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Plasma Suppression of Large Scale Structure Formation in the Universe

Description: We point out that during the reionization epoch of the cosmic history, the plasma collective effect among the ordinary matter would suppress the large scale structure formation. The imperfect Debye shielding at finite temperature would induce a residual long-range electrostatic potential which, working together with the baryon thermal pressure, would counter the gravitational collapse. As a result the effective Jean's length, {tilde {lambda}}{sub J}, is increased by a factor, {tilde {lambda}}{s… more
Date: December 10, 2007
Creator: Chen, Pisin & Lai, Kwang-Chang
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Partner: UNT Libraries Government Documents Department
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Parametrization and Classification of 20 Billion LSST Objects: Lessons from SDSS

Description: The Large Synoptic Survey Telescope (LSST) will be a large, wide-field ground-based system designed to obtain, starting in 2015, multiple images of the sky that is visible from Cerro Pachon in Northern Chile. About 90% of the observing time will be devoted to a deep-wide-fast survey mode which will observe a 20,000 deg{sup 2} region about 1000 times during the anticipated 10 years of operations (distributed over six bands, ugrizy). Each 30-second long visit will deliver 5{sigma} depth for point… more
Date: November 10, 2011
Creator: Ivezic, Z.; /Washington U., Seattle, Astron. Dept.; Axelrod, T.; /Large Binocular Telescope, Tucson; Becker, A. C.; /Washington U., Seattle, Astron. Dept. et al.
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Consistency Test of Dark Energy Models

Description: No Description Available.
Date: July 10, 2013
Creator: Chen, Chien-Wen.; /Taiwan, Natl. Taiwan U.; Gu, Je-An.; /Taiwan, Natl. Taiwan U.; Chen, Pisin. & /KIPAC, Menlo Park /Taiwan, Natl. Taiwan U. /Taipei, Inst. Astron. Astrophys.
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Exploring the Outer Solar System with the ESSENCE Supernova Survey

Description: We report the discovery and orbital determination of 14 trans-Neptunian objects (TNOs) from the ESSENCE Supernova Survey difference imaging data set. Two additional objects discovered in a similar search of the SDSS-II Supernova Survey database were recovered in this effort. ESSENCE repeatedly observed fields far from the solar system ecliptic (-21{sup o} < {beta} < -5{sup o}), reaching limiting magnitudes per observation of I {approx} 23.1 and R {approx} 23.7. We examine several of the n… more
Date: November 10, 2011
Creator: Becker, A. C.; Arraki, K.; Kaib, N. A.; Wood-Vasey, W. M.; Aguilera, C.; Blackman, J. W. et al.
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Partner: UNT Libraries Government Documents Department
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X-Ray Observations of Unidentified H.E.S.S. Gamma-Ray Sources

Description: In a survey of the inner part of the Galaxy, performed with the H.E.S.S. Instrument (High energy stereoscopic system) in 2004 and 2005, a large number of new unidentified very high energy (VHE) {gamma}-ray sources above an energy of 100 GeV was discovered. Often the {gamma}-ray spectra in these sources reach energies of up to {approx} 10 TeV. These are the highest energy particles ever attributed to single astrophysical objects. While a few of these sources can be identified at other wavebands,… more
Date: October 10, 2007
Creator: Funk, S.
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Partner: UNT Libraries Government Documents Department
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GLAST and Ground-Based Gamma-Ray Astronomy

Description: The launch of the Gamma-ray Large Area Space Telescope (GLAST) in 2007 will open the possibility of combined studies of astrophysical sources with existing ground-based VHE {gamma}-ray experiments such as H.E.S.S., VERITAS and MAGIC. Ground-based {gamma}-ray observatories provide complementary capabilities for spectral, temporal, spatial and population studies of high-energy {gamma}-ray sources. Joint observations cover a huge energy range, from 20 MeV to over 50 TeV. The LAT will survey the en… more
Date: October 10, 2007
Creator: Funk, S.; Carson, J. E.; Giebels, B.; Longo, F.; McEnery, J. E.; Paneque, D. et al.
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Partner: UNT Libraries Government Documents Department
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Pulsar Electrodynamics: a Time-dependent View

