Detecting cosmic rays with the LOFAR radio telescope

Schellart, P.; Nelles, A.; Buitink, S.; Corstanje, A.; Enriquez, J. E.; Falcke, H.; Frieswijk, W.; Hörandel, J. R.; Horneffer, A.; James, C. W.; Krause, M.; Mevius, M.; Scholten, Olaf; Veen, S. ter; Thoudam, Satyendra; Akker, M. van den; Alexov, A.; Anderson, J. M.; Avruch, I. M.; Bähren, L.; Beck, Rainer; Bell, M. E.; Bennema, P.; Bentum, Mark J.; Bernardi, G.; Best, P. N.; Bregman, Joel N.; Breitling, F.; Brentjens, M. A.; Broderick, J. W.; Brüggen, M.; Ciardi, B.; Coolen, A. H. W. M.; Gasperin, F. de; Geus, E. de; Jong, A. de; Vos, M. de; Duscha, S.; Eislöffel, J.; Fallows, R. A.; Ferrari, C.; Garrett, M. A.; Grießmeier, J.-M.; Grit, T.; Hamaker, J. P.; Hassall, T. E.; Heald, G.; Hessels, J. W. T.; Hoeft, M.; Holties, H. A.; Iacobelli, M.; Juette, E.; Karastergiou, A.; Klijn, Wouter; Köhler, Jana; Kondratiev, V. I.; Krämer, M.; Kuniyoshi, M.; Küper, G.; Maat, P.; Macario, G.; Mann, G.; Markoff, Sera; McKay-Bukowski, D.; McKean, J. P.; Miller-Jones, J. C. A.; Mol, Jan David; Mulcahy, D. D.; Munk, H.; Nijboer, R.; Norden, M. J.; Orrù, E.; Overeem, R.; Paas, H.; Pandey-Pommier, M.; Pizzo, R.; Polatidis, A. G.; Renting, A.; Romein, John W.; Röttgering, H. J. A.; Schoenmakers, A. P.; Schwarz, Dominik J.; Sluman, J.; Smirnov, O.; Sobey, C.; Stappers, B. W.; Steinmetz, Matthias; Swinbank, J.; Tang, Y.; Tasse, C.; Toribio, C.; Leeuwen, J. van; Nieuwpoort, Rob V. van; Weeren, R. J. van; Vermaas, N. J.; Vermeulen, R. C.; Vocks, C.; Vogt, C.; Wijers, R. A. M. J.; Wijnholds, Stefan J.; Wise, Michael; Wucknitz, O.; Yatawatta, S.; Zarka, Philippe; Zensus, J. A.

doi:10.1051/0004-6361/201322683

Cited by 143 publications

(179 citation statements)

References 18 publications

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“…Observations were made with the Low Frequency Array (LOFAR 13 ), a radio telescope consisting of thousands of crossed dipoles, with built-in air shower detection capability 14 . LOFAR records the radio signals from air showers continuously while running astronomical observations simultaneously.…”

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confidence: 99%

A large light-mass component of cosmic rays at 1017–1017.5 electronvolts from radio observations

Buitink

Corstanje

Falcke

et al. 2016

Nature

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153

149

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4Cosmic rays are the highest energy particles found in nature. Measurements of the mass composition of cosmic rays between 10 17 eV and 10 18 eV are essential to understand whether this energy range is dominated by Galactic or extragalactic sources. It has also been proposed that the astrophysical neutrino signal 1 comes from accelerators capable of producing cosmic rays of these energies 2 . Cosmic rays initiate cascades of secondary particles (air showers) in the atmosphere and their masses are inferred from measurements of the atmospheric depth of the shower maximum, X max 3 , or the composition of shower particles reaching the ground 4 .Current measurements 5 suffer from either low precision, and/or a low duty cycle. Radio detection of cosmic rays 6-8 is a rapidly developing technique 9 , suitable for determination of X max 10, 11 with a duty cycle of in principle nearly 100%. The radiation is generated by the separation of relativistic charged particles in the geomagnetic field and a negative charge excess in the shower front 6, 12 . Here we report radio measurements of X max with a mean precision of 16 g/cm 2 between 10 17 − 10 17.5 eV. Because of the high resolution in X max we can determine the mass spectrum and find a mixed composition, containing a light mass fraction of ∼ 80%. Unless the extragalactic component becomes significant already below 10 17.5 eV, our measurements indicate an additional Galactic component dominating at this energy range.Observations were made with the Low Frequency Array (LOFAR 13 ), a radio telescope consisting of thousands of crossed dipoles, with built-in air shower detection capability 14 . LOFAR records the radio signals from air showers continuously while running astronomical observations simultaneously. It comprises a scintillator array (LORA), that triggers the readout of buffers, stor-5 ing the full waveforms received by all antennas.We have selected air showers from the period June 2011 -January 2015 with radio pulses in at least 192 antennas. The total uptime was ∼150 days, limited by construction and commissioning of the telescope. Showers that occurred within an hour from lightning activity, or have a polarisation pattern that is indicative of influences from atmospheric electric fields are excluded from the sample 15 .Radio intensity patterns from air showers are asymmetric due to the interference between geomagnetic and charge excess radiation. They can be reproduced from first principles by summing the radio contributions of all electrons and positrons in the shower. We use the radio simulation code CoREAS 16 , a plug-in of CORSIKA 17 , which follows this approach.It has been shown that X max can be accurately reconstructed from densely sampled radio measurements 18 . We use a hybrid approach, simultaneously fitting the radio and particle data. The radio component is very sensitive to X max , while the particle component is used for the energy measurement.The fit contains four free parameters: the shower core position (x, y), and scaling factors for the partic...

