3,332 research outputs found
An Attempt to Probe the Radio Jet Collimation Regions in NGC 4278, NGC 4374 (M84), and NGC 6166
NRAO Very Long Baseline Array (VLBA) observations of NGC 4278, NGC 4374
(M84), NGC 6166, and M87 (NGC 4486) have been made at 43 GHz in an effort to
image the jet collimation region. This is the first attempt to image the first
three sources at 43 GHz using Very Long Baseline Interferometry (VLBI)
techniques. These three sources were chosen because their estimated black hole
mass and distance implied a Schwarzschild radius with large angular size,
giving hope that the jet collimation regions could be studied. Phase
referencing was utilize for the three sources because of their expected low
flux densities. M87 was chosen as the calibrator for NGC 4374 because it
satisfied the phase referencing requirements: nearby to the source and
sufficiently strong. Having observed M87 for a long integration time, we have
detected its sub-parsec jet, allowing us to confirm previous high resolution
observations made by Junor, Biretta & Livio, who have indicated that a wide
opening angle was seen near the base of the jet. Phase referencing successfully
improved our image sensitivity, yielding detections and providing accurate
positions for NGC 4278, NGC 4374 and NGC 6166. These sources are point
dominated, but show suggestions of extended structure in the direction of the
large-scale jets. However, higher sensitivity will be required to study their
sub-parsec jet structure
The IRAS Revised Bright Galaxy Sample (RBGS)
IRAS flux densities, redshifts, and infrared luminosities are reported for
all sources identified in the IRAS Revised Bright Galaxy Sample (RBGS), a
complete flux-limited survey of all extragalactic objects with total 60 micron
flux density greater than 5.24 Jy, covering the entire sky surveyed by IRAS at
Galactic latitude |b| > 5 degrees. The RBGS includes 629 objects, with a median
(mean) sample redshift of 0.0082 (0.0126) and a maximum redshift of 0.0876. The
RBGS supersedes the previous two-part IRAS Bright Galaxy Samples, which were
compiled before the final ("Pass 3") calibration of the IRAS Level 1 Archive in
May 1990. The RBGS also makes use of more accurate and consistent automated
methods to measure the flux of objects with extended emission. Basic properties
of the RBGS sources are summarized, including estimated total infrared
luminosities, as well as updates to cross-identifications with sources from
optical galaxy catalogs established using the NASA/IPAC Extragalactic Database
(NED). In addition, an atlas of images from the Digitized Sky Survey with
overlays of the IRAS position uncertainty ellipse and annotated scale bars is
provided for ease in visualizing the optical morphology in context with the
angular and metric size of each object. The revised bolometric infrared
luminosity function, phi(L_ir), for infrared bright galaxies in the local
Universe remains best fit by a double power law, phi(L_ir) ~ L_ir^alpha, with
alpha = -0.6 (+/- 0.1), and alpha = -2.2 (+/- 0.1) below and above the
"characteristic" infrared luminosity L_ir ~ 10^{10.5} L_solar, respectively.
(Abridged)Comment: Accepted for publication in the Astronomical Journal. Contains 50
pages, 7 tables, 16 figures. Due to astro-ph space limits, only 1 of 26 pages
of Figure 1, and 1 of 11 pages of Table 7, are included; full resolution
Postscript files are available at
http://nedwww.ipac.caltech.edu/level5/March03/IRAS_RBGS/Figures/ .
