurable fabrics for image and signal processing applications . Recently, we have build a Fabric Generator, a Java-based toolset that greatly accelerates construction of the fabrics presented in. A module-generation library is used to define, instantiate, and interconnect cells' datapaths . FG generates customized sequencers for individual cells or collections of cells . We describe the Fabric-Based System model, the FG toolset, and concrete realizations offabric architectures generated by FG on the Altera Excalibur ARM that can deliver 4.5 GigaMACs/s (8/16 bit data, Multiply-Accumulate) .

  6. SEP modeling based on the ENLIL global heliospheric model

    NASA Astrophysics Data System (ADS)

    Mays, M. L.; Luhmann, J. G.; Odstrcil, D.; Lee, C.; Bain, H. M.; Li, Y.; Schwadron, N.; Gorby, M.; Baker, D. N.; Dewey, R. M.; Larson, D. E.; Halekas, J. S.; Connerney, J. E. P.; von Rosenvinge, T. T.; Galvin, A. B.; McComas, D. J.

    2015-12-01

    The global 3D MHD WSA-ENLIL model provides a time-dependent background heliospheric description, into which a spherical shaped CME can be inserted. Understanding gradual SEP events (often driven by CMEs) well enough to forecast their properties at a given location requires a realistic picture of the global background solar wind through which the shocks and SEPs propagate. Accurate descriptions of the heliosphere, and hence modeled SEPs, are achieved by ENLIL only when the background solar wind is well-reproduced and CME parameters are accurate. It is clear from our preliminary runs that the CMEs sometimes generate multiple shocks, some of which fade while others merge and/or strengthen as they propagate. In order to completely characterize the SEP profiles observed at locations spread in longitude with the aid of these simulations it is essential to include all of the relevant CMEs and allow enough time for the events to propagate and interact. ENLIL provides solar wind parameters and additionally one can extract the magnetic topologies of observer-connected magnetic field lines and all plasma and shock properties along those field lines. ENLIL "likelihood/all-clear" forecasting maps provide expected intensity, timing/duration of events at locations throughout the heliosphere with "possible SEP affected areas" color-coded based on shock strength. ENLIL simulations are also useful to drive SEP models such as the Solar Energetic Particle Model (SEPMOD) and Earth-Moon-Mars Radiation Environment Module (EMMREM). In this presentation we demonstrate case studies of SEP event modeling at locations spread in longitude based on WSA-ENLIL+Cone simulations.

  7. Physics-based models of the plasmasphere

    SciTech Connect

    Jordanova, Vania K; Pierrard, Vivane; Goldstein, Jerry; Andr'e, Nicolas; Lemaire, Joseph F; Liemohn, Mike W; Matsui, H

    2008-01-01

    We describe recent progress in physics-based models of the plasmasphere using the Auid and the kinetic approaches. Global modeling of the dynamics and inAuence of the plasmasphere is presented. Results from global plasmasphere simulations are used to understand and quantify (i) the electric potential pattern and evolution during geomagnetic storms, and (ii) the inAuence of the plasmasphere on the excitation of electromagnetic ion cyclotron (ElvIIC) waves a.nd precipitation of energetic ions in the inner magnetosphere. The interactions of the plasmasphere with the ionosphere a.nd the other regions of the magnetosphere are pointed out. We show the results of simulations for the formation of the plasmapause and discuss the inAuence of plasmaspheric wind and of ultra low frequency (ULF) waves for transport of plasmaspheric material. Theoretical formulations used to model the electric field and plasma distribution in the plasmasphere are given. Model predictions are compared to recent CLUSTER and MAGE observations, but also to results of earlier models and satellite observations.

  8. Model based systems engineering for astronomical projects

    NASA Astrophysics Data System (ADS)

    Karban, R.; Andolfato, L.; Bristow, P.; Chiozzi, G.; Esselborn, M.; Schilling, M.; Schmid, C.; Sommer, H.; Zamparelli, M.

    2014-08-01

    Model Based Systems Engineering (MBSE) is an emerging field of systems engineering for which the System Modeling Language (SysML) is a key enabler for descriptive, prescriptive and predictive models. This paper surveys some of the capabilities, expectations and peculiarities of tools-assisted MBSE experienced in real-life astronomical projects. The examples range in depth and scope across a wide spectrum of applications (for example documentation, requirements, analysis, trade studies) and purposes (addressing a particular development need, or accompanying a project throughout many - if not all - its lifecycle phases, fostering reuse and minimizing ambiguity). From the beginnings of the Active Phasing Experiment, through VLT instrumentation, VLTI infrastructure, Telescope Control System for the E-ELT, until Wavefront Control for the E-ELT, we show how stepwise refinements of tools, processes and methods have provided tangible benefits to customary system engineering activities like requirement flow-down, design trade studies, interfaces definition, and validation, by means of a variety of approaches (like Model Checking, Simulation, Model Transformation) and methodologies (like OOSEM, State Analysis)

  9. Fault diagnosis based on continuous simulation models

    NASA Technical Reports Server (NTRS)

    Feyock, Stefan

    1987-01-01

    The results are described of an investigation of techniques for using continuous simulation models as basis for reasoning about physical systems, with emphasis on the diagnosis of system faults. It is assumed that a continuous simulation model of the properly operating system is available. Malfunctions are diagnosed by posing the question: how can we make the model behave like that. The adjustments that must be made to the model to produce the observed behavior usually provide definitive clues to the nature of the malfunction. A novel application of Dijkstra's weakest precondition predicate transformer is used to derive the preconditions for producing the required model behavior. To minimize the size of the search space, an envisionment generator based on interval mathematics was developed. In addition to its intended application, the ability to generate qualitative state spaces automatically from quantitative simulations proved to be a fruitful avenue of investigation in its own right. Implementations of the Dijkstra transform and the envisionment generator are reproduced in the Appendix.

  10. Flow based vs. demand based energy-water modelling

    NASA Astrophysics Data System (ADS)

    Rozos, Evangelos; Nikolopoulos, Dionysis; Efstratiadis, Andreas; Koukouvinos, Antonios; Makropoulos, Christos

    2015-04-01

    The water flow in hydro-power generation systems is often used downstream to cover other type of demands like irrigation and water supply. However, the typical case is that the energy demand (operation of hydro-power plant) and the water demand do not coincide. Furthermore, the water inflow into a reservoir is a stochastic process. Things become more complicated if renewable resources (wind-turbines or photovoltaic panels) are included into the system. For this reason, the assessment and optimization of the operation of hydro-power systems are challenging tasks that require computer modelling. This modelling should not only simulate the water budget of the reservoirs and the energy production/consumption (pumped-storage), but should also take into account the constraints imposed by the natural or artificial water network using a flow routing algorithm. HYDRONOMEAS, for example, uses an elegant mathematical approach (digraph) to calculate the flow in a water network based on: the demands (input timeseries), the water availability (simulated) and the capacity of the transmission components (properties of channels, rivers, pipes, etc.). The input timeseries of demand should be estimated by another model and linked to the corresponding network nodes. A model that could be used to estimate these timeseries is UWOT. UWOT is a bottom up urban water cycle model that simulates the generation, aggregation and routing of water demand signals. In this study, we explore the potentials of UWOT in simulating the operation of complex hydrosystems that include energy generation. The evident advantage of this approach is the use of a single model instead of one for estimation of demands and another for the system simulation. An application of UWOT in a large scale system is attempted in mainland Greece in an area extending over 130×170 km². The challenges, the peculiarities and the advantages of this approach are examined and critically discussed.

  11. Mathematical modeling of acid-base physiology

    PubMed Central

    Occhipinti, Rossana; Boron, Walter F.