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confidence: 99%

A large light-mass component of cosmic rays at 1017–1017.5 electronvolts from radio observations

Buitink

Corstanje

Falcke

et al. 2016

Nature

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153

149

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“…In routine observations, coincidences of several particle detectors trigger a read-out 1 Field programmable gate array. of the ring buffers [18].…”

Section: The Instrumentmentioning

confidence: 99%

“…Especially an emergency pager signal at around 170 MHz adds a non-negligible amount of power to the spectrum. Therefore, before additional RFI removal is applied [18], all power in a band of 3 MHz around the pager frequency is set to zero with the edges convolved with a Gaussian to prevent artificial ringing in the signal.…”

Section: Removal Of Radio Frequency Interference (Rfi)mentioning

confidence: 99%

Measuring a Cherenkov ring in the radio emission from air showers at 110–190MHz with LOFAR

Nelles

Schellart

Buitink

et al. 2015

Astroparticle Physics

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Measuring radio emission from air showers offers a novel way to determine properties of the primary cosmic rays such as their mass and energy. Theory predicts that relativistic time compression effects lead to a ring of amplified emission which starts to dominate the emission pattern for frequencies above ∼ 100 MHz. In this article we present the first detailed measurements of this structure. Ring structures in the radio emission of air showers are measured with the LOFAR radio telescope in the frequency range of 110 − 190 MHz. These data are well described by CoREAS simulations. They clearly confirm the importance of including the index of refraction of air as a function of height. Furthermore, the presence of the Cherenkov ring offers the possibility for a geometrical measurement of the depth of shower maximum, which in turn depends on the mass of the primary particle.

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“…For the fit, the reconstructed pulses are integrated in time over a window of 55 ns [17]. They are then summed over all three reconstruction polarisations to obtain a total energy density.…”

Section: Parameterization and Its Applicabilitymentioning

confidence: 99%

“…In the standard LOFAR reconstruction, the results from the fit of this function are used to determine all essential air shower parameters [17,14].…”

Section: Reconstruction Of Air Shower Parametersmentioning

confidence: 99%

A lateral distribution function for the radio emission of air showers

Nelles¹,

Buitink²,

Corstanje³

et al. 2016

Proceedings of the 34th International Cosmic Ray Conference — PoS(ICRC2015)

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The international LOFAR radio telescope has been used now for four years to detect air showers. Its high antenna density has allowed us to measure the subtle features of the radio emission of air showers. Together with air shower simulations, these data have been used to model the detected signals. The not rotational symmetric footprint is described by an analytical function with as few as four free parameters. The parameters are related to the position of the shower axis, the energy and the distance to the shower maximum. We will show how this parametrization is used for a fast reconstruction of all relevant air shower parameters and what accuracies are obtained in comparison to a full Monte Carlo simulation. We will furthermore elaborate on the absolute scale of our measurements and the predicted signal strengths. PoS(ICRC2015)376A lateral distribution function for the radio emission of air showers A. Nelles The left axis belongs to the red squares that depict the measured particle signals, while the blue circle belong to the right axes and show the radio energy density. Also indicated is a typical detection threshold for both particle and radio measurements, which allows to compare the fall-off of the two distributions.

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Detecting cosmic rays with the LOFAR radio telescope

Cited by 143 publications

References 18 publications

A large light-mass component of cosmic rays at 1017–1017.5 electronvolts from radio observations

A large light-mass component of cosmic rays at 1017–1017.5 electronvolts from radio observations

Measuring a Cherenkov ring in the radio emission from air showers at 110–190MHz with LOFAR

A lateral distribution function for the radio emission of air showers

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