3,614 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
Maxwell Fields in Spacetimes Admitting Non-Null Killing Vectors
We consider source-free electromagnetic fields in spacetimes possessing a
non-null Killing vector field, . We assume further that the
electromagnetic field tensor, , is invariant under the action of the
isometry group induced by . It is proved that whenever the two
potentials associated with the electromagnetic field are functionally
independent the entire content of Maxwell's equations is equivalent to the
relation \n^aT_{ab}=0. Since this relation is implied by Einstein's equation
we argue that it is enough to solve merely Einstein's equation for these
electrovac spacetimes because the relevant equations of motion will be
satisfied automatically. It is also shown that for the exceptional case of
functionally related potentials \n^aT_{ab}=0 implies along with one of the
relevant equations of motion that the complementary equation concerning the
electromagnetic field is satisfied.Comment: 7 pages,PACS numbers: 04.20.Cv, 04.20.Me, 04.40.+
Killing spinor data on distorted black hole horizons and the uniqueness of stationary vacuum black holes
We make use of the black hole holograph construction of [I. R\'acz,
Stationary black holes as holographs, Class. Quantum Grav. 31, 035006 (2014)]
to analyse the existence of Killing spinors in the domain of dependence of the
horizons of distorted black holes. In particular, we provide conditions on the
bifurcation sphere ensuring the existence of a Killing spinor. These conditions
can be understood as restrictions on the curvature of the bifurcation sphere
and ensure the existence of an axial Killing vector on the 2-surface. We obtain
the most general 2-dimensional metric on the bifurcation sphere for which these
curvature conditions are satisfied. Remarkably, these conditions are found to
be so restrictive that, in the considered particular case, the free data on the
bifurcation surface (determining a distorted black hole spacetime) is
completely determined by them. In addition, we formulate further conditions on
the bifurcation sphere ensuring that the Killing vector associated to the
Killing spinor is Hermitian. Once the existence of a Hermitian Killing vector
is guaranteed, one can use a characterisation of the Kerr spacetime due to Mars
to identify the particular subfamily of 2-metrics giving rise to a member of
the Kerr family in the black hole holograph construction. Our analysis sheds
light on the role of asymptotic flatness and curvature conditions on the
bifurcation sphere in the context of the problem of uniqueness of stationary
black holes. The Petrov type of the considered distorted black hole spacetimes
is also determined.Comment: 39 pages, 1 figur
A Hyperbolic Solver for Black Hole Initial Data in Numerical Relativity
Initial data in numerical relativity. The constraints are formulated as elliptic equations, parabolic equations and strongly hyperbolic equations. This presentation is about a different approach to initial data for black holes, the strongly hyperbolic method
The clustering of gamma-ray bursts in the Hercules-Corona Borealis Great Wall: the largest structure in the Universe?
The Hercules-Corona Borealis Great Wall is a statistically significant
clustering of gamma-ray bursts around redshift 2. Motivated by recent
theoretical results indicating that a maximal Universal structure size may
indeed coincide with its estimated size (2-3Gpc), we reexamine the question of
this Great Wall's existence from both observational and theoretical
perspectives. Our statistical analyses confirm the clustering's presence in the
most reliable data set currently available, and we present a video showing what
this data set looks like in~3D. Cosmological explanations (i.e. having to do
with the distribution of gravitating matter) and astrophysical explanations
(i.e. having to do with the rate of star formation over cosmic time and space)
regarding the origin of such a structure are presented and briefly discussed
and the role of observational bias is also discussed at length. This, together
with the scientific importance of using gamma-ray bursts as unique cosmological
probes, emphasises the need for future missions such as the THESEUS satellite
which will provide us with unprecedentedly homogeneous data of gamma-ray bursts
with measured redshifts. We conclude from all this that the Hercules-Corona
Borealis Great Wall may indeed be the largest structure in the Universe - but
to be able to decide conclusively whether it actually exists, we need THESEUS.Comment: Accepted for publication in MNRAS. 12 pages, 3 figures, 3 table
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