    2015-01-01

    pH is one of the most important parameters in life, influencing virtually every biological process at the cellular, tissue, and whole-body level. Thus, for cells, it is critical to regulate intracellular pH (pHi) and, for multicellular organisms, to regulate extracellular pH (pHo). pHi regulation depends on the opposing actions of plasma-membrane transporters that tend to increase pHi, and others that tend to decrease pHi. In addition, passive fluxes of uncharged species (e.g., CO2, NH3) and charged species (e.g., HCO3− , NH4+) perturb pHi. These movements not only influence one another, but also perturb the equilibria of a multitude of intracellular and extracellular buffers. Thus, even at the level of a single cell, perturbations in acid-base reactions, diffusion, and transport are so complex that it is impossible to understand them without a quantitative model. Here we summarize some mathematical models developed to shed light onto the complex interconnected events triggered by acids-base movements. We then describe a mathematical model of a spherical cell–which to our knowledge is the first one capable of handling a multitude of buffer reaction–that our team has recently developed to simulate changes in pHi and pHo caused by movements of acid-base equivalents across the plasma membrane of a Xenopus oocyte. Finally, we extend our work to a consideration of the effects of simultaneous CO2 and HCO3− influx into a cell, and envision how future models might extend to other cell types (e.g., erythrocytes) or tissues (e.g., renal proximal-tubule epithelium) important for whole-body pH homeostasis. PMID:25617697

  12. Mathematical modeling of acid-base physiology.

    PubMed

    Occhipinti, Rossana; Boron, Walter F

    2015-01-01

    pH is one of the most important parameters in life, influencing virtually every biological process at the cellular, tissue, and whole-body level. Thus, for cells, it is critical to regulate intracellular pH (pHi) and, for multicellular organisms, to regulate extracellular pH (pHo). pHi regulation depends on the opposing actions of plasma-membrane transporters that tend to increase pHi, and others that tend to decrease pHi. In addition, passive fluxes of uncharged species (e.g., CO2, NH3) and charged species (e.g., HCO3(-), [Formula: see text] ) perturb pHi. These movements not only influence one another, but also perturb the equilibria of a multitude of intracellular and extracellular buffers. Thus, even at the level of a single cell, perturbations in acid-base reactions, diffusion, and transport are so complex that it is impossible to understand them without a quantitative model. Here we summarize some mathematical models developed to shed light onto the complex interconnected events triggered by acids-base movements. We then describe a mathematical model of a spherical cells-which to our knowledge is the first one capable of handling a multitude of buffer reactions-that our team has recently developed to simulate changes in pHi and pHo caused by movements of acid-base equivalents across the plasma membrane of a Xenopus oocyte. Finally, we extend our work to a consideration of the effects of simultaneous CO2 and HCO3(-) influx into a cell, and envision how future models might extend to other cell types (e.g., erythrocytes) or tissues (e.g., renal proximal-tubule epithelium) important for whole-body pH homeostasis.

  13. Design of a component-based integrated environmental modeling framework

    EPA Science Inventory

    Integrated environmental modeling (IEM) includes interdependent science-based components (e.g., models, databases, viewers, assessment protocols) that comprise an appropriate software modeling system. The science-based components are responsible for consuming and producing inform...

  14. Probing radical kinetics in the afterglow of pulsed discharges by absorption spectroscopy with light emitting diodes: Application to BCl radical

    NASA Astrophysics Data System (ADS)

    Vempaire, D.; Cunge, G.

    2009-01-01

    Measuring decay rates of radical densities in the afterglow of pulsed plasmas is a powerful approach to determine their gas phase and surface loss kinetics. We show that this measurement can be achieved by absorption spectroscopy with low cost and simple apparatus by using light emitting diodes as a light source. The feasibility is demonstrated by monitoring BCl radicals in pulsed low pressure high-density BCl3 plasmas. It is shown that BCl is lost both in the gas phase by reacting with Cl2 with a cross section of 9 Å2 and in the chamber walls with a sticking coefficient of about 0.3.

  15. Kinetics of positive ions and electrically neutral active particles in afterglow in neon at low pressure

    SciTech Connect

    Pejović, Milić M. Nešić, Nikola T.; Pejović, Momčilo M.

    2014-04-15

    Kinetics of positive ions and electrically neutral active particles formed during breakdown and successive discharge in neon-filled tube at 6.6 millibars pressure had been analyzed. This analysis was performed on the basis of mean value of electrical breakdown time delay t{sup ¯}{sub d} dependence on afterglow period τ (memory curve). It was shown that positive ions are present in the 1μs < τ < 30 ms interval, which is manifested through t{sup ¯}{sub d} slow increase with the increase of τ. A rapid t{sup ¯}{sub d} increase in the 30 ms < τ < 3 s interval is a consequence of significant decrease of positive ions concentration and dominant role in breakdown initiation have ground state nitrogen atoms, which further release secondary electrons from the cathode by catalytic recombination process. These atoms are formed during discharge by dissociation of ground state nitrogen molecules that are present as impurities in neon. For τ > 3 s, breakdown is initiated by cosmic rays and natural radioactivity. The increase of discharge current leads to decrease of t{sup ¯}{sub d} due to the increase of positive ions concentration in inter electrode gap. The increase of applied voltage also decreases t{sup ¯}{sub d} for τ > 30 ms due to the increase of the probability for initial electron to initiate breakdown. The presence of UV radiation leads to the decrease of t{sup ¯}{sub d} due to the increased electron yield caused by photoelectrons. The influence of photoelectrons on breakdown initiation can be noticed for τ > 0.1 ms, while they dominantly determine t{sup ¯}{sub d} for τ > 30 ms.

  16. Kinetics of positive ions and electrically neutral active particles in afterglow in neon at low pressure

    NASA Astrophysics Data System (ADS)

    Pejović, Milić M.; Nešić, Nikola T.; Pejović, Momčilo M.

    2014-04-01

    Kinetics of positive ions and electrically neutral active particles formed during breakdown and successive discharge in neon-filled tube at 6.6 millibars pressure had been analyzed. This analysis was performed on the basis of mean value of electrical breakdown time delay t¯d dependence on afterglow period τ (memory curve). It was shown that positive ions are present in the 1μs < τ < 30 ms interval, which is manifested through t ¯d slow increase with the increase of τ. A rapid t¯d increase in the 30 ms < τ < 3 s interval is a consequence of significant decrease of positive ions concentration and dominant role in breakdown initiation have ground state nitrogen atoms, which further release secondary electrons from the cathode by catalytic recombination process. These atoms are formed during discharge by dissociation of ground state nitrogen molecules that are present as impurities in neon. For τ > 3 s, breakdown is initiated by cosmic rays and natural radioactivity. The increase of discharge current leads to decrease of t¯d due to the increase of positive ions concentration in inter electrode gap. The increase of applied voltage also decreases t¯d for τ > 30 ms due to the increase of the probability for initial electron to initiate breakdown. The presence of UV radiation leads to the decrease of t¯d due to the increased electron yield caused by photoelectrons. The influence of photoelectrons on breakdown initiation can be noticed for τ > 0.1 ms, while they dominantly determine t¯d for τ > 30 ms.

