5,413 research outputs found
Survival analysis of the optical brightness of GRB host galaxies
We studied the unbiased optical brightness distribution which was calculated
from the survival analysis of host galaxies and its relationship with the Swift
GRB data of the host galaxies observed by the Keck telescopes. Based on the
sample obtained from merging the Swift GRB table and the Keck optical data we
also studied the dependence of this distribution on the data of the GRBs.
Finally, we compared the HGs distribution with standard galaxies distribution
which is in the DEEP2 galaxies catalog.Comment: Swift: 10 Years of Discovery. Conference paper. 2-5 December 2014. La
Sapienza University, Rome, Ital
A giant ring-like structure at 0.78<z<0.86 displayed by GRBs
According to the cosmological principle, Universal large-scale structure is
homogeneous and isotropic. The observable Universe, however, shows complex
structures even on very large scales. The recent discoveries of structures
significantly exceeding the transition scale of 370 Mpc pose a challenge to the
cosmological principle.
We report here the discovery of the largest regular formation in the
observable Universe; a ring with a diameter of 1720 Mpc, displayed by 9 gamma
ray bursts (GRBs), exceeding by a factor of five the transition scale to the
homogeneous and isotropic distribution. The ring has a major diameter of
and a minor diameter of at a distance of 2770 Mpc in the 0.78<z<0.86
redshift range, with a probability of of being the result of
a random fluctuation in the GRB count rate.
Evidence suggests that this feature is the projection of a shell onto the
plane of the sky. Voids and string-like formations are common outcomes of
large-scale structure. However, these structures have maximum sizes of 150 Mpc,
which are an order of magnitude smaller than the observed GRB ring diameter.
Evidence in support of the shell interpretation requires that temporal
information of the transient GRBs be included in the analysis.
This ring-shaped feature is large enough to contradict the cosmological
principle. The physical mechanism responsible for causing it is unknown.Comment: Accepted for publication in MNRAS, 13 pages, 8 figures and 4 table
Black Holes in Einstein-Aether Theory
We study black hole solutions in general relativity coupled to a unit
timelike vector field dubbed the "aether". To be causally isolated a black hole
interior must trap matter fields as well as all aether and metric modes. The
theory possesses spin-0, spin-1, and spin-2 modes whose speeds depend on four
coupling coefficients. We find that the full three-parameter family of local
spherically symmetric static solutions is always regular at a metric horizon,
but only a two-parameter subset is regular at a spin-0 horizon. Asymptotic
flatness imposes another condition, leaving a one-parameter family of regular
black holes. These solutions are compared to the Schwarzschild solution using
numerical integration for a special class of coupling coefficients. They are
very close to Schwarzschild outside the horizon for a wide range of couplings,
and have a spacelike singularity inside, but differ inside quantitatively. Some
quantities constructed from the metric and aether oscillate in the interior as
the singularity is approached. The aether is at rest at spatial infinity and
flows into the black hole, but differs significantly from the the 4-velocity of
freely-falling geodesics.Comment: 22 pages, 6 figures; v2: minor editing; v3: corrected overall sign in
twist formula and an error in the equation for the aether stress tensor.
Results unchanged since correct form was used in calculations; v4: corrected
minor typ
Action and Hamiltonian for eternal black holes
We present the Hamiltonian, quasilocal energy, and angular momentum for a
spacetime region spatially bounded by two timelike surfaces. The results are
applied to the particular case of a spacetime representing an eternal black
hole. It is shown that in the case when the boundaries are located in two
different wedges of the Kruskal diagram, the Hamiltonian is of the form , where and are the Hamiltonian functions for the right
and left wedges respectively. The application of the obtained results to the
thermofield dynamics description of quantum effects in black holes is briefly
discussed.Comment: 24 pages, Revtex, 5 figures (available upon request
Spacetimes foliated by Killing horizons
It seems to be expected, that a horizon of a quasi-local type, like a Killing
or an isolated horizon, by analogy with a globally defined event horizon,
should be unique in some open neighborhood in the spacetime, provided the
vacuum Einstein or the Einstein-Maxwell equations are satisfied. The aim of our
paper is to verify whether that intuition is correct. If one can extend a so
called Kundt metric, in such a way that its null, shear-free surfaces have
spherical spacetime sections, the resulting spacetime is foliated by so called
non-expanding horizons. The obstacle is Kundt's constraint induced at the
surfaces by the Einstein or the Einstein-Maxwell equations, and the requirement
that a solution be globally defined on the sphere. We derived a transformation
(reflection) that creates a solution to Kundt's constraint out of data defining
an extremal isolated horizon. Using that transformation, we derived a class of
exact solutions to the Einstein or Einstein-Maxwell equations of very special
properties. Each spacetime we construct is foliated by a family of the Killing
horizons. Moreover, it admits another, transversal Killing horizon. The
intrinsic and extrinsic geometry of the transversal Killing horizon coincides
with the one defined on the event horizon of the extremal Kerr-Newman solution.
However, the Killing horizon in our example admits yet another Killing vector
tangent to and null at it. The geometries of the leaves are given by the
reflection.Comment: LaTeX 2e, 13 page
On the `Stationary Implies Axisymmetric' Theorem for Extremal Black Holes in Higher Dimensions
All known stationary black hole solutions in higher dimensions possess
additional rotational symmetries in addition to the stationary Killing field.
Also, for all known stationary solutions, the event horizon is a Killing
horizon, and the surface gravity is constant. In the case of non-degenerate
horizons (non-extremal black holes), a general theorem was previously
established [gr-qc/0605106] proving that these statements are in fact generally
true under the assumption that the spacetime is analytic, and that the metric
satisfies Einstein's equation. Here, we extend the analysis to the case of
degenerate (extremal) black holes. It is shown that the theorem still holds
true if the vector of angular velocities of the horizon satisfies a certain
"diophantine condition," which holds except for a set of measure zero.Comment: 30pp, Latex, no figure
Calculations of the dynamical critical exponent using the asymptotic series summation method
We consider how the Pad'e-Borel, Pad'e-Borel-Leroy, and conformal mapping
summation methods for asymptotic series can be used to calculate the dynamical
critical exponent for homogeneous and disordered Ising-like systems.Comment: 21 RevTeX pages, 2 figure
Exact Results for a Three-Body Reaction-Diffusion System
A system of particles hopping on a line, singly or as merged pairs, and
annihilating in groups of three on encounters, is solved exactly for certain
symmetrical initial conditions. The functional form of the density is nearly
identical to that found in two-body annihilation, and both systems show
non-mean-field, ~1/t**(1/2) instead of ~1/t, decrease of particle density for
large times.Comment: 10 page
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