4,640 research outputs found
Parsec Scale Properties of Markarian 501
We present the results of a high angular resolution study of the BL Lac
object Markarian 501 in the radio band. We consider data taken at 14 different
epochs, ranging between 1.6 GHz and 22 GHz in frequency, and including new
Space VLBI observations obtained on 2001 March 5 and 6 at 1.6 and 5 GHz. We
study the kinematics of the parsec-scale jet and estimate its bulk velocity and
orientation with respect to the line of sight. Limb brightened structure in the
jet is clearly visible in our data and we discuss its possible origin in terms
of velocity gradients in the jet. Quasi-simultaneous multi-wavelength
observations allow us to map the spectral index distribution and to compare it
to the jet morphology. Finally, we estimate the physical parameters of the
parsec-scale jet.Comment: accepted for publication in ApJ; 24 pages with 17 figures (fig. 1 and
fig. 2 available only as .jpg files
The Effect of Propofol on the Canine Sphincter of Oddi
To assess the effect of propofol on the canine sphincter of Oddi (SO), sphincter of Oddi manometry (SOM)
was performed in fasting dogs which had undergone cholecystectomy and placement of modified Thomas
duodenal cannulae. Using two water-perfused, single-lumen manometric catheters, SO and duodenal
pressures were measured simultaneously. Baseline SO activity was recorded for at least one complete
interdigestive cycle followed by bolus injections of propofol (Diprivan ®) (N = 31) from 0.1 to 4.0 mg/kg
during Phase I of the Migrating Motor Complex (MMC)
Shear-free, Irrotational, Geodesic, Anisotropic Fluid Cosmologies
General relativistic anisotropic fluid models whose fluid flow lines form a
shear-free, irrotational, geodesic timelike congruence are examined. These
models are of Petrov type D, and are assumed to have zero heat flux and an
anisotropic stress tensor that possesses two distinct non-zero eigenvalues.
Some general results concerning the form of the metric and the stress-tensor
for these models are established. Furthermore, if the energy density and the
isotropic pressure, as measured by a comoving observer, satisfy an equation of
state of the form , with , then
these spacetimes admit a foliation by spacelike hypersurfaces of constant Ricci
scalar. In addition, models for which both the energy density and the
anisotropic pressures only depend on time are investigated; both spatially
homogeneous and spatially inhomogeneous models are found. A classification of
these models is undertaken. Also, a particular class of anisotropic fluid
models which are simple generalizations of the homogeneous isotropic
cosmological models is studied.Comment: 13 pages LaTe
The Covariant Approach to LRS Perfect Fluid Spacetime Geometries
The dynamics of perfect fluid spacetime geometries which exhibit {\em Local
Rotational Symmetry} (LRS) are reformulated in the language of a
"threading" decomposition of the spacetime manifold, where covariant fluid and
curvature variables are used. This approach presents a neat alternative to the
orthonormal frame formalism. The dynamical equations reduce to a set of
differential relations between purely scalar quantities. The consistency
conditions are worked out in a transparent way. We discuss their various
subcases in detail and focus in particular on models with higher symmetries
within the class of expanding spatially inhomogeneous LRS models, via a
consideration of functional dependencies between the dynamical variables.Comment: 25 pages, uuencoded/compressed postscript fil
Multiwavelength Observations of the Second Largest Known FR II Radio Galaxy, NVSS 2146+82
We present multi-frequency VLA, multicolor CCD imaging, optical spectroscopy,
and ROSAT HRI observations of the giant FR II radio galaxy NVSS 2146+82. This
galaxy, which was discovered by the NRAO VLA Sky Survey (NVSS), has an angular
extent of nearly 20' from lobe to lobe. The radio structure is normal for an FR
II source except for its large size and regions in the lobes with unusually
flat radio spectra. Our spectroscopy indicates that the optical counterpart of
the radio core is at a redshift of z=0.145, so the linear size of the radio
structure is ~4 h_50^-1 Mpc. This object is therefore the second largest FR II
known (3C 236 is ~6 h_50^-1 Mpc). Optical imaging of the field surrounding the
host galaxy reveals an excess number of candidate galaxy cluster members above
the number typically found in the field surrounding a giant radio galaxy. WIYN
HYDRA spectra of a sample of the candidate cluster members reveal that six
share the same redshift as NVSS 2146+82, indicating the presence of at least a
``rich group'' containing the FR II host galaxy. ROSAT HRI observations of NVSS
2146+82 place upper limits on the X-ray flux of 1.33 x 10^-13 ergs cm^-2 s^-1
for any hot IGM and 3.52 x 10^-14 ergs cm^-2 s^-1 for an X-ray AGN, thereby
limiting any X-ray emission at the distance of the radio galaxy to that typical
of a poor group or weak AGN. Several other giant radio galaxies have been found
in regions with overdensities of nearby galaxies, and a separate study has
shown that groups containing FR IIs are underluminous in X-rays compared to
groups without radio sources. We speculate that the presence of the host galaxy
in an optically rich group of galaxies that is underluminous in X-rays may be
related to the giant radio galaxy phenomenon.Comment: 46 pages, 15 figures, AASTeX aaspp4 style, accepted for publication
in A
The galactic magnetic field in the quasar 3C216
Multifrequency polarimetric observations made with the Very Long Baseline
Array of the quasar 3C216 reveal the presence of Faraday rotation measures
(RMs) in excess of 2000 rad/m**2 in the source rest frame, in the arc of
emission located at ~ 140 mas from the core. Rotation measures in the range
-300 - +300 rad/m**2 are detected in the inner 5 mas (~30 parsecs). while the
rotation measures near the core can be explained as due to a magnetic field in
the narrow line region, we favor the interpretation for the high RM in the arc
as due to a ``local'' Faraday screen, produced in a shock where the jet is
deflected by the interstellar medium of the host galaxy. Our results indicate
that a galacit magnetic field of the order of 50 microGauss on a scale greater
than 100 pc must be present in the galactic medium.Comment: 23 pages, 3 tables, 11 figures. To appear on The Astronomical
Journal, November 1999 Issu
General Relativistic 1+3 Orthonormal Frame Approach Revisited
The equations of the 1+3 orthonormal frame approach are explicitly presented
and discussed. Natural choices of local coordinates are mentioned. A
dimensionless formulation is subsequently given. It is demonstrated how one can
obtain a number of interesting problems by specializing the general equations.
In particular, equation systems for ``silent'' dust cosmological models also
containing magnetic Maxwell fields, locally rotationally symmetric spacetime
geometries and spatially homogeneous cosmological models are presented. We show
that while the 3-Cotton--York tensor is zero for Szekeres dust models, it is
nonzero for a generic representative within the ``silent'' class.Comment: 41 pages, uufiles encoded postscript file, submitted to Phys. Rev.
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