  17. Model-based phase-shifting interferometer

    NASA Astrophysics Data System (ADS)

    Liu, Dong; Zhang, Lei; Shi, Tu; Yang, Yongying; Chong, Shiyao; Miao, Liang; Huang, Wei; Shen, Yibing; Bai, Jian

    2015-10-01

    A model-based phase-shifting interferometer (MPI) is developed, in which a novel calculation technique is proposed instead of the traditional complicated system structure, to achieve versatile, high precision and quantitative surface tests. In the MPI, the partial null lens (PNL) is employed to implement the non-null test. With some alternative PNLs, similar as the transmission spheres in ZYGO interferometers, the MPI provides a flexible test for general spherical and aspherical surfaces. Based on modern computer modeling technique, a reverse iterative optimizing construction (ROR) method is employed for the retrace error correction of non-null test, as well as figure error reconstruction. A self-compiled ray-tracing program is set up for the accurate system modeling and reverse ray tracing. The surface figure error then can be easily extracted from the wavefront data in forms of Zernike polynomials by the ROR method. Experiments of the spherical and aspherical tests are presented to validate the flexibility and accuracy. The test results are compared with those of Zygo interferometer (null tests), which demonstrates the high accuracy of the MPI. With such accuracy and flexibility, the MPI would possess large potential in modern optical shop testing.

  18. Cosmic emergy based ecological systems modelling

    NASA Astrophysics Data System (ADS)

    Chen, H.; Chen, G. Q.; Ji, X.

    2010-09-01

    Ecological systems modelling based on the unified biophysical measure of cosmic emergy in terms of embodied cosmic exergy is illustrated in this paper with ecological accounting, simulation and scenario analysis, by a case study for the regional socio-economic ecosystem associated with the municipality of Beijing. An urbanized regional ecosystem model with eight subsystems of natural support, agriculture, urban production, population, finance, land area, potential environmental impact, and culture is representatively presented in exergy circuit language with 12 state variables governing by corresponding ecodynamic equations, and 60 flows and auxiliary variables. To characterize the regional socio-economy as an ecosystem, a series of ecological indicators based on cosmic emergy are devised. For a systematic ecological account, cosmic exergy transformities are provided for various dimensions including climate flows, natural resources, industrial products, cultural products, population with educational hierarchy, and environmental emissions. For the urban ecosystem of Beijing in the period from 1990 to 2005, ecological accounting is carried out and characterized in full details. Taking 2000 as the starting point, systems modelling is realized to predict the urban evolution in a one hundred time horizon. For systems regulation, scenario analyses with essential policy-making implications are made to illustrate the long term systems effects of the expected water diversion and rise in energy price.

  19. Decay of the GRB 990123 optical afterglow: implications for the fireball model

    PubMed

    Castro-Tirado; Zapatero-Osorio; Caon; Cairos; Hjorth; Pedersen; Andersen; Gorosabel; Bartolini; Guarnieri; Piccioni; Frontera; Masetti; Palazzi; Pian; Greiner; Hudec; Sagar; Pandey; Mohan; Yadav; Nilakshi; Bjornsson; Jakobsson; Burud; et

    1999-03-26

    Broad-band (ultraviolet to near-infrared) observations of the intense gamma ray burst GRB 990123 started approximately 8.5 hours after the event and continued until 18 February 1999. When combined with other data, in particular from the Robotic Telescope and Transient Source Experiment (ROTSE) and the Hubble Space Telescope (HST), evidence emerges for a smoothly declining light curve, suggesting some color dependence that could be related to a cooling break passing the ultraviolet-optical band at about 1 day after the high-energy event. The steeper decline rate seen after 1.5 to 2 days may be evidence for a collimated jet pointing toward the observer.

  20. Decay of the GRB 990123 optical afterglow: implications for the fireball model

    PubMed

    Castro-Tirado; Zapatero-Osorio; Caon; Cairos; Hjorth; Pedersen; Andersen; Gorosabel; Bartolini; Guarnieri; Piccioni; Frontera; Masetti; Palazzi; Pian; Greiner; Hudec; Sagar; Pandey; Mohan; Yadav; Nilakshi; Bjornsson; Jakobsson; Burud; et

    1999-03-26

    Broad-band (ultraviolet to near-infrared) observations of the intense gamma ray burst GRB 990123 started approximately 8.5 hours after the event and continued until 18 February 1999. When combined with other data, in particular from the Robotic Telescope and Transient Source Experiment (ROTSE) and the Hubble Space Telescope (HST), evidence emerges for a smoothly declining light curve, suggesting some color dependence that could be related to a cooling break passing the ultraviolet-optical band at about 1 day after the high-energy event. The steeper decline rate seen after 1.5 to 2 days may be evidence for a collimated jet pointing toward the observer. PMID:10092226

  1. Rainwater harvesting: model-based design evaluation.

    PubMed

    Ward, S; Memon, F A; Butler, D

    2010-01-01

    The rate of uptake of rainwater harvesting (RWH) in the UK has been slow to date, but is expected to gain momentum in the near future. The designs of two different new-build rainwater harvesting systems, based on simple methods, are evaluated using three different design methods, including a continuous simulation modelling approach. The RWH systems are shown to fulfill 36% and 46% of WC demand. Financial analyses reveal that RWH systems within large commercial buildings maybe more financially viable than smaller domestic systems. It is identified that design methods based on simple approaches generate tank sizes substantially larger than the continuous simulation. Comparison of the actual tank sizes and those calculated using continuous simulation established that the tanks installed are oversized for their associated demand level and catchment size. Oversizing tanks can lead to excessive system capital costs, which currently hinders the uptake of systems. Furthermore, it is demonstrated that the catchment area size is often overlooked when designing UK-based RWH systems. With respect to these findings, a recommendation for a transition from the use of simple tools to continuous simulation models is made.

  2. Model-Based Fault Tolerant Control

    NASA Technical Reports Server (NTRS)

    Kumar, Aditya; Viassolo, Daniel

    2008-01-01

    The Model Based Fault Tolerant Control (MBFTC) task was conducted under the NASA Aviation Safety and Security Program. The goal of MBFTC is to develop and demonstrate real-time strategies to diagnose and accommodate anomalous aircraft engine events such as sensor faults, actuator faults, or turbine gas-path component damage that can lead to in-flight shutdowns, aborted take offs, asymmetric thrust/loss of thrust control, or engine surge/stall events. A suite of model-based fault detection algorithms were developed and evaluated. Based on the performance and maturity of the developed algorithms two approaches were selected for further analysis: (i) multiple-hypothesis testing, and (ii) neural networks; both used residuals from an Extended Kalman Filter to detect the occurrence of the selected faults. A simple fusion algorithm was implemented to combine the results from each algorithm to obtain an overall estimate of the identified fault type and magnitude. The identification of the fault type and magnitude enabled the use of an online fault accommodation strategy to correct for the adverse impact of these faults on engine operability thereby enabling continued engine operation in the presence of these faults. The performance of the fault detection and accommodation algorithm was extensively tested in a simulation environment.

  3. Model Based Autonomy for Robust Mars Operations

    NASA Technical Reports Server (NTRS)

    Kurien, James A.; Nayak, P. Pandurang; Williams, Brian C.; Lau, Sonie (Technical Monitor)

    1998-01-01

    Space missions have historically relied upon a large ground staff, numbering in the hundreds for complex missions, to maintain routine operations. When an anomaly occurs, this small army of engineers attempts to identify and work around the problem. A piloted Mars mission, with its multiyear duration, cost pressures, half-hour communication delays and two-week blackouts cannot be closely controlled by a battalion of engineers on Earth. Flight crew involvement in routine system operations must also be minimized to maximize science return. It also may be unrealistic to require the crew have the expertise in each mission subsystem needed to diagnose a system failure and effect a timely repair, as engineers did for Apollo 13. Enter model-based autonomy, which allows complex systems to autonomously maintain operation despite failures or anomalous conditions, contributing to safe, robust, and minimally supervised operation of spacecraft, life support, In Situ Resource Utilization (ISRU) and power systems. Autonomous reasoning is central to the approach. A reasoning algorithm uses a logical or mathematical model of a system to infer how to operate the system, diagnose failures and generate appropriate behavior to repair or reconfigure the system in response. The 'plug and play' nature of the models enables low cost development of autonomy for multiple platforms. Declarative, reusable models capture relevant aspects of the behavior of simple devices (e.g. valves or thrusters). Reasoning algorithms combine device models to create a model of the system-wide interactions and behavior of a complex, unique artifact such as a spacecraft. Rather than requiring engineers to all possible interactions and failures at design time or perform analysis during the mission, the reasoning engine generates the appropriate response to the current situation, taking into account its system-wide knowledge, the current state, and even sensor failures or unexpected behavior.

