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Initiator: ASTRON Netherlands Institute for Radio Astronomy

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This project was co-financed by the EU, the European Fund for Regional Development and the Northern Netherlands Provinces (SNN), and EZ/KOMPAS.

First pulsar detection with LOFAR station

Astronomers from ASTRON and the University of Amsterdam successfully detected the pulsar PSR B0329+54 using the first LOFAR station, CS-01. The measurement took 15 minutes and used six of the prototype High Band Antennas (HBAs) that were recently installed at the "Core Station 1" field in Exloo, Drenthe, The Netherlands. The High Band Antennas operate at frequencies between 115-240 MHz. The search for the pulsar used 48 frequency bands in the range 170-230 MHz. The pulsar was observed in 44 of these 48 bands, indicating that the radio spectrum at the site is relatively clean, in line with earlier experiments with the Westerbork Synthesis Radio Telescope (WSRT). The results show that the technical performance of the High Band Antennas is excellent. With this experiment, all LOFAR subsystems have now been successfully verified in astronomical observations.

Pulsars are rotating neutron stars with a diameter of only ~ 20 kilometer. They are the remnants of massive stars that have collapsed after they have used up all their nuclear fuel. These objects have extremely strong magnetic fields and emit radio-waves from their magnetic poles, just like the beam of a lighthouse. Ed van den Heuvel, astronomy professor at the University of Amsterdam, remarks: "It’s fantastic to see that with only six antennas, which together are five hundred times less sensitive than the final LOFAR telescope, we can now already detect these pulsars! Last year, 40 years after the discovery of pulsars, observations with the Westerbork telescope finally gave some insights in the mechanism radio-pulsars use to generate their radio waves. It turned out that this mechanism will show itself most clearly at the low radio-frequencies that will be observed by LOFAR. Simulations predict that the full LOFAR will discover some thousand new pulsars, doubling the number of pulsars in the Northern hemisphere, and in addition, allowing us to study them in much more detail."

This spring, LOFAR successfully passed an important milestone: the Critical Design Review of the technical project. On April 17-18, the design was presented to an independent review board. The advice of the board was to start vigorously with the construction of the first 20 LOFAR stations. Ultimately the ambition is to build 77 LOFAR stations, but funding still has to be secured for the final phase of 20 to 30 stations. The science team is also considering the option of deploying smaller stations at all targeted locations. In addition, there are now serious plans for the construction of 10 to 15 LOFAR stations elsewhere in Europe: six to nine in Germany, three in the UK, one in France and possibly also in Sweden, Poland, Ukraine and Italy. The first of these European LOFAR stations has been constructed already next to the 100-metre Effelsberg radio telescope near Bonn, Germany. The European LOFAR stations are an important extension for LOFAR. Combining stations at these large distances with those in the Netherlands will increase the spatial resolution of LOFAR images by a factor of 10. This is especially important for detailed studies of galaxies.

Meanwhile, ASTRON’s Radio Observatory is beginning to gear-up for the operational phase of LOFAR as an astronomical facility. Since 1970, the Radio Observatory has been responsible for the operations of the Westerbork Synthesis Radio Telescope (WSRT). The Radio Observatory will now assume a major role in maximising the scientific return from LOFAR, closely interacting with the international astronomical community and other users of the LOFAR infrastructure. After this summer, ASTRON’s technical development team will hand over responsibility for the first LOFAR Station (CS01) to the Radio Observatory. Nineteen similar stations are to be deployed over the coming 18 months, and astronomical observations will increasingly ramp-up as each station comes on-line.

Caption: On the 14th June 2007 6 HBA tiles of the LOFAR CS1 station were pointed at the zenith as the radio pulsar B0329+54 passed overhead. The signals from the antennas were added incoherently and the source was observed for 15 minutes while it remained completely in the beam. A total of 48 sub-bands, each of 0.15625 MHz wide, were collected in the frequency range 170-230 MHz. The left hand plot shows the frequency versus pulse phase. The pulsar is seen in almost all sub-bands and displays the expected change in arrival time due to dispersion in the interstellar medium (the properties of the interstellar medium between the pulsar and the earth give rise to different path lengths at different frequencies). The total dispersion delay across this frequency range is about 1.8 seconds or 2.5 pulse periods. Only a few sub-bands are affected by interference.
The right hand plot shows the sum of all sub-bands after correction for the effects of dispersion and shows an excellent signal to noise. We note that this detection uses only 2.5% of a single station's collecting area!

Thanks to the LOFAR Team and all those responsible for the design and construction of LOFAR.
Pulsar observations were carried out by Ben Stappers en Karuppusamy Ramesh (ASTRON and University of Amsterdam).


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.



ASTRON: Prof. Mike Garrett, ASTRON General Director, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo; Tel: 0521-595 100 of 0521-595 119; e-mail: garrett [at] astron [dot] nl (garrett [at] astron [dot] nl)

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

Marjan Tibbe, PR & Communicatie, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo Phone: 0521- 595 162 of 0521- 595 100. e-mail: tibbe [at] astron [dot] nl (tibbe [at] astron [dot] nl).

ASTRON initiated LOFAR as a new and innovative effort to force a breakthrough in sensitivity for astronomical observations at radio-frequencies below 250 MHz. 
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