Ex) Article Title, Author, Keywords
pISSN 0374-4884
eISSN 1976-8524
Articles
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2010-09-15
GRB 090423 at Redshift 8.1: a Theoretical Interpretation
Luca Izzo, Maria Grazia Bernardini, Carlo Luciano Bianco, Letizia Caito, Barbara Patricelli, Remo RuffiniJ. Korean Phy. Soc. 2010; 57(3(1)): 551-556Abstract : GRB 090423 is the farthest GRB ever observed, with a redshift of about 8.1.We present within the Fireshell scenario a complete analysis of this GRB.We model the prompt emission and the first rapid flux decay of the afterglow emission as due to the canonical emission of the interaction, in the interval $0 leq t leq 440$ s, by the accelerated baryonic matter with the CBM.After the data reduction of the Swift data in the BAT (15-150 keV) and XRT (0.2-10 keV) energy bands, we interpret the light curves and the spectral distribution in the context of the Fireshell scenario.We confirm also in this source the existence of a second component, the plateau phase, as responsible for the late emission in the X-ray light curve.This extra component originates from the fact that the ejecta have a range of bulk Lorentz $Gamma$ factor, which starts to interact each other at the start of the plateau phase.
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2010-09-15
Fast detection of the prompt photons from Gamma-ray bursts
Heuijin Lim, S. M. Jeong, J. E. Kim, J. W. NamJ. Korean Phy. Soc. 2010; 57(3(1)): 557-559Abstract : Gamma-ray bursts (GRBs) are the most energetic explosions in the Universe. We present the fast readout system to detect the fast transient events with the wide-field telescope and to manage the huge amount of data from the telescope detector within thelimited processing time.
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2010-09-15
A self-consistent approach to neutron stars
Jorge A. Rueda, M. Rotondo, Remo Ruffini, S.-S. XueJ. Korean Phy. Soc. 2010; 57(3(1)): 560-562Abstract : We present the set of equilibrium equations for a self-gravitating system of degenerate neutrons, protons and electrons in beta equilibrium in the framework of relativistic quantum statistics and the Einstein-Maxwell equations. Special emphasis is given to the crucial role of the constancy of the generalized Fermi energy of particles from which we formulate the general relativistic version of the Thomas-Fermi equation. We discuss briefly the consequences of this approach in the general case of neutron star configurations with a core and a crust.
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2010-09-15
Excursion Set Statistics with Primordial Non-Gaussianity
Graziano Rossi, Pravabati Chingangbam, Changbom ParkJ. Korean Phy. Soc. 2010; 57(3(1)): 563-566Abstract : The statistics of regions above or below a temperature threshold(excursion sets), fully characterized in the contest of Gaussianrandom fields, is here extended to models with primordialnon Gaussianity of the local type, and used to analyzethe Cosmic Microwave Background (CMB) sky via simulated non-Gaussian maps.In particular, it is found that a positive value of the non-Gaussian parameter $f_{m NL}$enhances the number density of the cold CMB excursion sets, along with theirclustering strength, and reduces that of the hot ones. This effect may be important to discriminate between the simplerGaussian hypothesis and non-Gaussian scenarios,arising either from non standard inflation or alternative early-universe models. However, while a distinct signature in the clustering of hot and cold pixels clearly emerges for large non-Gaussianity, particularly at angularscales of about 75 arcmin, the considered statistics appears to be less sensitive when $f_{m NL}$ is relatively small and an additional smoothing isapplied. This fact may pose a challenge if usingthe excursion set regions to constrain $f_{m NL}$, or eitherGaussianity itself, from a real data-set -- in presence of noise andother observational artifacts.
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2010-09-15
Refining trapped surfaces
Sean A. HaywardJ. Korean Phy. Soc. 2010; 57(3(1)): 567-570Abstract : Various refinements of trapped surfaces, intended to apply near the outer horizon of a black hole, and their relations are summarized. Assuming the null energy condition, minimal trapped implies outer trapped, which implies increasingly trapped. Variations of these three definitions form an interwoven hierarchy.