  4. Factor-based Geostatistics for Groundwater Modeling

    NASA Astrophysics Data System (ADS)

    Savelyeva, E.; Pavlova, M.

    2012-04-01

    Analysis of groundwater levels is an important stage preceding modeling the filtration and migration processes in the hydro-geological environment. The boundary conditions are due to a pressure field, which strongly depends on groundwater levels, their spatial and temporal variability. Hydro-physical measurements are usually performed at a set of unhomogeneously spatially distributed wells according to some temporal scheme. Thus, it is an irregular spatio-temporal data set with a whole luggage of problems concerning organization of a spatio-temporal metrics system. These problems also affect modeling of a spatio-temporal correlation structure. There are different ways how to overcome these problems and obtain a reasonable model of spatio-temporal correlation structures. But still all these approaches are limited in future forecasting features. This work proposes an alternative approach - a factor-based space-time geostatistics. This method opens a set of possibilities concerning future modeling: possibility to use additional information to present different future scenario, characterization of uncertainty, probabilistic description of critical events. The basic idea is to replace a system of spatially correlated wells by a set of independent factors compressing data with a possibility of back transformation at the prescribed level of accuracy. Factors can be obtained by principle component analysis, independent sources and artificial neural network with a "bottle-neck". The selection of a method depends on the features of initial data and the process under study. All factors are time series nevertheless how they were obtained. A set of factors contains the main features of the groundwater level patterns. Groundwater levels modeling and forecasting is performed through modeling of these time series. This work considers three different stochastic approaches for modeling and forecasting of time series with hydrological origins: stochastic process with a deterministic

  5. Physiologically based quantitative modeling of unihemispheric sleep.

    PubMed

    Kedziora, D J; Abeysuriya, R G; Phillips, A J K; Robinson, P A

    2012-12-01

    Unihemispheric sleep has been observed in numerous species, including birds and aquatic mammals. While knowledge of its functional role has been improved in recent years, the physiological mechanisms that generate this behavior remain poorly understood. Here, unihemispheric sleep is simulated using a physiologically based quantitative model of the mammalian ascending arousal system. The model includes mutual inhibition between wake-promoting monoaminergic nuclei (MA) and sleep-promoting ventrolateral preoptic nuclei (VLPO), driven by circadian and homeostatic drives as well as cholinergic and orexinergic input to MA. The model is extended here to incorporate two distinct hemispheres and their interconnections. It is postulated that inhibitory connections between VLPO nuclei in opposite hemispheres are responsible for unihemispheric sleep, and it is shown that contralateral inhibitory connections promote unihemispheric sleep while ipsilateral inhibitory connections promote bihemispheric sleep. The frequency of alternating unihemispheric sleep bouts is chiefly determined by sleep homeostasis and its corresponding time constant. It is shown that the model reproduces dolphin sleep, and that the sleep regimes of humans, cetaceans, and fur seals, the latter both terrestrially and in a marine environment, require only modest changes in contralateral connection strength and homeostatic time constant. It is further demonstrated that fur seals can potentially switch between their terrestrial bihemispheric and aquatic unihemispheric sleep patterns by varying just the contralateral connection strength. These results provide experimentally testable predictions regarding the differences between species that sleep bihemispherically and unihemispherically. PMID:22960411

  6. Particle-based model for skiing traffic

    NASA Astrophysics Data System (ADS)

    Holleczek, Thomas; Tröster, Gerhard

    2012-05-01

    We develop and investigate a particle-based model for ski slope traffic. Skiers are modeled as particles with a mass that are exposed to social and physical forces, which define the riding behavior of skiers during their descents on ski slopes. We also report position and speed data of 21 skiers recorded with GPS-equipped cell phones on two ski slopes. A comparison of these data with the trajectories resulting from computer simulations of our model shows a good correspondence. A study of the relationship among the density, speed, and flow of skiers reveals that congestion does not occur even with arrival rates of skiers exceeding the maximum ski lift capacity. In a sensitivity analysis, we identify the kinetic friction coefficient of skis on snow, the skier mass, the range of repelling social forces, and the arrival rate of skiers as the crucial parameters influencing the simulation results. Our model allows for the prediction of speed zones and skier densities on ski slopes, which is important in the prevention of skiing accidents.

  7. Rough surface scattering based on facet model

    NASA Technical Reports Server (NTRS)

    Khamsi, H. R.; Fung, A. K.; Ulaby, F. T.

    1974-01-01

    A model for the radar return from bare ground was developed to calculate the radar cross section of bare ground and the effect of the frequency averaging on the reduction of the variance of the return. It is shown that, by assuming that the distribution of the slope to be Gaussian and that the distribution of the length of the facet to be in the form of the positive side of a Gaussian distribution, the results are in good agreement with experimental data collected by an 8- to 18-GHz radar spectrometer system. It is also shown that information on the exact correlation length of the small structure on the ground is not necessary; an effective correlation length may be calculated based on the facet model and the wavelength of the incident wave.

  8. Model-based segmentation of hand radiographs

    NASA Astrophysics Data System (ADS)

    Weiler, Frank; Vogelsang, Frank

    1998-06-01

    An important procedure in pediatrics is to determine the skeletal maturity of a patient from radiographs of the hand. There is great interest in the automation of this tedious and time-consuming task. We present a new method for the segmentation of the bones of the hand, which allows the assessment of the skeletal maturity with an appropriate database of reference bones, similar to the atlas based methods. The proposed algorithm uses an extended active contour model for the segmentation of the hand bones, which incorporates a-priori knowledge of shape and topology of the bones in an additional energy term. This `scene knowledge' is integrated in a complex hierarchical image model, that is used for the image analysis task.

  9. Agent based modeling in tactical wargaming

    NASA Astrophysics Data System (ADS)

    James, Alex; Hanratty, Timothy P.; Tuttle, Daniel C.; Coles, John B.

    2016-05-01

    Army staffs at division, brigade, and battalion levels often plan for contingency operations. As such, analysts consider the impact and potential consequences of actions taken. The Army Military Decision-Making Process (MDMP) dictates identification and evaluation of possible enemy courses of action; however, non-state actors often do not exhibit the same level and consistency of planned actions that the MDMP was originally designed to anticipate. The fourth MDMP step is a particular challenge, wargaming courses of action within the context of complex social-cultural behaviors. Agent-based Modeling (ABM) and its resulting emergent behavior is a potential solution to model terrain in terms of the human domain and improve the results and rigor of the traditional wargaming process.

