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Mulrey, K., Bonardi, A., Buitink, S., Corstanje, A., Falcke, H., Hare, B. M., . . . Winchen, T. (2019). Calibration of the LOFAR low-band antennas using the Galaxy and a model of the signal chain. Astroparticle physics, 111, 1-11
Open this publication in new window or tab >>Calibration of the LOFAR low-band antennas using the Galaxy and a model of the signal chain
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2019 (English)In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 111, p. 1-11Article in journal (Refereed) Published
Abstract [en]

The LOw-Frequency ARray (LOFAR) is used to make precise measurements of radio emission from extensive air showers, yielding information about the primary cosmic ray. Interpreting the measured data requires an absolute and frequency-dependent calibration of the LOFAR system response. This is particularly important for spectral analyses, because the shape of the detected signal holds information about the shower development. We revisit the calibration of the LOFAR antennas in the range of 30-80 MHz. Using the Galactic emission and a detailed model of the LOFAR signal chain, we find an improved calibration that provides an absolute energy scale and allows for the study of frequency dependent features in measured signals. With the new calibration, systematic uncertainties of 13% are reached, and comparisons of the spectral shape of calibrated data with simulations show promising agreement. (C) 2019 Elsevier B.V. All rights reserved.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Radio antenna array, Calibration, Air showers
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
urn:nbn:se:lnu:diva-85846 (URN)10.1016/j.astropartphys.2019.03.004 (DOI)000470047300001 ()
Available from: 2019-06-25 Created: 2019-06-25 Last updated: 2019-06-25Bibliographically approved
Winchen, T., Bonardi, A., Buitink, S., Corstanje, A., Falcke, H., Hare, B. M., . . . Trinh, T. N. (2019). Cosmic ray physics with the LOFAR radio telescope. In: Journal of Physics: Conference Series. Paper presented at 26th Extended European Cosmic Ray Symposium, E+CRS 2018, 6 July 2018 through 10 July 2018. Institute of Physics Publishing (1)
Open this publication in new window or tab >>Cosmic ray physics with the LOFAR radio telescope
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2019 (English)In: Journal of Physics: Conference Series, Institute of Physics Publishing , 2019, no 1Conference paper (Refereed)
Abstract [en]

The LOFAR radio telescope is able to measure the radio emission from cosmic ray induced air showers with hundreds of individual antennas. This allows for precision testing of the emission mechanisms for the radio signal as well as determination of the depth of shower maximum X max , the shower observable most sensitive to the mass of the primary cosmic ray, to better than 20 g cm -2 . With a densely instrumented circular area of roughly 320 m 2 , LOFAR is targeting for cosmic ray astrophysics in the energy range 10 16 -10 18 eV. In this contribution we give an overview of the status, recent results, and future plans of cosmic ray detection with the LOFAR radio telescope. © Published under licence by IOP Publishing Ltd.

Place, publisher, year, edition, pages
Institute of Physics Publishing, 2019
Keywords
Cosmic ray detectors, Cosmology, Radio telescopes, Air showers, Emission mechanism, Energy ranges, Radio emission, Radio signals, Cosmic rays
Identifiers
urn:nbn:se:lnu:diva-86424 (URN)10.1088/1742-6596/1181/1/012020 (DOI)2-s2.0-85064343283 (Scopus ID)
Conference
26th Extended European Cosmic Ray Symposium, E+CRS 2018, 6 July 2018 through 10 July 2018
Note

Conference code: 146680; Export Date: 22 May 2019; Conference Paper

Available from: 2019-07-11 Created: 2019-07-11 Last updated: 2019-07-11
Winchen, T., Bonardi, A., Buitink, S., Corstanje, A., Falcke, H., Hare, B. M., . . . Trinh, T. N. (2019). Status of the lunar detection mode for cosmic particles of LOFAR. In: Journal of Physics: Conference Series. Paper presented at 26th Extended European Cosmic Ray Symposium, E+CRS 2018, 6 July 2018 through 10 July 2018. Institute of Physics Publishing (1)
Open this publication in new window or tab >>Status of the lunar detection mode for cosmic particles of LOFAR
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2019 (English)In: Journal of Physics: Conference Series, Institute of Physics Publishing , 2019, no 1Conference paper (Refereed)
Abstract [en]

Cosmic particles hitting Earth's moon produce radio emission via the Askaryan effect. If the resulting radio ns-pulse can be detected by radio telescopes, this technique potentially increases the available collective area for ZeV scale particles by several orders of magnitude compared to current experiments. The LOw Frequency ARray (LOFAR) is the largest radio telescope operating in the optimum frequency regime for this technique. In this contribution, we report on the status of the implementation of the lunar detection mode at LOFAR. © Published under licence by IOP Publishing Ltd.

