4,436 research outputs found
On the population of remnant FRII radio galaxies and implications for radio source dynamics
The purpose of this work is two-fold: (1) to quantify the occurrence of
ultra-steep spectrum remnant FRII radio galaxies in a 74 MHz flux limited
sample, and (2) perform Monte-Carlo simulations of the population of active and
remnant FRII radio galaxies to confront models of remnant lobe evolution, and
provide guidance for further investigation of remnant radio galaxies. We find
that fewer than 2 of FRII radio galaxies with S Jy are
candidate ultra-steep spectrum remnants, where we define ultra-steep spectrum
as . Our Monte-Carlo simulations
demonstrate that models involving Sedov-like expansion in the remnant phase,
resulting in rapid adiabatic energy losses, are consistent with this upper
limit, and predict the existence of nearly twice as many remnants with normal
(not ultra-steep) spectra in the observed frequency range as there are
ultra-steep spectrum remnants. This model also predicts an ultra-steep remnant
fraction approaching 10 at redshifts . Importantly, this model
implies the lobes remain over-pressured with respect to the ambient medium well
after their active lifetime, in contrast with existing observational evidence
that many FRII radio galaxy lobes reach pressure equilibrium with the external
medium whilst still in the active phase. The predicted age distribution of
remnants is a steeply decreasing function of age. In other words young remnants
are expected to be much more common than old remnants in flux limited samples.
For this reason, incorporating higher frequency data GHz will be of
great benefit to future studies of the remnant population.Comment: 19 pages, 8 figures, 4 table
A Multi-Wavelength Study of the Jet, Lobes and Core of the Quasar PKS 2101-490
We present a detailed study of the X-ray, optical and radio emission from the
jet, lobes and core of the quasar PKS 2101-490 as revealed by new Chandra, HST
and ATCA images. We extract the radio to X-ray spectral energy distributions
from seven regions of the 13 arcsecond jet, and model the jet X-ray emission in
terms of Doppler beamed inverse Compton scattering of the cosmic microwave
background (IC/CMB) for a jet in a state of equipartition between particle and
magnetic field energy densities. This model implies that the jet remains highly
relativistic hundreds of kpc from the nucleus, with a bulk Lorentz factor Gamma
~ 6 and magnetic field of order 30 microGauss. We detect an apparent radiative
cooling break in the synchrotron spectrum of one of the jet knots, and are able
to interpret this in terms of a standard one-zone continuous injection model,
based on jet parameters derived from the IC/CMB model. However, we note
apparent substructure in the bright optical knot in one of the HST bands. We
confront the IC/CMB model with independent estimates of the jet power, and find
that the IC/CMB model jet power is consistent with the independent estimates,
provided that the minimum electron Lorentz factor gamma_min > 50, and the knots
are significantly longer than the jet width, as implied by de-projection of the
observed knot lengths.Comment: 16 pages, 10 figures, 6 table
The charmonium and bottomonium mass spectroscopy with a simple approximaton of the kinetic term
In this paper we propose a particular description of meson spectroscopy, with
emphasis in heavy bound states like charmonia and bottomonia, after working on
the main aspects of the construction of an effective potential model. We use
the prerogatives from ``soft QCD'' to determine the effective potential terms,
establishing the asymptotic Coulomb term from one gluon exchange approximation.