  10. A burst in a wind bubble and the impact on baryonic ejecta: high-energy gamma-ray flashes and afterglows from fast radio bursts and pulsar-driven supernova remnants

    NASA Astrophysics Data System (ADS)

    Murase, Kohta; Kashiyama, Kazumi; Mészáros, Peter

    2016-09-01

    Tenuous wind bubbles, which are formed by the spin-down activity of central compact remnants, are relevant in some models of fast radio bursts (FRBs) and superluminous supernovae (SNe). We study their high-energy signatures, focusing on the role of pair-enriched bubbles produced by young magnetars, rapidly rotating neutron stars, and magnetized white dwarfs. (i) First, we study the nebular properties and the conditions allowing for escape of high-energy gamma-rays and radio waves, showing that their escape is possible for nebulae with ages of ≳10-100 yr. In the rapidly rotating neutron star scenario, we find that radio emission from the quasi-steady nebula itself may be bright enough to be detected especially at sub-mm frequencies, which is relevant as a possible counterpart of pulsar-driven SNe and FRBs. (ii) Secondly, we consider the fate of bursting emission in the nebulae. We suggest that an impulsive burst may lead to a highly relativistic flow, which would interact with the nebula. If the shocked nebula is still relativistic, pre-existing non-thermal particles in the nebula can be significantly boosted by the forward shock, leading to short-duration (maybe millisecond or longer) high-energy gamma-ray flashes. Possible dissipation at the reverse shock may also lead to gamma-ray emission. (iii) After such flares, interactions with the baryonic ejecta may lead to afterglow emission with a duration of days to weeks. In the magnetar scenario, this burst-in-bubble model leads to the expectation that nearby (≲10-100 Mpc) high-energy gamma-ray flashes may be detected by the High-Altitude Water Cherenkov Observatory and the Cherenkov Telescope Array, and the subsequent afterglow emission may be seen by radio telescopes such as the Very Large Array. (iv) Finally, we discuss several implications specific to FRBs, including constraints on the emission regions and limits on soft gamma-ray counterparts.

  11. Model-based neuroimaging for cognitive computing.

    PubMed

    Poznanski, Roman R

    2009-09-01

    The continuity of the mind is suggested to mean the continuous spatiotemporal dynamics arising from the electrochemical signature of the neocortex: (i) globally through volume transmission in the gray matter as fields of neural activity, and (ii) locally through extrasynaptic signaling between fine distal dendrites of cortical neurons. If the continuity of dynamical systems across spatiotemporal scales defines a stream of consciousness then intentional metarepresentations as templates of dynamic continuity allow qualia to be semantically mapped during neuroimaging of specific cognitive tasks. When interfaced with a computer, such model-based neuroimaging requiring new mathematics of the brain will begin to decipher higher cognitive operations not possible with existing brain-machine interfaces.

  12. SAT-Based Model Checking without Unrolling

    NASA Astrophysics Data System (ADS)

    Bradley, Aaron R.

    A new form of SAT-based symbolic model checking is described. Instead of unrolling the transition relation, it incrementally generates clauses that are inductive relative to (and augment) stepwise approximate reachability information. In this way, the algorithm gradually refines the property, eventually producing either an inductive strengthening of the property or a counterexample trace. Our experimental studies show that induction is a powerful tool for generalizing the unreachability of given error states: it can refine away many states at once, and it is effective at focusing the proof search on aspects of the transition system relevant to the property. Furthermore, the incremental structure of the algorithm lends itself to a parallel implementation.

  13. Ontology-Based Model Of Firm Competitiveness

    NASA Astrophysics Data System (ADS)

    Deliyska, Boryana; Stoenchev, Nikolay

    2010-10-01

    Competitiveness is important characteristics of each business organization (firm, company, corporation etc). It is of great significance for the organization existence and defines evaluation criteria of business success at microeconomical level. Each criterium comprises set of indicators with specific weight coefficients. In the work an ontology-based model of firm competitiveness is presented as a set of several mutually connected ontologies. It would be useful for knowledge structuring, standardization and sharing among experts and software engineers who develop application in the domain. Then the assessment of the competitiveness of various business organizations could be generated more effectively.

  14. Model-based vision using geometric hashing

    NASA Astrophysics Data System (ADS)

    Akerman, Alexander, III; Patton, Ronald

    1991-04-01

    The Geometric Hashing technique developed by the NYU Courant Institute has been applied to various automatic target recognition applications. In particular, I-MATH has extended the hashing algorithm to perform automatic target recognition ofsynthetic aperture radar (SAR) imagery. For this application, the hashing is performed upon the geometric locations of dominant scatterers. In addition to being a robust model-based matching algorithm -- invariant under translation, scale, and 3D rotations of the target -- hashing is of particular utility because it can still perform effective matching when the target is partially obscured. Moreover, hashing is very amenable to a SIMD parallel processing architecture, and thus potentially realtime implementable.

  15. Python-Based Applications for Hydrogeological Modeling

    NASA Astrophysics Data System (ADS)

    Khambhammettu, P.

    2013-12-01

    Python is a general-purpose, high-level programming language whose design philosophy emphasizes code readability. Add-on packages supporting fast array computation (numpy), plotting (matplotlib), scientific /mathematical Functions (scipy), have resulted in a powerful ecosystem for scientists interested in exploratory data analysis, high-performance computing and data visualization. Three examples are provided to demonstrate the applicability of the Python environment in hydrogeological applications. Python programs were used to model an aquifer test and estimate aquifer parameters at a Superfund site. The aquifer test conducted at a Groundwater Circulation Well was modeled with the Python/FORTRAN-based TTIM Analytic Element Code. The aquifer parameters were estimated with PEST such that a good match was produced between the simulated and observed drawdowns. Python scripts were written to interface with PEST and visualize the results. A convolution-based approach was used to estimate source concentration histories based on observed concentrations at receptor locations. Unit Response Functions (URFs) that relate the receptor concentrations to a unit release at the source were derived with the ATRANS code. The impact of any releases at the source could then be estimated by convolving the source release history with the URFs. Python scripts were written to compute and visualize receptor concentrations for user-specified source histories. The framework provided a simple and elegant way to test various hypotheses about the site. A Python/FORTRAN-based program TYPECURVEGRID-Py was developed to compute and visualize groundwater elevations and drawdown through time in response to a regional uniform hydraulic gradient and the influence of pumping wells using either the Theis solution for a fully-confined aquifer or the Hantush-Jacob solution for a leaky confined aquifer. The program supports an arbitrary number of wells that can operate according to arbitrary schedules. The

  16. Biologically based multistage modeling of radiation effects

    SciTech Connect

    William Hazelton; Suresh Moolgavkar; E. Georg Luebeck

    2005-08-30

    This past year we have made substantial progress in modeling the contribution of homeostatic regulation to low-dose radiation effects and carcinogenesis. We have worked to refine and apply our multistage carcinogenesis models to explicitly incorporate cell cycle states, simple and complex damage, checkpoint delay, slow and fast repair, differentiation, and apoptosis to study the effects of low-dose ionizing radiation in mouse intestinal crypts, as well as in other tissues. We have one paper accepted for publication in ''Advances in Space Research'', and another manuscript in preparation describing this work. I also wrote a chapter describing our combined cell-cycle and multistage carcinogenesis model that will be published in a book on stochastic carcinogenesis models edited by Wei-Yuan Tan. In addition, we organized and held a workshop on ''Biologically Based Modeling of Human Health Effects of Low dose Ionizing Radiation'', July 28-29, 2005 at Fred Hutchinson Cancer Research Center in Seattle, Washington. We had over 20 participants, including Mary Helen Barcellos-Hoff as keynote speaker, talks by most of the low-dose modelers in the DOE low-dose program, experimentalists including Les Redpath (and Mary Helen), Noelle Metting from DOE, and Tony Brooks. It appears that homeostatic regulation may be central to understanding low-dose radiation phenomena. The primary effects of ionizing radiation (IR) are cell killing, delayed cell cycling, and induction of mutations. However, homeostatic regulation causes cells that are killed or damaged by IR to eventually be replaced. Cells with an initiating mutation may have a replacement advantage, leading to clonal expansion of these initiated cells. Thus we have focused particularly on modeling effects that disturb homeostatic regulation as early steps in the carcinogenic process. There are two primary considerations that support our focus on homeostatic regulation. First, a number of epidemiologic studies using multistage

