333 research outputs found
3C 216: A Powerful FRII Seyfert 1 Galaxy
3C 216 has a weak accretion flow luminosity, well below the Seyfert1/QSO
dividing line, weak broad emission lines (BELs) and powerful radio lobes. As a
consequence of the extreme properties of 3C 216, it is the most convincing
example known of an FR II radio source that is kinetically dominated: the jet
kinetic luminosity, , is larger than the total thermal luminosity (IR to
X-ray) of the accretion flow, . Using three independent estimators for
the central black hole mass, we find that the jet in 3C 216 is very
super-Eddington, , where is the long
term time averaged , calculated at 151 MHz. It is argued that 3C 216
satisfies the contemporaneous kinetically dominated condition, , either presently or in the past based on the rarity of
quasars. The existence of AGN is a strong constraint
on the theory of the central engine of FRII radio sources
The inner radio jet region and the complex environment of SS433
We present multi-frequency VLBA+VLA observations of SS433 at 1.6, 5 and 15
GHz. These observations provide the highest angular resolution radio spectral
index maps ever made for this object. Motion of the components of SS433 during
the observation is detected. In addition to the usual VLBI jet structure, we
detect two radio components in the system at an anomalous position angle. These
newly discovered radio emitting regions might be related to a wind-like
equatorial outflow or to an extension of the accretion disk. We show that the
radio core component is bifurcated with a clear gap between the eastern and
western wings of emission. Modelfitting of the precessing jets and the moving
knots of SS433 shows that the kinematic centre -- i.e. the binary -- is in the
gap between the western and eastern radio core components. Spectral properties
and observed core position shifts suggest that we see a combined effect of
synchrotron self-absorption and external free-free absorption in the innermost
AU-scale region of the source. The spatial distribution of the ionized matter
is probably not spherically symmetric around the binary, but could be
disk-like.Comment: Accepted for publication by Astronomy and Astrophysic
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
A Generalization of the Convex Kakeya Problem
Given a set of line segments in the plane, not necessarily finite, what is a
convex region of smallest area that contains a translate of each input segment?
This question can be seen as a generalization of Kakeya's problem of finding a
convex region of smallest area such that a needle can be rotated through 360
degrees within this region. We show that there is always an optimal region that
is a triangle, and we give an optimal \Theta(n log n)-time algorithm to compute
such a triangle for a given set of n segments. We also show that, if the goal
is to minimize the perimeter of the region instead of its area, then placing
the segments with their midpoint at the origin and taking their convex hull
results in an optimal solution. Finally, we show that for any compact convex
figure G, the smallest enclosing disk of G is a smallest-perimeter region
containing a translate of every rotated copy of G.Comment: 14 pages, 9 figure
Images of an equatorial outflow in SS433
We have imaged the X-ray binary SS433 with unprecedented Fourier-plane
coverage at 6cm using simultaneously the VLBA, MERLIN, and the VLA, and also at
20cm with the VLBA. At both wavelengths we have securely detected smooth,
low-surface brightness emission having the appearance of a `ruff' or collar
attached perpendicularly to the well-studied knotty jets in this system,
extending over at least a few hundred AU. We interpret this smooth emission as
a wind-like outflow from the binary, and discuss its implications for the
present evolutionary stage of this system.Comment: Accepted by ApJ Letter
Vibrational signature of broken chemical order in a GeS2 glass: a molecular dynamics simulation
Using density functional molecular dynamics simulations, we analyze the
broken chemical order in a GeS glass and its impact on the dynamical
properties of the glass through the in-depth study of the vibrational
eigenvectors. We find homopolar bonds and the frequencies of the corresponding
modes are in agreement with experimental data. Localized S-S modes and 3-fold
coordinated sulfur atoms are found to be at the origin of specific Raman peaks
whose origin was not previously clear. Through the ring size statistics we
find, during the glass formation, a conversion of 3-membered rings into larger
units but also into 2-membered rings whose vibrational signature is in
agreement with experiments.Comment: 11 pages, 8 figures; to appear in Phys. Rev.
- …