87 research outputs found
Millimetre-VLBI Monitoring of AGN with Sub-milliarcsecond Resolution
Global millimetre VLBI allows detailed studies of the most central jet
regions of AGN with unprecedent spatial resolution of a few 100-1000
Schwartzschild radii to be made. Study of these regions will help to answer the
question how the highly relativistic AGN jets are launched and collimated.
Since the early 1990s, bright mm-sources have been observed with global 3 mm
VLBI. Here we present new images from an ongoing systematic analysis of the
available observations. In particular, we focus on the structure and structural
evolution of the best observed AGN jets, taking 3C 454.3 as a characteristic
example. This core-dominated and highly variable quasar shows a complex
morphology with individual jet components accelerating superluminally towards
the outer structure. We briefly discuss the X-ray properties of 3C 454.3 and
present its radio- to X-ray large-scale brightness distribution.Comment: 4 pages, 4 figures, Proceedings of the 7th EVN Symposium held in
Toledo, Spain in October 2004, needs evn2004.cl
Imported lassa fever in Germany: molecular characterization of a new lassa virus strain.
We describe the isolation and characterization of a new Lassa virus strain imported into Germany by a traveler who had visited Ghana, Côte D'Ivoire, and Burkina Faso. This strain, designated "AV," originated from a region in West Africa where Lassa fever has not been reported. Viral S RNA isolated from the patient's serum was amplified and sequenced. A long-range reverse transcription polymerase chain reaction allowed amplification of the full-length (3.4 kb) S RNA. The coding sequences of strain AV differed from those of all known Lassa prototype strains (Josiah, Nigeria, and LP) by approximately 20%, mainly at third codon positions. Phylogenetically, strain AV appears to be most closely related to strain Josiah from Sierra Leone. Lassa viruses comprise a group of genetically highly diverse strains, which has implications for vaccine development. The new method for full-length S RNA amplification may facilitate identification and molecular analysis of new arenaviruses or arenavirus strains
A High-Frequency and Multi-Epoch VLBI Study of 3C 273
We show results from a 7 year VLBI monitoring programme of 3C273 at
millimeter wavelengths. We find evidence for component acceleration, motion or
rotation of fluid dynamical patterns in the VLBI jet, and evidence for an
outburst-ejection relation between Gamma-ray flares and the appearance of new
jet components.Comment: 4 pages, 5 figures, to appear in: Particles and Fields in Radio
Galaxies, a conference held at Oxford August 3-5, 2000, ASP Conference
Series, eds. R.A. Laing and K.M. Blundell, in pres
Nonlinear Radiation Pressure and Stochasticity in Ultraintense Laser Fields
The radiation force on a single electron in an ultraintense plane wave () is calculated and shown to be proportional to in the
high- limit for arbitrary waveform and polarization. The cyclotron motion of
an electron in a constant magnetic field and an ultraintense plane wave is
numerically found to be quasiperiodic even in the high- limit if the
magnetic field is not too strong, as suggested by previous analytical work. A
strong magnetic field causes highly chaotic electron motion and the boundary of
the highly chaotic region of parameter space is determined numerically.
Applications to experiments and astrophysics are briefly discussed.Comment: 5 pages, 4 figures; uses RevTex, epsf macros. Corrected, expanded
versio
50 µas resolution VLBI images of AGN's at λ3mm
We present 15 images from the global mm-VLBI sessions in 1990 April at 100GHz and 1993 April at 86GHz. These observations probe the central engines of the 16 observed AGN's with up to 50 µas resolution. Among other sources previously observed with λ3mm VLBI we present the first λ3mm maps of 0735+178, 0748+126, 1055+018, 2145+067, and CTA102, in total we have been able to image 13 out of the 16 observed sources. 6 out of the 13 imaged sources observed exhibit curvature and rapid structural changes, although the low dynamic range in two thirds of the maps limits the detection of weak features. Most of the sources have unresolved cores even at this high resolution. There is substantial evidence that the observed sources can be grouped into two general groups: A misaligned population with parsec scale jets in the form of low pitch helices and an aligned population with straight jets with small changes in PA due to intrinsic bends
Towards the Event Horizon - High Resolution VLBI Imaging of Nuclei of Active Galaxies
We report on new developments in VLBI, with emphasis on experiments performed
at the highest frequencies possible to date (so called mm-VLBI). We have
observed the nucleus of M 87 (Virgo A) with global VLBI at 3 mm. We show a new
image of the inner-most jet region with an angular resolution of approx. 300 x
60 micro-arcseconds. In terms of Schwarzschild radii, this leads to an upper
limit of the jet base of approx. 100 x 20 Schwarzschild radii. We also report
on two VLBI pilot-experiments, which demonstrate the technical feasibility of
global VLBI at 150 and 230 GHz (2 mm and 1.3 mm). The experiments lead to upper
limits to the size of the unresolved AGN-cores in the 25 - 30 micro-arcsecond
range. The participation of new and near-future mm-telescopes (like APEX,
CARMA, SMA, LMT, ALMA, etc.) in global mm-VLBI will provide the necessary
sensitivity for the imaging of black holes and their immediate environment.Comment: To appear in the conference proceedings "Exploring the Cosmic
Frontier: Astrophysical Instruments for the 21st Century", held in Berlin,
Germany, May 17 - 21, 2004, ESO Astrophysical Symposia Series, in press.
Paper contains 2 pages, 1 figur
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