  17. Image-Based Modeling of Trabecular Bones

    NASA Astrophysics Data System (ADS)

    Rajapakse, Chamith; Gunaratne, Gemunu

    2004-10-01

    Osteoporosis is a major health problem in the U.S. today. The detection and treatment of osteoporosis is currently based on Bone Mineral Density (BMD) measurements. Recent evidence suggests that the low bone mass alone does not account for the entire risk of osteoporotic fractures. It is also been known that the trabecular regions of bones play a major role in the bone strength . Trabecular bone has a complex structure with substantial heterogeneity, anisotropy and asymmetry. Although these properties effect BMD, the role of architecture and tissue material remain uncertain. Computer modeling of trabecular bone can be used predict responses that cannot be obtained experimentally, and they can compute responses that cannot be measured in-vivo. Due to the complexity of the Trabecular Architecture (TA) a model system based on scanned digital images is introduced to get substantial insight of TA and to predict the failure behavior. It is assumed that the added insight provided by these studies will lead to improved diagnostics and treatments of patient-specific osteoporotic fractures.

  18. Models-Based Practice: Great White Hope or White Elephant?

    ERIC Educational Resources Information Center

    Casey, Ashley

    2014-01-01

    Background: Many critical curriculum theorists in physical education have advocated a model- or models-based approach to teaching in the subject. This paper explores the literature base around models-based practice (MBP) and asks if this multi-models approach to curriculum planning has the potential to be the great white hope of pedagogical change…

  19. Model-based estimation of knee stiffness.

    PubMed

    Pfeifer, Serge; Vallery, Heike; Hardegger, Michael; Riener, Robert; Perreault, Eric J

    2012-09-01

    During natural locomotion, the stiffness of the human knee is modulated continuously and subconsciously according to the demands of activity and terrain. Given modern actuator technology, powered transfemoral prostheses could theoretically provide a similar degree of sophistication and function. However, experimentally quantifying knee stiffness modulation during natural gait is challenging. Alternatively, joint stiffness could be estimated in a less disruptive manner using electromyography (EMG) combined with kinetic and kinematic measurements to estimate muscle force, together with models that relate muscle force to stiffness. Here we present the first step in that process, where we develop such an approach and evaluate it in isometric conditions, where experimental measurements are more feasible. Our EMG-guided modeling approach allows us to consider conditions with antagonistic muscle activation, a phenomenon commonly observed in physiological gait. Our validation shows that model-based estimates of knee joint stiffness coincide well with experimental data obtained using conventional perturbation techniques. We conclude that knee stiffness can be accurately estimated in isometric conditions without applying perturbations, which presents an important step toward our ultimate goal of quantifying knee stiffness during gait.

  20. Model-based estimation of individual fitness

    USGS Publications Warehouse

    Link, W.A.; Cooch, E.G.; Cam, E.

    2002-01-01

    Fitness is the currency of natural selection, a measure of the propagation rate of genotypes into future generations. Its various definitions have the common feature that they are functions of survival and fertility rates. At the individual level, the operative level for natural selection, these rates must be understood as latent features, genetically determined propensities existing at birth. This conception of rates requires that individual fitness be defined and estimated by consideration of the individual in a modelled relation to a group of similar individuals; the only alternative is to consider a sample of size one, unless a clone of identical individuals is available. We present hierarchical models describing individual heterogeneity in survival and fertility rates and allowing for associations between these rates at the individual level. We apply these models to an analysis of life histories of Kittiwakes (Rissa tridactyla ) observed at several colonies on the Brittany coast of France. We compare Bayesian estimation of the population distribution of individual fitness with estimation based on treating individual life histories in isolation, as samples of size one (e.g. McGraw & Caswell, 1996).

  1. Model-based estimation of individual fitness

    USGS Publications Warehouse

    Link, W.A.; Cooch, E.G.; Cam, E.

    2002-01-01

    Fitness is the currency of natural selection, a measure of the propagation rate of genotypes into future generations. Its various definitions have the common feature that they are functions of survival and fertility rates. At the individual level, the operative level for natural selection, these rates must be understood as latent features, genetically determined propensities existing at birth. This conception of rates requires that individual fitness be defined and estimated by consideration of the individual in a modelled relation to a group of similar individuals; the only alternative is to consider a sample of size one, unless a clone of identical individuals is available. We present hierarchical models describing individual heterogeneity in survival and fertility rates and allowing for associations between these rates at the individual level. We apply these models to an analysis of life histories of Kittiwakes (Rissa tridactyla) observed at several colonies on the Brittany coast of France. We compare Bayesian estimation of the population distribution of individual fitness with estimation based on treating individual life histories in isolation, as samples of size one (e.g. McGraw and Caswell, 1996).

  2. Model-Based Estimation of Knee Stiffness

    PubMed Central

    Pfeifer, Serge; Vallery, Heike; Hardegger, Michael; Riener, Robert; Perreault, Eric J.

    2013-01-01

    During natural locomotion, the stiffness of the human knee is modulated continuously and subconsciously according to the demands of activity and terrain. Given modern actuator technology, powered transfemoral prostheses could theoretically provide a similar degree of sophistication and function. However, experimentally quantifying knee stiffness modulation during natural gait is challenging. Alternatively, joint stiffness could be estimated in a less disruptive manner using electromyography (EMG) combined with kinetic and kinematic measurements to estimate muscle force, together with models that relate muscle force to stiffness. Here we present the first step in that process, where we develop such an approach and evaluate it in isometric conditions, where experimental measurements are more feasible. Our EMG-guided modeling approach allows us to consider conditions with antagonistic muscle activation, a phenomenon commonly observed in physiological gait. Our validation shows that model-based estimates of knee joint stiffness coincide well with experimental data obtained using conventional perturbation techniques. We conclude that knee stiffness can be accurately estimated in isometric conditions without applying perturbations, which presents an important step towards our ultimate goal of quantifying knee stiffness during gait. PMID:22801482

  3. Evaluating face trustworthiness: a model based approach

    PubMed Central

    Baron, Sean G.; Oosterhof, Nikolaas N.

    2008-01-01

    Judgments of trustworthiness from faces determine basic approach/avoidance responses and approximate the valence evaluation of faces that runs across multiple person judgments. Here, based on trustworthiness judgments and using a computer model for face representation, we built a model for representing face trustworthiness (study 1). Using this model, we generated novel faces with an increased range of trustworthiness and used these faces as stimuli in a functional Magnetic Resonance Imaging study (study 2). Although participants did not engage in explicit evaluation of the faces, the amygdala response changed as a function of face trustworthiness. An area in the right amygdala showed a negative linear response—as the untrustworthiness of faces increased so did the amygdala response. Areas in the left and right putamen, the latter area extended into the anterior insula, showed a similar negative linear response. The response in the left amygdala was quadratic—strongest for faces on both extremes of the trustworthiness dimension. The medial prefrontal cortex and precuneus also showed a quadratic response, but their response was strongest to faces in the middle range of the trustworthiness dimension. PMID:19015102

  4. Evaluating face trustworthiness: a model based approach.

    PubMed

    Todorov, Alexander; Baron, Sean G; Oosterhof, Nikolaas N

    2008-06-01

    Judgments of trustworthiness from faces determine basic approach/avoidance responses and approximate the valence evaluation of faces that runs across multiple person judgments. Here, based on trustworthiness judgments and using a computer model for face representation, we built a model for representing face trustworthiness (study 1). Using this model, we generated novel faces with an increased range of trustworthiness and used these faces as stimuli in a functional Magnetic Resonance Imaging study (study 2). Although participants did not engage in explicit evaluation of the faces, the amygdala response changed as a function of face trustworthiness. An area in the right amygdala showed a negative linear response-as the untrustworthiness of faces increased so did the amygdala response. Areas in the left and right putamen, the latter area extended into the anterior insula, showed a similar negative linear response. The response in the left amygdala was quadratic--strongest for faces on both extremes of the trustworthiness dimension. The medial prefrontal cortex and precuneus also showed a quadratic response, but their response was strongest to faces in the middle range of the trustworthiness dimension. PMID:19015102