Description: Pulsar spindown forms a reliable yet enigmatic prototype for the energy loss processes in many astrophysical objects including accretion disks and back holes. In this paper we review the physics of pulsar magnetospheres, concentrating on recent developments in force-free modeling of the magnetospheric structure. In particular, we discuss a new method for solving the equations of time-dependent force-free relativistic MHD in application to pulsars. This method allows to dynamically study the for… more
Date: April 10, 2006
Creator: Spitkovsky, Anatoly
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Partner: UNT Libraries Government Documents Department
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Future GLAST Observations of SNRs and PWNe

Description: Shell-type Supernova remnants (SNRs) have long been known to harbor a population of ultra-relativistic particles, accelerated in the Supernova shock wave by the mechanism of Diffusive shock acceleration. Pulsar Wind Nebulae (PWNe) - diffuse structures surrounding young pulsars - are also known to be a site of particle acceleration in the Galaxy. {gamma}-rays above 100 MeV provide a direct access to acceleration processes through the following channels: ultra-relativistic electrons emit {gamma}-… more
Date: October 10, 2007
Creator: Funk, S.
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Partner: UNT Libraries Government Documents Department
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Time-dependent Force-free Pulsar Magnetospheres: Axisymmetric and Oblique Rotators

Description: Magnetospheres of many astrophysical objects can be accurately described by the low-inertia (or ''force-free'') limit of MHD. We present a new numerical method for solution of equations of force-free relativistic MHD based on the finite-difference time-domain (FDTD) approach with a prescription for handling spontaneous formation of current sheets. We use this method to study the time-dependent evolution of pulsar magnetospheres in both aligned and oblique magnetic geometries. For the aligned ro… more
Date: April 10, 2006
Creator: Spitkovsky, Anatoly
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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High Resolution Imaging of the Anomalous Flux-Ratio Gravitational Lens System CLASS B2045+265: Dark Or Luminous Satellites?

Description: The existence of flux-ratio anomalies between fold and cusp images in galaxy-scale strong-lens systems has led to an interpretation based on the presence of a high mass-fraction of cold-dark-matter (CDM) substructures around galaxies, as predicted by numerical N-body simulations. These substructures can cause large perturbations of the image magnifications, leading to changes in the image flux ratios. The flux-ratio anomaly is particularly evident in the radio-loud quadruple gravitational lens … more
Date: November 10, 2006
Creator: McKean, J. P.; Koopmans, L. V. E.; Flack, C. E.; Fassnacht, C. D.; Thompson, D.; Matthews, K. et al.
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Partner: UNT Libraries Government Documents Department
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The First Generation of Stars in Lambda-CDM Cosmology

Description: We have performed a large set of high-resolution cosmological simulations using smoothed particle hydrodynamics (SPH) to study the formation of the first luminous objects in the {Lambda}CDM cosmology. We follow the collapse of primordial gas clouds in eight early structures and document the scatter in the properties of the first star-forming clouds. Our first objects span formation redshifts from z {approx} 10 to z {approx} 50 and cover an order of magnitude in halo mass. We find that the physi… more
Date: October 10, 2006
Creator: Gao, Liang; Abel, T.; Frenk, C. S.; Jenkins, A.; Springel, V. & Yoshida, N.
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Partner: UNT Libraries Government Documents Department
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Computational Eulerian Hydrodynamics and Galilean Invariance

Description: Eulerian hydrodynamical simulations are a powerful and popular tool for modeling fluids in astrophysical systems. In this work, we critically examine recent claims that these methods violate Galilean invariance of the Euler equations. We demonstrate that Eulerian hydrohynamics methods do converge to a Galilean-invariant solution,provided a well-defined convergent solutions exists. Specifically, we show that numerical diffusion, resulting from diffusion-like terms in the discretized hydrodynamic… more
Date: July 10, 2013
Creator: Robertson, Brant E.; Kravtsov, Andrey V.; /Chicago U., KICP /Chicago U., Astron. Astrophys. Ctr.; Gnedin, Nickolay Y.; /Chicago U., KICP /Fermilab; Abel, Tom et al.
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Partner: UNT Libraries Government Documents Department
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Modern Statistical Methods for GLAST Event Analysis

