3,562 research outputs found
Identifying Compact Symmetric Objects in the Southern Sky
We present results of multifrequency polarimetric VLBA observations of 20
compact radio sources. The observations represent the northern and southern
extensions of a large survey undertaken to identify Compact Symmetric Objects
(CSOs) Observed in the Northern Sky (COINS). CSOs are young radio galaxies
whose jet axes lie close to the plane of the sky, and whose appearance is
therefore not dominated by relativistic beaming effects. The small linear sizes
of CSOs make them valuable for studies of both the evolution of radio galaxies
and testing unified schemes for active galactic nuclei (AGN). In this paper we
report on observations made of 20 new CSO candidates discovered in the northern
and southern extremities of the VLBA Calibrator Survey. We identify 4 new CSOs,
and discard 12 core-jet sources. The remaining 4 sources remain candidates
pending further investigation. We present continuum images at 5 GHz and 15 GHz
and, where relevant, images of the polarized flux density and spectral index
distributions for the 8 new CSOs and CSO candidates.Comment: accepted to Ap
Thinking beyond the hybrid:“actually-existing” cities “after neoliberalism” in Boyle <i>et al.</i>
In their article, ‘The spatialities of actually existing neoliberalism in Glasgow, 1977 to present’, Mark Boyle, Christopher McWilliams and Gareth Rice (2008) usefully problematise our current understanding of neoliberal urbanism. Our response is aimed at developing a sympathetic but critical approach to Boyle et al's understanding of neoliberal urbanism as illustrated by the Glasgow example. In particular, the counterposing by Boyle et al of a 'hybrid, mutant' model to a 'pure' model of neoliberalism for us misrepresents existing models of neoliberalism as a perfectly finished object rather than a roughly mottled process. That they do not identify any ‘pure’ model leads them to create a straw construct against which they can claim a more sophisticated, refined approach to the messiness of neoliberal urbanism. In contrast, we view neoliberalism as a contested and unstable response to accumulation crises at various scales of analysis
A Compact Supermassive Binary Black Hole System
We report on the discovery of a supermassive binary black hole system in the
radio galaxy 0402+379, with a projected separation between the two black holes
of just 7.3 pc. This is the closest black hole pair yet found by more than two
orders of magnitude. These results are based upon recent multi-frequency
observations using the Very Long Baseline Array (VLBA) which reveal two
compact, variable, flat-spectrum, active nuclei within the elliptical host
galaxy of 0402+379. Multi-epoch observations from the VLBA also provide
constraints on the total mass and dynamics of the system. Low spectral
resolution spectroscopy using the Hobby-Eberly Telescope indicates two velocity
systems with a combined mass of the two black holes of ~1.5 x 10^8 solar
masses. The two nuclei appear stationary while the jets emanating from the
weaker of the two nuclei appear to move out and terminate in bright hot spots.
The discovery of this system has implications for the number of close binary
black holes that might be sources of gravitational radiation. Green Bank
Telescope observations at 22 GHz to search for water masers in this interesting
system are also presented.Comment: 34 pages, 7 figures, Accepted to The Astrophysical Journa
X-ray emission from massive stars in Cyg OB2
We report on the analysis of the Chandra-ACIS data of O, B and WR stars in
the young association Cyg OB2. X-ray spectra of 49 O-stars, 54 B-stars and 3
WR-stars are analyzed and for the brighter sources, the epoch dependence of the
X-ray fluxes is investigated. The O-stars in Cyg\,OB2 follow a well-defined
scaling relation between their X-ray and bolometric luminosities: log(Lx/Lbol)
= -7.2 +/- 0.2. This relation is in excellent agreement with the one previously
derived for the Carina OB1 association. Except for the brightest O-star
binaries, there is no general X-ray overluminosity due to colliding winds in
O-star binaries. Roughly half of the known B-stars in the surveyed field are
detected, but they fail to display a clear relationship between Lx and Lbol.
Out of the three WR stars in Cyg OB2, probably only WR144 is itself responsible
for the observed level of X-ray emission, at a very low log(Lx/Lbol) = -8.8 +/-
0.2. The X-ray emission of the other two WR-stars (WR145 and 146) is most
probably due to their O-type companion along with a moderate contribution from
a wind-wind interaction zone.Comment: Accepted for an ApJS Special Issue devoted to the Chandra Cygnus OB2
Legacy Surve
Observation of Muon Neutrino Disappearance with the MINOS Detectors in the NuMI Neutrino Beam
This Letter reports results from the MINOS experiment based on its initial exposure to neutrinos from the Fermilab NuMI beam. The rates and energy spectra of charged current ν_μ interactions are compared in two detectors located along the beam axis at distances of 1 and 735 km. With 1.27×10^(20) 120 GeV protons incident on the NuMI target, 215 events with energies below 30 GeV are observed at the Far Detector, compared to an expectation of 336±14 events. The data are consistent with ν_μ disappearance via oscillations with Δm_(32)^2|=2.74_(-0.26)^(+0.44)×10^(-3) eV^2 and sin^2(2θ_(23))>0.87 (68% C.L.)