  5. Fast Algorithms for Model-Based Diagnosis

    NASA Technical Reports Server (NTRS)

    Fijany, Amir; Barrett, Anthony; Vatan, Farrokh; Mackey, Ryan

    2005-01-01

    Two improved new methods for automated diagnosis of complex engineering systems involve the use of novel algorithms that are more efficient than prior algorithms used for the same purpose. Both the recently developed algorithms and the prior algorithms in question are instances of model-based diagnosis, which is based on exploring the logical inconsistency between an observation and a description of a system to be diagnosed. As engineering systems grow more complex and increasingly autonomous in their functions, the need for automated diagnosis increases concomitantly. In model-based diagnosis, the function of each component and the interconnections among all the components of the system to be diagnosed (for example, see figure) are represented as a logical system, called the system description (SD). Hence, the expected behavior of the system is the set of logical consequences of the SD. Faulty components lead to inconsistency between the observed behaviors of the system and the SD. The task of finding the faulty components (diagnosis) reduces to finding the components, the abnormalities of which could explain all the inconsistencies. Of course, the meaningful solution should be a minimal set of faulty components (called a minimal diagnosis), because the trivial solution, in which all components are assumed to be faulty, always explains all inconsistencies. Although the prior algorithms in question implement powerful methods of diagnosis, they are not practical because they essentially require exhaustive searches among all possible combinations of faulty components and therefore entail the amounts of computation that grow exponentially with the number of components of the system.

  6. The Use of Modeling-Based Text to Improve Students' Modeling Competencies

    ERIC Educational Resources Information Center

    Jong, Jing-Ping; Chiu, Mei-Hung; Chung, Shiao-Lan

    2015-01-01

    This study investigated the effects of a modeling-based text on 10th graders' modeling competencies. Fifteen 10th graders read a researcher-developed modeling-based science text on the ideal gas law that included explicit descriptions and representations of modeling processes (i.e., model selection, model construction, model validation, model…

  7. Gamma-Ray Burst Afterglows as Probes of Environment and Blastwave Physics. 1; Absorption by Host Galaxy Gas and Dust

    NASA Technical Reports Server (NTRS)

    Starling, R. L. C.; Wijers, R. A. M. J.; Wiersema, K.; Rol, E.; Curran, P. A.; Kouveliotou, C.; vanderHorst, A. J.; Heemskerk, M. H. M.

    2006-01-01

    We use a new approach to obtain limits on the absorbing columns towards an initial sample of 10 long Gamma-Ray Bursts observed with BeppoSAX and selected on the basis of their good optical and nIR coverage, from simultaneous fits to nIR, optical and X-ray afterglow data, in count space and including the effects of metallicity. In no cases is a MIV-like ext,inction preferred, when testing MW, LMC and SMC extinction laws. The 2175A bump would in principle be detectable in all these afterglows, but is not present in the data. An SMC-like gas-to-dust ratio or lower value can be ruled out for 4 of the hosts analysed here (assuming Sh4C metallicity and extinction law) whilst the remainder of the sample have too large an error to discriminate. We provide a more accurate estimate of the line-of-sight extinction and improve upon the uncertainties for the majority of the extinction measurements made in previous studies of this sample. We discuss this method to determine extinction values in comparison with the most commonly employed existing methods.

  8. Transition from interpulse to afterglow plasmas driven by repetitive short-pulse microwaves in a multicusp magnetic field

    SciTech Connect

    Pandey, Shail; Sahu, Debaprasad; Bhattacharjee, Sudeep

    2012-08-15

    In the power-off phase, plasmas generated by repetitive short-pulse microwaves in a multicusp magnetic field show a transitive nature from interpulse to afterglow as a function of pulse duration t{sub w} = 20-200 {mu}s. The ionized medium can be driven from a highly non equilibrium to an equilibrium state inside the pulses, thereby dictating the behavior of the plasma in the power-off phase. Compared to afterglows, interpulse plasmas observed for t{sub w} < 50 {mu}s are characterized by a quasi-steady-state in electron density that persists for {approx} 20-40 {mu}s even after the end of the pulse and has a relatively slower decay rate ({approx} 4.3 Multiplication-Sign 10{sup 4} s{sup -1}) of the electron temperature, as corroborated by optical measurements. The associated electron energy probability function indicates depletion in low energy electrons which appear at higher energies just after the end of the pulse. The transition occurs at t{sub w} {approx} 50 {mu}s as confirmed by time evolution of integrated electron numbers densities obtained from the distribution function.

  9. Luminescence properties of a new green afterglow phosphor NaBaScSi2O7:Eu(2+).

    PubMed

    Li, Gen; Wang, Yuhua; Zeng, Wei; Chen, Wenbo; Han, Shaochun; Guo, Haijie; Wang, Xicheng

    2015-10-28

    A novel green afterglow phosphor NaBaScSi2O7:Eu(2+) was prepared by a solid state reaction under a reductive atmosphere. The NaBaScSi2O7:Eu(2+) phosphor shows two emission bands centered at about 424 (weak) and 502 nm (strong) due to the substitution of Eu(2+) in both Ba(+) and Na(2+) sites, and energy transfer from EuBa (424 nm) to EuNa (502 nm) was found. Both EuBa and EuNa contribute to the afterglow process while EuNa dominates. Na0.99BaScSi2O7:0.01Eu(2+) exhibits green long lasting phosphorescence, whose duration is more than 1 h. The thermoluminescence properties of NaBaScSi2O7:Eu(2+) and the relationship between thermoluminescence and thermal quenching properties were discussed in detail. This work provides a new and efficient candidate for long lasting phosphorescence materials. PMID:26391314

  10. Prototype-based models in machine learning.

    PubMed

    Biehl, Michael; Hammer, Barbara; Villmann, Thomas

    2016-01-01

    An overview is given of prototype-based models in machine learning. In this framework, observations, i.e., data, are stored in terms of typical representatives. Together with a suitable measure of similarity, the systems can be employed in the context of unsupervised and supervised analysis of potentially high-dimensional, complex datasets. We discuss basic schemes of competitive vector quantization as well as the so-called neural gas approach and Kohonen's topology-preserving self-organizing map. Supervised learning in prototype systems is exemplified in terms of learning vector quantization. Most frequently, the familiar Euclidean distance serves as a dissimilarity measure. We present extensions of the framework to nonstandard measures and give an introduction to the use of adaptive distances in relevance learning.

  11. Model-based reconfiguration: Diagnosis and recovery

    NASA Technical Reports Server (NTRS)

    Crow, Judy; Rushby, John

    1994-01-01

    We extend Reiter's general theory of model-based diagnosis to a theory of fault detection, identification, and reconfiguration (FDIR). The generality of Reiter's theory readily supports an extension in which the problem of reconfiguration is viewed as a close analog of the problem of diagnosis. Using a reconfiguration predicate 'rcfg' analogous to the abnormality predicate 'ab,' we derive a strategy for reconfiguration by transforming the corresponding strategy for diagnosis. There are two obvious benefits of this approach: algorithms for diagnosis can be exploited as algorithms for reconfiguration and we have a theoretical framework for an integrated approach to FDIR. As a first step toward realizing these benefits we show that a class of diagnosis engines can be used for reconfiguration and we discuss algorithms for integrated FDIR. We argue that integrating recovery and diagnosis is an essential next step if this technology is to be useful for practical applications.