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2010-09-15
ON THE EQUILIBRIUM CONFIGURATION OF TWO REISSNER-NORDSTROM OBJECTS AND REPULSIVE GRAVITY
George Alekseev, Vladimir BelinskiJ. Korean Phy. Soc. 2010; 57(3(1)): 571-577Abstract : %The paper represents content of the talk made by one of us (V.Belinski) at 11%Italian-Korean Meeting (Seoul, November 2009). A family of staticasymptotically flat exact solutions for Einstein-Maxwell equations whichdescribe the field of two electrically charged massive objects (the Reissner -Nordstrom sources without any struts or strings between them) in equilibriumis discussed. The equilibrium is possible only when one of the sources is ablack hole and another one is a naked singularity or in the case when bothsources are extreme black holes (Majumdar-Papapetrou situation).It is interesting that for sufficiently short distance between the sourceseven a neutral Schwarzshild black hole can "hang" freely in the field of anaked singularity which seems that this phenomenon arise only due to the nakedsingularity creating repulsive gravity effect. We stress that the repulsivegravity effect is not specifically due the naked singularity, since thereexist a regular matter sources exhibiting the same phenomena. One of suchsources in the form of Nambu-Goto spherically symmetric membrane is described.The point is that the membrane are able to cut out the central nakedsingularity region and at the same time to join in appropriate way theReissner - Nordstrom repulsive region.%PACS numbers: 04.20.Jb, 04.40.Nr%Keywords: Exact solutions, Einstein-Maxwell spacetimes, Reissner--Nordstrom%field, Nambu--Goto membrane.
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2010-09-15
Emergent Universe from Noncommutative Spacetime
Jungjai Lee, Hyun Seok YangJ. Korean Phy. Soc. 2010; 57(3(1)): 578-581Abstract : The Big Bang was the birth of our Universe happened at Planck epoch.It was not an event developed in an already existing space-time.Rather it was the cosmological event simultaneously generatingspace-time as well as all other matter fields. Therefore, in orderto describe the origin of our Universe, it is necessary to have abackground independent theory for quantum gravity where anyspace-time structure is not {it a priori} assumed but defined fromthe theory. The emergent gravity based on noncommutative gaugetheory provides such a background independent formulation of quantumgravity and the emergent space-time leads to a novel picture aboutthe dynamical origin of space-time. We address some issues about theorigin of our Universe and discuss implications to cosmology fromthe emergent gravity.
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2010-09-15
The Geodesic Properties of the Hypercylindrical and Extraordinary Spacetimes
Bogeun Gwak, Bum-hoon Lee, Wonwoo Lee, Hyeong-Chan KimJ. Korean Phy. Soc. 2010; 57(3(1)): 582-585Abstract : {small We study the geodesic properties of the two stationary hypercylindrical spacetimes in (4+1) dimensions, static and extraordinary spacetime. The effective potential analysis and gravitational lensing effects are studied in the static spacetime. The geodesic equation is numerically solved to get the orbits of light and particles, and we focus on the relation between geodesic orbits and precession rate in the extraordinary spacetime. We give the all effective potential and orbits in specific parameter region. This article is prepared for the proceedings of 11th Italian-Korean Workshop on Symposium on Relativistic Astrophysics in Korea, Nov 2009.}
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2010-09-15
Generating spatial curvature in an inhomogeneous universe: A bottom-up approach to cosmology
Kjell Rosquist, Lars SamuelssonJ. Korean Phy. Soc. 2010; 57(3(1)): 586-590Abstract : We take first steps towards a new bottom-up approach to cosmology. The dynamics is described in terms of the world lines of the cosmic grains (galaxies or clusters of galaxies). The description is microscopic in the sense that there is no fluid assumption. The motion of each grain is geodesic ensuring the presence of gravitational interactions only. The scheme is fully general in that there is no restriction to homogeneous or isotropic models. Our approach is mathematically similar to Buchert¡?s averaging method, but there are important di erences. In particular, we use statistical averages, when needed, not volume averages. Forexample, a crucial ingredient in any cosmological framework is the spatial curvature. Here we give an estimate of the scalar curvature based on statistical averages of the actual mass distribution in the universe.
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2010-09-15
Dynamical intersecting brane solutions
Kunihito UzawaJ. Korean Phy. Soc. 2010; 57(3(1)): 591-594Abstract : We present dynamical intersecting brane solutions in higher-dimensional gravitational theory coupled to dilaton and several forms. Assuming the forms of metric, form fields, and dilaton field, we can give the dynamical intersecting brane solutions. The dynamical solutions can be always obtained by replacing the constant modulus $h_0$ in the warp factor for supersymmetric solutions by a linear function $h_0(t)$ of the time coordinates $t$.
February, 2021
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