First high quality wide field LOFAR image

Astronomers and engineers have together produced the first high quality image with a LOFAR station. The data were collected with 96 low band antennas located in four fields at the heart of the array in the province of Drenthe in the North-East of the Netherlands, and transported over a dedicated glass-fibre link to a central processing facility at the University of Groningen, some 60 km away. The quality of the results confirm LOFAR’s undoubted scientific potential and were an important demonstration of the design that was presented at the Critical Design Review held in Assen on 17 & 18 April. A panel of experts reviewed the status of the project and gave the green light for the construction phase, which will start in the second half of this year. Large, international participation in a LOFAR scientific workshop in Emmen (Drenthe) this week, shows that there is an active and growing community of users eager to make use of a telescope that will open up a new window on the Universe.  

LOFAR (Low Frequency Array) will be the largest radio telescope ever built, currently under construction by a consortium led by ASTRON, the Netherlands Foundation for Research in Astronomy. When finished, LOFAR will consist of 15,000 small antennas, distributed over 77 stations in the North East of the Netherlands and nearby parts of Germany. The array will operate at the lowest frequencies that can be observed from Earth, between 10 and 240 MHz. Plans exist for the extension of the array beyond its initial 100 km scale, by building stations further into Germany and also the UK, France, Sweden, Poland and Italy. The first “foreign” station is under construction in Effelsberg near Bonn in Germany and recently held its “first light” ceremony. LOFAR is an innovative sensor network which, in addition to the antennas used for radio astronomy, also consists of geophysical and precision-agriculture sensors.  

The image (Figure 1) was made using 29 hours of data taken on February 23/24 2007 and demonstrates the capability of the current system. “What makes this image impressive is the formidable dynamic range it already shows, we can’t wait to get our hands on data from more LOFAR stations” says Ger de Bruyn, astronomer from ASTRON and the University of Groningen. The 96 low band antennas are optimized for operation in the 30-80 MHz frequency range, below the commercial FM-radio band. These antennas are distributed over four fields, which are up to 400 metres apart (see Figure 2). A second type of antenna, capable of operating at higher frequencies (120-240 MHz) will follow in the next few months. Initial processing takes place on location with dedicated digital hardware. Afterwards, the signals are transported to the central processing facility at the University of Groningen where they are combined. A large part of the current success lies in the processing which has been applied to the data and made possible by new software developed by a dedicated team of programmers and developers.   

The LOFAR project held its Critical Design Review last week in Assen, The Netherlands. A panel of seven experts in antenna design, digital processing, high performance computing, system integration and radio astronomy scrutinized the design, visited the site where the core of the array will be built and were shown the first results. The panel judged that it could not see any major show stoppers that should prevent construction of the telescope, although it noted that significant challenges remained. These lie mainly in the fields of calibration and software development – areas that can only be tackled once more observations have been made.   

This week, 120 astronomers from 15 nations assemble in Emmen, located some 20 km from the core of the array, for a workshop to discuss a wide range of scientific projects that can be carried out with LOFAR. One of the topics is the detection of signals from neutral hydrogen from the Epoch of Reionization, when the first galaxies ionized the Universe and ended the Dark Ages. Also on the programme are studies of distant radio galaxies, variable and transient radio sources and radio emission caused by cosmic ray particles and our Sun.  It shows that there is an active and growing community of users eager to make use of a telescope that will open up a new window on the Universe.  

LOFAR is funded by the Netherlands government in the BSIK programme for interdisciplinary research for improvements of the knowledge infrastructure. Additional funding is being provided by the European Community, European Regional Development Fund and the “Northern Netherlands Assembly (SNN)” EZ/KOMPAS. 

ASTRON is an institute of the Netherlands Organization for Scientific Research, NWO.

Note on images: 

Websites: www.lofar.org and www.astron.nl to download high resolution versions of the figures mentioned in the press release. 

Contacts: 

LOFAR:  Michiel van Haarlem, LOFAR Managing Director, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo – Phone: +31 (0)521 596 562  e-mail: haarlem@astron.nl 

ASTRON:   Marjan Tibbe, PR & Communication, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo – Phone: +31 (0)521 595 162   e-mail: tibbe@astron.nl