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After first tests of the individual antennas, the observations now bring
together eight stations of the "LOw Frequency ARray" (LOFAR), Five
stations in the Netherlands were connected with three stations in
Germany: Effelsberg near Bonn, Tautenburg near Jena and Unterweilenbach
near Munich. All antennas were targeted at the quasar 3C 196, a strong
radio source at a distance of several billions of light years. "We chose
this object for the first tests, because we know its structure very well
from observations at shorter wavelengths", explains Olaf Wucknitz
(AIfA). "The goal was not to find something new but to see the same or
similar structures also at very long wavelengths to confirm that the new
instrument really works. Without the German stations, we only saw a
fuzzy blob, no sub-structure. Once we included the long baselines, all
the details showed up."
Observations at wavelengths covered by LOFAR are not new. In fact, the
pioneers of radio astronomy started their work in the same range.
However, they were only able to produce very rough maps of the sky and
to measure just the positions and intensities of objects. "We are now
returning to this long neglected wavelength range", says Michael
Garrett, general director of ASTRON (The Netherlands), the research
institute in charge of the international LOFAR project. "But this time
we are able to see much fainter objects and, even more important, to
image very fine details. This offers entirely new opportunities for
astrophysical research."
"The high resolution and sensitivity of LOFAR mean that we are really
entering uncharted territory, and the analysis of the data was
correspondingly intricate", adds Olaf Wucknitz. "We had to develop
completely new techniques. Nevertheless, producing the images went
surprisingly smoothly in the end. The quality of the data is stunning."
The next step for Wucknitz is to use LOFAR to study so-called
gravitational lenses, where the light from distant objects is distorted
by large mass concentrations. High resolution is required to see the
interesting structures of these objects. This research would be
impossible without the international stations.
The resolution of an array of radio telescopes, i.e. the size of the
smallest structures that it can resolve and distinguish, depends
directly on the separation between the telescopes. The larger these
baselines are relative to the observed wavelength, the better the
achieved resolution. Currently the German stations provide the first
long baselines of the array and improve the resolution by a factor of
ten over just using the Dutch stations.
"We want to use LOFAR to search for signals from very early epochs of
the Universe", says Benedetta Ciardi from the Max Planck Institute for
Astrophysics (MPA) in Garching. "Having a completely theoretical
background myself, I never had thought that I would get excited over a
radio image, but this result is really fascinating."
Further improvement should come very soon with observations at slightly
shorter wavelengths, which will increase the resolution by another
factor of four. In addition, the imaging quality will improve
significantly with more stations coming online soon. The image of quasar
3C 196 therefore is just the first but very important step.
"The image quality of the final array depends crucially on the
uniformity with which large areas are covered with stations", says Anton
Zensus, director at the Max Planck Institute for Radioastronomy (MPIfR)
and in charge of the VLBI research group at the institute. "The German
stations are already an indispensable contribution to the international
array. What we are still lacking, however, is a station in northern
Germany to close the gap between our stations and the ones of our Dutch
friends. This would increase the image quality a lot."
Notes
The International LOFAR telescope (ILT) is being primarily built by
ASTRON, the Netherlands Institute for Radio Astronomy, in collaboration
with a number of international partners. The LOFAR station at Effelsberg
is operated by MPIfR, the one in Unterweilenbach by MPA and the
Tautenburg station by Thüringer Landessternwarte. The German LOFAR
partners form GLOW, the German LOng Wavelength consortium.
In its final stages, the international LOFAR array will consist of at
least 36 stations in the Netherlands and eight stations in Germany,
France, the United Kingdom and Sweden. Currently 22 stations are
operational and more are being set up in Bornim near Potsdam (Germany),
Chilbolton (UK), Onsala (Sweden) and Nançay (France). Each station
consists of hundreds of dipole antennas that are connected
electronically to form a huge radio telescope that will cover half of
Europe. With the novel techniques introduced by LOFAR, it is no longer
necessary to point the radio antennas at specific objects of interest.
Instead it will be possible to observe several regions of the sky
simultaneously.
The data from all LOFAR stations are transferred via powerful fibre
optic cables in research networks to the computing centre in Groningen
in the north of the Netherlands. There they are combined and pre-
processed for the final analysis which can be performed either there or
at any of the participating institutes, in this case at the Argelander-
Institute for Astronomy in Bonn.
Further Information:
 Argelander-Institut für Astronomie (AIfA), Bonn.
Max-Planck-Institut für Radioastronomie. (MPIfR).
German LOng Wavelength (GLOW).
Netherlands Institute for Radio Astronomy (ASTRON).
LOw Frequency ARray (LOFAR), International Web site.
LOFAR at MPA
Contact:
Hannelore Hämmerle
Press Officer
Max Planck Institute for Astrophysics
and Max Planck Institute for extraterrestrial Physics
Phone: +49 89 30000-3980
E-Mail: hhaemmerle mpa-garching.mpg.de
Benedetta Ciardi
Max Planck Institute for Astrophysics
Phone: +49 89 30000-2018
E-mail: bciardimpa-garching.mpg.de
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