10 years of LOFAR highlights: A complete image of the visible sky every second

The behaviour of black holes and neutron stars can expose some of the most extreme tests of physical law. Therefore, this behaviour can be used to find answers to questions as to how black holes are born and to the origin of magnetic fields and cosmic rays. To be able to observe these extreme and transient objects, one must not only survey large areas of sky, but also do this quickly and often. But how do you do this?

Published by the editorial team, 10 June 2020

Project AARTFAAC (Amsterdam-ASTRON Radio Transients Facility And Analysis Center) is a real-time transient detector. It utilizes 576 LOFAR antennae to create an image of the visible sky every second.

AARTFAAC creates images of the low frequency radio sky with a spatial resolution of 10 arcseconds. AARTFAAC is able to quickly create sky images. The clever thing is that AARTFAAC does this simultaneously with, but independently from observations with LOFAR.

Each second the data of 576 LOFAR antennae are collected at a GPU correlator, consisting of 20 GPUs (graphic processor units). There, the data are combined (correlated) with each other.  Next. the correlated data are calibrated, and transformed into sky images. Then, specially developed software analyses these images to determine whether there are so-called transients – sudden changes – present between them. These transients could point to the aforementioned transient objects.

Principal investigator and spiritual father of AARTFAAC is prof. Ralph A.M.J. Wijers from the University of Amsterdam. AARTFAAC is a collaboration of ASTRON (development of Uniboard correlators, co-development of software and science exploitation) and Oxford Astrophysics/e-Research Centre (station hardware development, co-operation on streaming data pipeline) and primarily an experimental system, which has taught astronomers how to build such an all-sky instrument.

LOFAR can create far more detailed images than AARTFAAC can. It uses far more antennae and observes through a far larger bandwidth than AARTFAAC does. But where LOFAR only can capture a small piece of the visible sky simultaneously, AARTFAAC captures the entire visible sky in a single second.

AARTFAAC has a live stream, which you can follow here.

On 12 June 2020, LOFAR celebrates its tenth anniversary. The radio telescope is the world’s largest low frequency instrument and is one of the pathfinders of the Square Kilometre Array (SKA), which is currently being developed. Throughout its ten years of operation, LOFAR has made some amazing discoveries. It has been a key part of groundbreaking research, both in astronomy and engineering. Here we feature some – but definitely not all – of these past highlights, with surely more to come in the future.


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Daily image of the week

On June 13-17, the LOFAR Family Meeting took place in Cologne. After two years LOFAR researchers could finally meet in person again. The meeting brings together LOFAR users and researchers to share new scientific results.

Our renewed ‘Melkwegpad’ (Milky Way Path) is finished! The new signs have texts in Dutch on the one side and in English on the other side. The signs concerning planets have a small, 3D printed model of that planet in their centre.
#Melkwegpad @RTVDrenthe

Daily image of the week

The background drawing shows how the subband correlator calculates the array correlation matrix. In the upper left the 4 UniBoard2s we used. The two ACM plots in the picture show that the phase differences of the visibilities vary from 0 to 360 degrees.

Daily image of the week: Testing with the Dwingeloo Test Station (DTS)
One of the key specifications of LOFAR2.0 is measuring using the low- and the highband antenna at the same time. For this measurement we used 9 lowband antenna and 3 HBA tiles.