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Analysing first imaging data from LOFAR
LOFAR, the Low Frequency Array, is a next-generation radio telescope that is being built in the Netherlands and neighboring countries. It will carry out a broad range of fundamental astrophysical studies. An important goal of LOFAR is to explore the low-frequency radio sky by means of a series of unique surveys. The main aim of these surveys is to advance our understanding of the formation of galaxies, clusters and active galactic nuclei. These surveys will be carried out and scientifically exploited by a large international science team, consisting of 75 staff astronomers, 17 postdocs and 15 PhD students. Currently LOFAR is in its role-out phase. At the end of November, 12 stations were operational, and with the current projected rate of building, the complete LOFAR facility with 36 Dutch stations should be ready at the end of 2010. Also the main software pipeline that is capable of delivering maps of the radio sky from the basic data is advancing rapidly. The main challenge for the survey project is to ensure that high dynamic range thermal noise limited images with a stable point-spread function can be made over the entire accessible sky and over LOFAR's full frequency range. The serious issues that need to be tackled before deep and scientifically useful maps can be made include
(i) an efficient usage of the computational resources,
(ii) an effective removal of radio frequency interference (RFI),
(iii) dealing with the corrupting influence of the ionosphere, and,
(iv) properly correcting for the station beams.
To deal with all these issues, the survey team has been and is organizing a series of `busy weeks’. The idea is that a team of astronomers from the survey team attempts to tackle a number of issues related to the challenges just mentioned. Three busy weeks have already been held (Aug 17-21, Sept 28-Oct 2, Oct 19-23). During these busy weeks very basic functionalities of the system were tested. The fifth busy week has been held at the Lorentz center (Jan 25-29).
With 28 participants, recent LOFAR data was carefully scrutinized. Various existing (aips, casa, myriad) and new (BBS) radio reduction packages were used to reduce the new LOFAR data. As there was a constant interaction between software developers sand astronomers significant progress could be made. A high light was the production of a deep image of3C61.1 (See figure 1).
Fig. 1. High and low frequency images of 3C61.1.
For comparison, images of 3C61.1 from other radio telescopes are shown in Figure 1.
The Lorentz center was ideal for this meeting. The many offices with computers allowed the participants to work very hard on the data. One or twice a day plenary sessions were held during which progress was reported and ideas where exchanged on next steps to take. During the conclusion, a list of issues was drafted to be used by the (software) developers to steer their work.