  12. Towards a Model Based Electronic Nursing Record

    PubMed Central

    Jansen, Niels; Bekkering, Tino; Ruber, Alexander; Gooskens, Erik; Goossen, William T.F.

    2012-01-01

    The electronic nursing record (ENR) as part of the larger electronic health record has been discussed for years. Its implementation is not that widespread as often considered. E.g. in the Netherlands, a fraction of hospitals uses it. This paper describes a nurse led project in a Dutch hospital where an electronic nursing record system has been defined, based on requirements analysis, standardization through Detail Clinical Models (DCM), and implementation. Standardization of data with DCM is a method and a format to organize clinical knowledge, concepts, and data elements such that managing and exchanging semantics of data is independent from specific technology. 28 DCM are used in the specifications of the ENR. Using the DCM standards approach and the mapping of data elements to professional terminologies enable a vendor to develop what is needed for quality care, rather then sell a fixed set product. PMID:24199083

  13. Overarching framework for data-based modelling

    NASA Astrophysics Data System (ADS)

    Schelter, Björn; Mader, Malenka; Mader, Wolfgang; Sommerlade, Linda; Platt, Bettina; Lai, Ying-Cheng; Grebogi, Celso; Thiel, Marco

    2014-02-01

    One of the main modelling paradigms for complex physical systems are networks. When estimating the network structure from measured signals, typically several assumptions such as stationarity are made in the estimation process. Violating these assumptions renders standard analysis techniques fruitless. We here propose a framework to estimate the network structure from measurements of arbitrary non-linear, non-stationary, stochastic processes. To this end, we propose a rigorous mathematical theory that underlies this framework. Based on this theory, we present a highly efficient algorithm and the corresponding statistics that are immediately sensibly applicable to measured signals. We demonstrate its performance in a simulation study. In experiments of transitions between vigilance stages in rodents, we infer small network structures with complex, time-dependent interactions; this suggests biomarkers for such transitions, the key to understand and diagnose numerous diseases such as dementia. We argue that the suggested framework combines features that other approaches followed so far lack.

  14. COASTING EXTERNAL SHOCK IN WIND MEDIUM: AN ORIGIN FOR THE X-RAY PLATEAU DECAY COMPONENT IN SWIFT GAMMA-RAY BURST AFTERGLOWS

    SciTech Connect

    Shen Rongfeng; Matzner, Christopher D. E-mail: matzner@astro.utoronto.ca

    2012-01-01

    The plateaus observed in about one half of the early X-ray afterglows are the most puzzling feature in gamma-ray bursts (GRBs) detected by Swift. By analyzing the temporal and spectral indices of a large X-ray plateau sample, we find that 55% can be explained by external, forward shock synchrotron emission produced by a relativistic ejecta coasting in a {rho}{proportional_to}r{sup -2}, wind-like medium; no energy injection into the shock is needed. After the ejecta collects enough medium and transitions to the adiabatic, decelerating blast wave phase, it produces the post-plateau decay. For those bursts consistent with this model, we find an upper limit for the initial Lorentz factor of the ejecta, {Gamma}{sub 0} {<=} 46({epsilon}{sub e}/0.1){sup -0.24}({epsilon}{sub B}/0.01){sup 0.17}; the isotropic equivalent total ejecta energy is E{sub iso} {approx} 10{sup 53}({epsilon}{sub e}/0.1){sup -1.3}({epsilon}{sub B}/0.01){sup -0.09}(t{sub b} /10{sup 4} s) erg, where {epsilon}{sub e} and {epsilon}{sub B} are the fractions of the total energy at the shock downstream that are carried by electrons and the magnetic field, respectively, and t{sub b} is the end of the plateau. Our finding supports Wolf-Rayet stars as the progenitor stars of some GRBs. It raises intriguing questions about the origin of an intermediate-{Gamma}{sub 0} ejecta, which we speculate is connected to the GRB jet emergence from its host star. For the remaining 45% of the sample, the post-plateau decline is too rapid to be explained in the coasting-in-wind model, and energy injection appears to be required.

  15. Validating agent based models through virtual worlds.

    SciTech Connect

    Lakkaraju, Kiran; Whetzel, Jonathan H.; Lee, Jina; Bier, Asmeret Brooke; Cardona-Rivera, Rogelio E.; Bernstein, Jeremy Ray Rhythm

    2014-01-01

    As the US continues its vigilance against distributed, embedded threats, understanding the political and social structure of these groups becomes paramount for predicting and dis- rupting their attacks. Agent-based models (ABMs) serve as a powerful tool to study these groups. While the popularity of social network tools (e.g., Facebook, Twitter) has provided extensive communication data, there is a lack of ne-grained behavioral data with which to inform and validate existing ABMs. Virtual worlds, in particular massively multiplayer online games (MMOG), where large numbers of people interact within a complex environ- ment for long periods of time provide an alternative source of data. These environments provide a rich social environment where players engage in a variety of activities observed between real-world groups: collaborating and/or competing with other groups, conducting battles for scarce resources, and trading in a market economy. Strategies employed by player groups surprisingly re ect those seen in present-day con icts, where players use diplomacy or espionage as their means for accomplishing their goals. In this project, we propose to address the need for ne-grained behavioral data by acquiring and analyzing game data a commercial MMOG, referred to within this report as Game X. The goals of this research were: (1) devising toolsets for analyzing virtual world data to better inform the rules that govern a social ABM and (2) exploring how virtual worlds could serve as a source of data to validate ABMs established for analogous real-world phenomena. During this research, we studied certain patterns of group behavior to compliment social modeling e orts where a signi cant lack of detailed examples of observed phenomena exists. This report outlines our work examining group behaviors that underly what we have termed the Expression-To-Action (E2A) problem: determining the changes in social contact that lead individuals/groups to engage in a particular behavior

  16. A new model-based RSA method validated using CAD models and models from reversed engineering.

    PubMed

    Kaptein, B L; Valstar, E R; Stoel, B C; Rozing, P M; Reiber, J H C

    2003-06-01

    Roentgen stereophotogrammetric analysis (RSA) was developed to measure micromotion of an orthopaedic implant with respect to its surrounding bone. A disadvantage of conventional RSA is that it requires the implant to be marked with tantalum beads. This disadvantage can potentially be resolved with model-based RSA, whereby a 3D model of the implant is used for matching with the actual images and the assessment of position and rotation of the implant. In this study, a model-based RSA algorithm is presented and validated in phantom experiments. To investigate the influence of the accuracy of the implant models that were used for model-based RSA, we studied both computer aided design (CAD) models as well as models obtained by means of reversed engineering (RE) of the actual implant. The results demonstrate that the RE models provide more accurate results than the CAD models. If these RE models are derived from the very same implant, it is possible to achieve a maximum standard deviation of the error in the migration calculation of 0.06 mm for translations in x- and y-direction and 0.14 mm for the out of plane z-direction, respectively. For rotations about the y-axis, the standard deviation was about 0.1 degrees and for rotations about the x- and z-axis 0.05 degrees. Studies with clinical RSA-radiographs must prove that these results can also be reached in a clinical setting, making model-based RSA a possible alternative for marker-based RSA.

  17. Embedding Task-Based Neural Models into a Connectome-Based Model of the Cerebral Cortex

    PubMed Central

    Ulloa, Antonio; Horwitz, Barry

    2016-01-01

    A number of recent efforts have used large-scale, biologically realistic, neural models to help understand the neural basis for the patterns o