Replacement: Corrected insertion of Fig. 15 (MethodCodes.ps) in LaTe
Radio Jet-Ambient Medium Interactions on Parsec Scales in the Blazar 1055+018
As part of our study of the magnetic fields of AGN we have recently observed
a large sample of blazars with the Very Long Baseline Array. Here we report the
discovery of a striking two-component jet in the source 1055+018, consisting of
an inner spine with a transverse magnetic field, and a fragmentary but distinct
boundary layer with a longitudinal magnetic field. The polarization
distribution in the spine strongly supports shocked-jet models while that in
the boundary layer suggests interaction with the surrounding medium. This
behavior suggests a new way to understand the differing polarization properties
of strong- and weak-lined blazars.Comment: LaTex; 10 pages; 6 figures; reference fix; to appear in ApJL, 518,
1999 June 2
Reconfigurable controlled two-qubit operation on a quantum photonic chip
Integrated quantum photonics is an appealing platform for quantum information
processing, quantum communication and quantum metrology. In all these
applications it is necessary not only to be able to create and detect Fock
states of light but also to program the photonic circuits that implements some
desired logical operation. Here we demonstrate a reconfigurable controlled
two-qubit operation on a chip using a multiwaveguide interferometer with a
tunable phase shifter. We find excellent agreement between theory and
experiment, with a 0.98 \pm 0.02 average similarity between measured and ideal
operations
PCR for the detection of pathogens in neonatal early onset sepsis.
BACKGROUND: A large proportion of neonates are treated for presumed bacterial sepsis with broad spectrum antibiotics even though their blood cultures subsequently show no growth. This study aimed to investigate PCR-based methods to identify pathogens not detected by conventional culture. METHODS: Whole blood samples of 208 neonates with suspected early onset sepsis were tested using a panel of multiplexed bacterial PCRs targeting Streptococcus pneumoniae, Streptococcus agalactiae (GBS), Staphylococcus aureus, Streptococcus pyogenes (GAS), Enterobacteriaceae, Enterococcus faecalis, Enterococcus faecium, Ureaplasma parvum, Ureaplasma urealyticum, Mycoplasma hominis and Mycoplasma genitalium, a 16S rRNA gene broad-range PCR and a multiplexed PCR for Candida spp. RESULTS: Two-hundred and eight samples were processed. In five of those samples, organisms were detected by conventional culture; all of those were also identified by PCR. PCR detected bacteria in 91 (45%) of the 203 samples that did not show bacterial growth in culture. S. aureus, Enterobacteriaceae and S. pneumoniae were the most frequently detected pathogens. A higher bacterial load detected by PCR was correlated positively with the number of clinical signs at presentation. CONCLUSION: Real-time PCR has the potential to be a valuable additional tool for the diagnosis of neonatal sepsis
The XMM-Newton Detection of Diffuse Inverse Compton X-rays from Lobes of the FR-II Radio Galaxy 3C98
The XMM-Newton observation of the nearby FR-II radio galaxy 3C 98 is
reported. In two exposures on the target, faint diffuse X-ray emission
associated with the radio lobes was significantly detected, together with a
bright X-ray active nucleus, of which the 2 -- 10 keV intrinsic luminosity is
(4 -- 8) \times 10^{42} erg s-1. The EPIC spectra of the northern and southern
lobes are reproduced by a single power law model modified by the Galactic
absorption, with a photon index of 2.2-0.5+0.6 and 1.7-0.6+0.7 respectively.
These indices are consistent with that of the radio synchrotron spectrum, 1.73
+- 0.01 The luminosity of the northern and southern lobes are measured to be
8.3-2.6+3.3 \times 10^{40} erg s-1 and 9.2-4.3+5.7 \times 10^{40} erg s-1,
respectively, in the 0.7 -- 7 keV range. The diffuse X-ray emission is
interpreted as an inverse-Compton emission, produced when the
synchrotron-emitting energetic electrons in the lobes scatter off the cosmic
microwave background photons. The magnetic field in the lobes is calculated to
be about 1.7 \mu G, which is about 2.5 times lower than the value estimated
under the minimum energy condition. The energy density of the electrons is
inferred to exceed that in the magnetic fields by a factor of 40 -- 50.Comment: 23 pages, 7 figures. Accepted for publication in the Astrophysical
Journa
Bumps and rings in a two-dimensional neural field: splitting and rotational instabilities
In this paper we consider instabilities of localised solutions in planar neural field firing rate models of Wilson-Cowan or Amari type. Importantly we show that angular perturbations can destabilise spatially localised solutions. For a scalar model with Heaviside firing rate function we calculate symmetric one-bump and ring solutions explicitly and use an Evans function approach to predict the point of instability and the shapes of the dominant growing modes. Our predictions are shown to be in excellent agreement with direct numerical simulations. Moreover, beyond the instability our simulations demonstrate the emergence of multi-bump and labyrinthine patterns.
