10 years of LOFAR highlights: A large light-mass component of cosmic rays at 1017-1017.5 eV from radio observations

By Sander ter Veen

LOFAR is a highly flexible instrument, which can be utilized for many things. Each antenna, for example, has a 5-second buffer, which can be used to measure very short, strong signals. With this attribute from LOFAR, scientists study cosmic radiation, elementary parts, such as protons and iron cores with high amounts of energy, which are approaching earth.

Published by the editorial team, 11 June 2020

One such particle has so much energy that with E = mc2 many other particles are formed. This is what we call a particle shower. In the earth’s magnetic field these particles produce radio waves that can be detected with LOFAR over a surface with a radius of several hundred metres.

The LOFAR Radboud air shower array measures these particles and sends a signal to LOFAR to read out the radio data. Therefore, LOFAR measures these radio waves at different locations. By comparing simulations of the particle shower with the actual measurements the energy and type of particle can be determined. This article describes which parts, containing which amounts of energy are reaching earth and measures that 80% of the particles at 0.3 EeV are a mixture of light parts, such as hydrogen, helium and carbon. The explanation for this, given here is that such a thing as galactic super accelerators exist, for example Wolf-Rayet stars, 500,000 times stronger than the Large Hadron Collider at CERN.

The figure above shows a simulation using LOFAR data. The colour represents the clarity of the radio signal. In the circles the colour indicates the antenna signal, which matches the simulation nicely.

Article referenced: A large light-mass component of cosmic rays at 1017-1017.5 electronvolts from radio observations
DOI: 10.1038/nature16976

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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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

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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.