First observations of separated atmospheric ν_μ and ν̅ _μ events in the MINOS detector
The complete 5.4 kton MINOS far detector has been taking data since the beginning of August 2003 at a
depth of 2070 meters water-equivalent in the Soudan mine, Minnesota. This paper presents the first
MINOS observations of ν_μ and ν̅ _μ charged-current atmospheric neutrino interactions based on an
exposure of 418 days. The ratio of upward- to downward-going events in the data is compared to the
Monte Carlo expectation in the absence of neutrino oscillations, giving R^(data)_(up/down/R^(MC)_(up/down) =
0:62^(+0.19)_(0:14)(stat.) ± 0.02(sys.). An extended maximum likelihood analysis of the observed L/E distributions
excludes the null hypothesis of no neutrino oscillations at the 98% confidence level. Using the curvature of
the observed muons in the 1.3 T MINOS magnetic field ν_μ and ν̅ _μ interactions are separated. The ratio of
ν̅ _μ to ν_μ events in the data is compared to the Monte Carlo expectation assuming neutrinos and
antineutrinos oscillate in the same manner, giving R^(data)_(ν_μ/ν̅ _μ) / R^(MC)_(ν_μ/ν̅ _μ) = 0.96^(+0:38)_(0.27)(stat.) ± 0.15(sys.), where
the errors are the statistical and systematic uncertainties. Although the statistics are limited, this is the first
direct observation of atmospheric neutrino interactions separately for ν_μ and ν̅ _μ
J16021+3326: New Multi-Frequency Observations of a Complex Source
We present multifrequency Very Long Baseline Array (VLBA) observations of
J16021+3326. These observations, along with variability data obtained from the
Owens Valley Radio Observatory (OVRO) candidate gamma-ray blazar monitoring
program, clearly indicate this source is a blazar. The peculiar characteristic
of this blazar, which daunted previous classification attempts, is that we
appear to be observing down a precessing jet, the mean orientation of which is
aligned with us almost exactly.Comment: 16 pages, 7 Figures, 2 Tables, accepted to Ap
Observations of HI Absorbing Gas in Compact Radio Sources at Cosmological Redshifts
We present an overview of the occurrence and properties of atomic gas
associated with compact radio sources at redshifts up to z=0.85. Searches for
HI 21cm absorption were made with the Westerbork Synthesis Radio Telescope at
UHF-high frequencies (725-1200 MHz). Detections were obtained for 19 of the 57
sources with usable spectra (33%). We have found a large range in line depths,
from tau=0.16 to tau<=0.001. There is a substantial variety of line profiles,
including Gaussians of less than 10km/s, to more typically 150km/s, as well as
irregular and multi-peaked absorption profiles, sometimes spanning several
hundred km/s. Assuming uniform coverage of the entire radio source, we obtain
column depths of atomic gas between 1e19 and 3.3e21(Tsp/100K)(1/f)cm^(-2).
There is evidence for significant gas motions, but in contrast to earlier
results at low redshift, there are many sources in which the HI velocity is
substantially negative (up to v=-1420km/s) with respect to the optical
redshift, suggesting that in these sources the atomic gas, rather than falling
into the centre, may be be flowing out, interacting with the jets, or rotating
around the nucleus.Comment: 10 pages, accepted for publication in A&
Observatory's linguistic landscape: semiotic appropriation and the reinvention of space
Using a longitudinal ethnographic study of the linguistic landscape (LL) in
Observatory's business corridor of Lower Main Road, the paper explores changes
brought about by the influx of immigrant Africans, their artefacts and language
practices. The paper uses the changes in the LL over time and the development of an
"African Corner" within Lower Main Road, to illustrate the appropriation of space and
the unpredictability, which comes along with highly mobile, technological and
multicultural citizens. It is argued that changes in the LL are part of the act of claiming
and appropriating space wherein space becomes summarily recontexualized and hence
reinvented and "owned" by new actors. It is also argued that space ownership can be
concealed through what we have called "brand anonymity" strategies in which the
identity of the owner is deliberately concealed behind global brands. We conclude that
space is pliable and mobile, and that, it is the people within space who carve out new
social practices in their appropriated space.IBS
- …