At the same time, a linear confinement term is introduced in agreement with QCD
and phenomenological prescription. The main aspect of this work is the
simplification in the calculation, consequence of a precise and simplified
description of the kinetic term of the Hamiltonian. With this proposition we
perform the calculations of mass spectroscopy for charmonium and bottomonium
mesons and we discuss the real physical possibilities of developing a
generalized potential model, its possible advantages relative to experimental
parameterization and complexity in numerical calculations
Combining cytotoxicity assessment and Xenopus laevis phenotypic abnormality assay as a predictor of nanomaterial safety
The African clawed frog, Xenopus laevis, has been used as an efficient pre-clinical screening tool to predict drug safety during the early stages of the drug discovery process. X. laevis is a relatively inexpensive model that can be used in whole organism high-throughput assays whilst maintaining a high degree of homology to the higher vertebrate models often used in scientific research. Despite an ever-increasing volume of biomedical nanoparticles (NPs) in development, their unique physico-chemical properties challenge the use of standard toxicology assays. Here, we present a protocol that directly compares the sensitivity of X. laevis development as a tool to assess potential NP toxicity by observation of embryo phenotypic abnormalities/lethality after NP exposure to in vitro cytotoxicity obtained using mammalian cell lines. In combination with conventional cytotoxicity assays, the X. laevis phenotypic assay provides accurate data to efficiently assess the safety of a novel biomedical NP
Discovery of an X-ray Jet and Extended Jet Structure in the Quasar PKS 1055+201
This letter reports rich X-ray jet structures found in the Chandra
observation of PKS 1055+201. In addition to an X-ray jet coincident with the
radio jet we detect a region of extended X-ray emission surrounding the jet as
far from the core as the radio hotspot to the North, and a similar extended
X-ray region along the presumed path of the unseen counterjet to the Southern
radio lobe. Both X-ray regions show a similar curvature to the west, relative
to the quasar. We interpret this as the first example where we separately
detect the X-ray emission from a narrow jet and extended, residual jet plasma
over the entire length of a powerful FRII jet.Comment: Accepted for publication in Ap. J. Letters. 4 pages, 3 figure
The microarcsecond structure of an active galactic nucleus jet via interstellar scintillation
We describe a new tool for studying the structure and physical
characteristics of ultracompact AGN jets and their surroundings with
microarcsecond precision. This tool is based on the frequency dependence of the
light curves observed for intra-day variable radio sources, where the
variability is caused by interstellar scintillation. We apply this method to
PKS1257-326 to resolve the core-shift as a function of frequency on scales well
below ~12 microarcseconds. We find that the frequency dependence of the
position of the scintillating component is r \propto \nu^{-0.1 \pm 0.24} (99%
confidence interval) and the frequency dependence of the size of the
scintillating component is d \propto \nu^{-0.64 \pm 0.006}. Together, these
results imply that the jet opening angle increases with distance along the jet:
d \propto r^{n_d}$ with n_d > 1.8. We show that the flaring of the jet, and
flat frequency dependence of the core position is broadly consistent with a
model in which the jet is hydrostatically confined and traversing a steep
pressure gradient in the confining medium with p \propto r^{-n_p} and n_p > 7.
Such steep pressure gradients have previously been suggested based on VLBI
studies of the frequency dependent core shifts in AGN.Comment: accepted for publication in Ap
Spectrum for Heavy Quankonia and Mixture of the Relevant Wave Functions within the Framework of Bethe-Salpeter Equation
Considering the fact that some excited states of the heavy quarkonia
(charmonium and bottomonium) still missing in experimental observations and
potential applications of the relevant wave functions of the bound states, we
re-analyze the spectrum and the relevant wave functions of the heavy quarkonia
within the framework of Bethe-Salpeter (B.S.) equation with a proper
QCD-inspired kernel. Such a kernel for the heavy quarkonia, relating to
potential of non-relativistic quark model, is instantaneous, so we call the
corresponding B.S. equation as BS-In equation throughout the paper.
Particularly, a new way to solve the B.S. equation, which is different from the
traditional ones, is proposed here, and with it not only the known spectrum for
the heavy quarkonia is re-generated, but also an important issue is brought in,
i.e., the obtained solutions of the equation `automatically' include the
'fine', 'hyperfine' splittings and the wave function mixture, such as
wave mixing in states, wave mixing in
states for charmonium and bottomonium etc. It is pointed out that the best
place to test the wave mixture probably is at -factory ( collider
running at -boson pole with extremely high luminosity).Comment: 26 pages, 8 figure
Very High Angular Resolution Science with the Square Kilometre Array
Preliminary specifications for the Square Kilometre Array (SKA) call for 25%
of the total collecting area of the dish array to be located at distances
greater than 180 km from the core, with a maximum baseline of at least 3000 km.
The array will provide angular resolution ~ 40 - 2 mas at 0.5 - 10 GHz with
image sensitivity reaching < 50 nJy/beam in an 8 hour integration with 500 MHz
bandwidth. Given these specifications, the high angular resolution component of
the SKA will be capable of detecting brightness temperatures < 200 K with
milliarcsecond-scale angular resolution. The aim of this article is to bring
together in one place a discussion of the broad range of new and important high
angular resolution science that will be enabled by the SKA, and in doing so,
address the merits of long baselines as part of the SKA. We highlight the fact
that high angular resolution requiring baselines greater than 1000 km provides
a rich science case with projects from many areas of astrophysics, including
important contributions to key SKA science.Comment: 13 pages, 6 figure
Fine structure splittings of excited P and D states in charmonium
It is shown that the fine structure splittings of the and
excited states in charmonium are as large as those of the state if the
same is used. The predicted mass
GeV appears to be 120 MeV lower that the center of gravity of the
multiplet and lies below the threshold. Our value of
is approximately 80 MeV lower than that from the paper by Godfrey and Isgur
while the differences in the other masses are \la 20 MeV. Relativistic
kinematics plays an important role in our analysis.Comment: 12 page
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