1,114 research outputs found
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.
A Global 86GHz VLBI Survey of Compact Radio Sources
We present results from a large 86GHz global VLBI survey of compact radio
sources. The main goal of the survey is to increase by factors of 3--5 the
total number of objects accessible for future 3-mm VLBI imaging. The survey
observations reach the baseline sensitivity of 0.1Jy and image sensitivity of
better than 10 mJy/beam. The total of 127 compact radio sources have been
observed. The observations have yielded images for 109 sources, extending the
database of the sources imaged at 86GHz with VLBI observation by a factor of 5,
and only 6 sources have not been detected. The remaining 12 objects have been
detected but could not be imaged due to insufficient closure phase information.
Radio galaxies are less compact than quasars and BL Lacs on sub-milliarcsecond
scale. Flux densities and sizes of core and jet components of all imaged
sources have been estimated using Gaussian model fitting. From these
measurements, brightness temperatures have been calculated, taking into account
resolution limits of the data. The cores of 70% of the imaged sources are
resolved. The core brightness temperatures of the sources peak at K and only 1% have brightness temperatures higher than K.
Cores of Intraday Variable (IDV) sources are smaller in angular size than
non-IDV sources, and so yield higher brightness temperatures.Comment: 72 pages, 12 figures, accepted for publication in the Astronomical
Journa
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
- …