Description: We describe a statistical reconstruction methodology for the GLAST LAT. The methodology incorporates in detail the statistics of the interactions of photons and charged particles with the tungsten layers in the LAT, and uses the scattering distributions to compute the full probability distribution over the energy and direction of the incident photons. It uses model selection methods to estimate the probabilities of the possible geometrical configurations of the particles produced in the detecto… more
Date: April 10, 2007
Creator: Morris, Robin D.; /RIACS, Mtn. View; Cohen-Tanugi, Johann & /SLAC /KIPAC, Menlo Park
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Partner: UNT Libraries Government Documents Department
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Simulations of Relativistic Collisionless Shocks: Shock Structure and Particle Acceleration

Description: We discuss 3D simulations of relativistic collisionless shocks in electron-positron pair plasmas using the particle-in-cell (PIC) method. The shock structure is mainly controlled by the shock's magnetization (''sigma'' parameter). We demonstrate how the structure of the shock varies as a function of sigma for perpendicular shocks. At low magnetizations the shock is mediated mainly by the Weibel instability which generates transient magnetic fields that can exceed the initial field. At larger ma… more
Date: April 10, 2006
Creator: Spitkovsky, Anatoly
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Partner: UNT Libraries Government Documents Department
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Evidence for the Importance of Resonance Scattering in X-Ray Emission Line Profiles of the O Star Zeta Puppis

Description: We fit the Doppler profiles of the He-like triplet complexes of O VII and N VI in the X-ray spectrum of the O star {zeta} Pup, using XMM-Newton RGS data collected over {approx} 400 ks of exposure. We find that they cannot be well fit if the resonance and intercombination lines are constrained to have the same profile shape. However, a significantly better fit is achieved with a model incorporating the effects of resonance scattering, which causes the resonance line to become more symmetric than… more
Date: October 10, 2006
Creator: Leutenegger, M.A.; U., /Columbia; Owocki, S.P.; Inst., /Bartol Research; Kahn, S.M.; /KIPAC, Menlo Park et al.
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Partner: UNT Libraries Government Documents Department
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The Relation Between Accretion Rate And Jet Power in X-Ray Luminous Elliptical Galaxies

Description: Using Chandra X-ray observations of nine nearby, X-ray luminous elliptical galaxies with good optical velocity dispersion measurements, we show that a tight correlation exists between the Bondi accretion rates calculated from the observed gas temperature and density profiles and estimated black hole masses, and the power emerging from these systems in relativistic jets. The jet powers, which are inferred from the energies and timescales required to inflate cavities observed in the surrounding X… more
Date: March 10, 2006
Creator: Allen, Steven W.; Dunn, R. J. H.; Fabian, A. C.; Taylor, G. B. & Reynolds, C. S.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Magnetic Fields in the Center of the Perseus Cluster

Description: We present Very Long Baseline Array (VLBA) observations of the nucleus of NGC1275, the central, dominant galaxy in the Perseus cluster of galaxies. These are the first observations to resolve the linearly polarized emission from 3C84, and from them we determine a Faraday rotation measure (RM) ranging from 6500 to 7500 rad m{sup -2} across the tip of the bright southern jet component. At 22 GHz some polarization is also detected from the central parsec of 3C84, indicating the presence of even mo… more
Date: March 10, 2006
Creator: Taylor, G. B.; Gugliucci, N. E.; Fabian, A. C.; Sanders, J. S.; Gentile, Gianfranco; Allen, S. W. et al.
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Partner: UNT Libraries Government Documents Department
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High Energy Neutrinos and Cosmic-Rays From Low-Luminosity Gamma-Ray Bursts?

Description: The recently discovered gamma-ray burst (GRB) 060218/SN 2006aj is classified as an X-ray Flash with very long duration driven possibly by a neutron star. Since GRB 060218 is very near {approx} 140 Mpc and very dim, one-year observation by Swift suggests that the true rate of GRB 060218-like events might be very high so that such low luminosity GRBs (LL-GRBs) might form a different population of GRBs from the cosmological high luminosity GRBs (HL-GRBs). We found that the high energy neutrino bac… more
Date: July 10, 2006
Creator: Murase, Kohta; /Kyoto U., Yukawa Inst., Kyoto; Ioka, Kunihito; U., /Kyoto; Nagataki, Shigehiro; /Kyoto U., Yukawa Inst., Kyoto /KIPAC, Menlo Park et al.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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