With the addition of spike-frequency adaptation, numerical simulations of the resulting vector model show that it is possible for structures without rotational symmetry, and in particular multi-bumps, to undergo an instability to a rotating wave. We use a general argument, valid for smooth firing rate functions, to establish the conditions necessary to generate such a rotational instability. Numerical continuation of the rotating wave is used to quantify the emergent angular velocity as a bifurcation parameter is varied. Wave stability is found via the numerical evaluation of an associated eigenvalue problem
VLBI Polarimetry of 177 Sources from the Caltech-Jodrell Bank Flat-spectrum Survey
We present VLBA observations and a statistical analysis of 5 GHz VLBI
polarimetry data from 177 sources in the Caltech-Jodrell Bank flat-spectrum
(CJF) survey. The CJF survey, a complete, flux-density-limited sample of 293
extragalactic radio sources, gives us the unique opportunity to compare a broad
range of source properties for quasars, galaxies and BL Lacertae objects. We
focus primarily on jet properties, specifically the correlation between the jet
axis angle and the polarization angle in the core and jet. A strong correlation
is found for the electric vector polarization angle in the cores of quasars to
be perpendicular to the jet axis. Contrary to previous claims, no correlation
is found between the jet polarization angle and the jet axis in either quasars
or BL Lac objects. With this large, homogeneous sample we are also able to
investigate cosmological issues and AGN evolution.Comment: Accepted to the Astrophysical Journal: 37 pages, 14 figure
870 micron observations of nearby 3CRR radio galaxies
We present submillimeter continuum observations at 870 microns of the cores
of low redshift 3CRR radio galaxies, observed at the Heinrich Hertz
Submillimeter Telescope. The cores are nearly flat spectrum between the radio
and submillimeter which implies that the submillimeter continuum is likely to
be synchrotron emission and not thermal emission from dust. The emitted power
from nuclei detected at optical wavelengths and in the X-rays is similar in the
submillimeter, optical and X-rays. The submillimeter to optical and X-ray power
ratios suggest that most of these sources resemble misdirected BL Lac type
objects with synchrotron emission peaking at low energies. However we find
three exceptions, the FR I galaxy 3C264 and the FR II galaxies 3C390.3 and
3C338 with high X-ray to submillimeter luminosity ratios. These three objects
are candidate high or intermediate energy peaked BL Lac type objects. With
additional infrared observations and from archival data, we compile spectral
energy distributions (SEDs) for a subset of these objects. The steep dips
observed near the optical wavelengths in many of these objects suggest that
extinction inhibits the detection and reduces the flux of optical continuum
core counterparts. High resolution near or mid-infrared imaging may provide
better measurements of the underlying synchrotron emission peak.Comment: accepted for publication in A
Jet Acceleration by Tangled Magnetic Fields
We explore the possibility that extragalactic radio jets might be accelerated
by highly disorganized magnetic fields that are strong enough to dominate the
dynamics until the terminal Lorentz factor is reached. Following the
twin-exhaust model by Blandford & Rees (1974), the collimation under this
scenario is provided by the stratified thermal pressure from an external
medium. The acceleration efficiency then depends on the pressure gradient of
that medium. In order for this mechanism to work there must be continuous
tangling of the magnetic field, changing the magnetic equation of state away
from pure flux freezing (otherwise conversion of Poynting flux to kinetic
energy flux is suppressed). This is a complementary approach to models in which
the plasma is accelerated by large scale ordered fields. We include a simple
prescription for magnetic dissipation, which leads to tradeoffs among
conversion of magnetic energy into bulk kinetic energy, random particle energy,
and radiation. We present analytic dynamical solutions of such jets, assess the
effects of radiation drag, and comment on observational issues, such as the
predicted polarization and synchrotron brightness. Finally, we try to make the
connection to observed radio galaxies and gamma-ray bursts.Comment: 15 pages, 10 figures, accepted for publication in Ap
- âŠ