767 research outputs found
Dual frequency VSOP imaging of the jet in S5 0836+710
The luminous high-redshift (z=2.17) quasar S50836+710 has been observed in
October 1997 with the VSOP at 1.6 GHz and 5 GHz. We report here a previously
unpublished image made from the data at 1.6 GHz and compare the structure of a
relativistic jet in this quasazr at the two frequencies. We present a spectral
index image tracing spectral properties of the jet up to ~40 milliarcsecond
distance from the nucleus. The curved jet ridge line observed in the images and
the spectral index distribution can be described by Kelvin-Helmholtz
instability developing in a relativistic outflow with a Mach number of ~6. In
this description, the overall ridge line of the jet is formed by the helical
surface mode of Kelvin-Helmholtz instability, while areas of flatter spectral
index embedded into the flow correspond to pressure enhancements produced by
the elliptical surface mode of the instability. An alternative explanation
involving a sequence of slowly dissipating shocks cannot be ruled out at this
point.Comment: 7 pages, 4 figures, pasj00.cls. Submitted to PASJ. (Corrected figure
orientation
High-frequency VLBI observations of SgrA* during a multi-frequency campaign in May 2007
In May 2007 the compact radio source Sgr A* was observed in a global
multi-frequency monitoring campaign, from radio to X-ray bands. Here we present
and discuss first and preliminary results from polarization sensitive VLBA
observations, which took place during May 14-25, 2007. Here, Sgr A* was
observed in dual polarization on 10 consecutive days at 22, 43, and 86 GHz. We
describe the VLBI experiments, our data analysis, monitoring program and show
preliminary images obtained at the various frequencies. We discuss the data
with special regard also to the short term variability.Comment: 6 pages, 5 figures;necessary style files included; contribution for
the conference "The Universe under the Microscope" (AHAR 2008), held in Bad
Honnef (Germany) in April 2008, to be published in Journal of Physics:
Conference Series by Institute of Physics Publishing, R. Schoedel, A. Eckart,
S. Pfalzner, and E. Ros (eds.
The Role of Millimeter VLBI Observations in AGN Research
VLBI at millimeter wavelengths (mm-VLBI) allows the detailed imaging of
compact galactic and extragalactic radio sources with micro-arcsecond scale
resolution, unaccessible by other observing techniques. Here we discuss the
scientific potential of mm-VLBI for present and future research on `Active
Galactic Nuclei' (AGN) and their powerful relativistic jets. With the new
generation of large radio telescopes and interferometer arrays operating in the
millimeter radio bands (e.g. ALMA), the ultimate vicinity of super massive
Black Holes, and eventually even their event horizon, could be imaged. With its
large collecting area, and in combination with these future telescopes, the
Sardinia Radio Telescope could form the World's `sharpest' astronomical imaging
machine.Comment: 10 pages, 1 table, 7 figures. An inveited talk held at the Sardinia
Radiotelescope Conference in Cagliari, Sardinia, on November 7-10, 200
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