Structure of a distant quasar uncovered

First high-resolution image with the radio telescope LOFAR succeeded

Radio pictures of the quasar 3C 196 at 4 - 10 m wavelength (frequency: 30 - 80 MHz). Left: Data exclusively from the Dutch LOFAR stations. The resolution is not sufficient for the identification of substructures. Right: Enlarged section of the central image area, including the German LOFAR stations. The resolution of the image is about 10 times higher and shows for the first time a number of details in this wavelength range. The colors correspond to what the human eye could see if it were sensitive to wavelengths that are 10 million times greater than those of visible light. © Olaf Wucknitz / University of Bonn
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With the LOFAR (LOw Frequency Arrays) radio telescope, an international team of scientists has succeeded in obtaining the first high-resolution image of a distant quasar for radio waves in the meter range. This wavelength range was previously not accessible for such detailed measurements, since this radio telescopes must be networked together in large mutual distance.

The new recording of the detailed structure of the quasar 3C 196 between four and ten meter wavelength could already be realized with a small part of the stations of the complete LOFAR network. Later it will span a vast area of ​​Europe.

First test measurements

The Max Planck Institute for Radio Astronomy (Bonn) and the Max Planck Institute for Astrophysics (Garching) both operate a station of the European LOFAR Telescope, which is coordinated by the Dutch Institute of Radio Astronomy, ASTRON. After test measurements with individual LOFAR antennas, eight stations of the LOFAR could now be interconnected for a common measurement for the first time. For this purpose, five LOFAR stations in the Netherlands were networked with three stations in Germany, namely Effelsberg near Bonn, Tautenburg near Jena and Unterweilbach near Munich. All antennas were aligned to the Quasar 3C 196, a powerful radio source several billion light years away.

"We selected this object for our first test measurements because we know its structure from high-resolution observations at shorter wavelengths quite well, " says Olaf Wucknitz from the Argelander Institute for Astronomy (AIfA) at the University of Bonn. "The goal was initially not to find something new, but to identify the same or at least similar structures even at very long wavelengths to confirm that the new instrument works excellently. Without the German stations we only see a blurred spot without any substructures. But as soon as we add the long baselines, all the details open up. "

Researchers are breaking new ground

Radio observations of the sky in the wavelength range covered by LOFAR are not entirely new. In fact, the pioneers of radio astronomy started in this area in the 1930s. However, they were only able to create fairly coarse sky maps and to determine positions and radiation intensities of individual objects. display

"We are now returning to a long neglected wavelength range, " says Michael Garrett of ASTRON. But now we are able to detect much weaker objects and, more importantly, resolve fine details. This opens up a whole range of new opportunities for research. And Wucknitz adds: LOThe high resolution and high sensitivity of LOFAR mean that we really break new ground; the analysis of the data was also correspondingly time-consuming. We had to develop a whole new set of analysis techniques. Nevertheless, the creation of the pictures is remarkably well done. The quality of the data is amazing

Gravity lenses in the sights

The next step for Wucknitz will be to use LOFAR for the investigation of so-called gravitational lenses, in which the light of distant objects is distorted by large mass accumulations. High resolution is required to distinguish individual structures. That would not be possible without the international LOFAR stations.

The angular resolution of a network of radio telescopes, that is the extension of the smallest structures that can be resolved and distinguished, depends directly on the distance between each telescope. The larger the baselines are with respect to the observed wavelength of the radiation, the better the resolution achieved. At present, the German LOFAR stations are contributing the first major baselines to the entire network and are increasing the resolution by a factor of 10 over the use of only the Dutch stations.

Signals from the early days of the universe on the track

"We want to use LOFAR to search for signals from the early days of the Universe, " says Benedetta Ciardi from the Max Planck Institute for Astrophysics (MPA) in Garching. Because I come from theoretical astrophysics myself, I never thought that I could ever find a radio picture so exciting. But the new results are already fascinating

Further improvement should soon be achieved by observations at shorter wavelengths, which can increase the resolution by a factor of 4, the researchers say. In addition, the quality of the images will improve significantly by adding more LOFAR stations. The picture of the quasar 3C 196 is only a first, albeit important, step.

On the way to the finished network

"The image quality of the finished network will depend very much on the uniformity with which large areas of Europe can be covered with individual LOFAR stations" Anton, says Anton Zensus from the Max Planck Institute for Radio Astronomy (MPIfR). The German stations already make an invaluable contribution to the international network. But what we could still do well would be a station in northern Germany, with which we will close the gap between our current stations and those of our Dutch friends. That would significantly improve the picture quality again

(Argelander Institute for Astronomy, University of Bonn / Max Planck Institute for Radio Astronomy, 02.06.2010 - DLO)