Place, publisher, year, edition, pages
Institute of Physics Publishing, 2019
Keywords
Cosmic rays, Moon, Radio telescopes, Askaryan effects, Cosmic particles, Detection mode, Low frequency arrays, Optimum frequency, Orders of magnitude, Radio emission, Cosmology
Identifiers
urn:nbn:se:lnu:diva-86425 (URN)10.1088/1742-6596/1181/1/012077 (DOI)2-s2.0-85064332178 (Scopus ID)
Conference
26th Extended European Cosmic Ray Symposium, E+CRS 2018, 6 July 2018 through 10 July 2018
Note

Conference code: 146680; Export Date: 22 May 2019; Conference Paper

Available from: 2019-07-11 Created: 2019-07-11 Last updated: 2019-07-11
Hare, B. M., Scholten, O., Bonardi, A., Buitink, S., Corstanje, A., Ebert, U., . . . Winchen, T. (2018). LOFAR Lightning Imaging: Mapping Lightning With Nanosecond Precision. Journal of Geophysical Research - Atmospheres, 123(5), 2861-2876
Open this publication in new window or tab >>LOFAR Lightning Imaging: Mapping Lightning With Nanosecond Precision
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2018 (English)In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 123, no 5, p. 2861-2876Article in journal (Refereed) Published
Abstract [en]

Lightning mapping technology has proven instrumental in understanding lightning. In this work we present a pipeline that can use lightning observed by the LOw-Frequency ARray (LOFAR) radio telescope to construct a 3-D map of the flash. We show that LOFAR has unparalleled precision, on the order of meters, even for lightning flashes that are over 20km outside the area enclosed by LOFAR antennas (approximate to 3,200km(2)), and can potentially locate over 10,000 sources per lightning flash. We also show that LOFAR is the first lightning mapping system that is sensitive to the spatial structure of the electrical current during individual lightning leader steps.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2018
Keywords
lightning, lightning mapping, LOFAR, time of arrival, leader propagation
National Category
Physical Sciences
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:lnu:diva-72691 (URN)10.1002/2017JD028132 (DOI)000428437100028 ()
Available from: 2018-04-13 Created: 2018-04-13 Last updated: 2019-02-27Bibliographically approved
Arias, M., Vink, J., de Gasperin, F., Salas, P., Oonk, J. B., van Weeren, R. J., . . . Zucca, P. (2018). Low-frequency radio absorption in Cassiopeia A. Astronomy and Astrophysics, 612, Article ID A110.
Open this publication in new window or tab >>Low-frequency radio absorption in Cassiopeia A
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2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 612, article id A110Article in journal (Refereed) Published
Abstract [en]

Context. Cassiopeia A is one of the best-studied supernova remnants. Its bright radio and X-ray emission is due to shocked ejecta. Cas A is rather unique in that the unshocked ejecta can also be studied: through emission in the infrared, the radio-active decay of Ti-44, and the low-frequency free-free absorption caused by cold ionised gas, which is the topic of this paper. Aims. Free-free absorption processes are affected by the mass, geometry, temperature, and ionisation conditions in the absorbing gas. Observations at the lowest radio frequencies can constrain a combination of these properties. Methods. We used Low Frequency Array (LOFAR) Low Band Antenna observations at 30-77 MHz and Very Large Array (VLA) L-band observations at 1-2 GHz to fit for internal absorption as parametrised by the emission measure. We simultaneously fit multiple UV-matched images with a common resolution of 17 '' (this corresponds to 0.25 pc for a source at the distance of Cas A). The ample frequency coverage allows us separate the relative contributions from the absorbing gas, the unabsorbed front of the shell, and the absorbed back of the shell to the emission spectrum. We explored the effects that a temperature lower than the similar to 100-500 K proposed from infrared observations and a high degree of clumping can have on the derived physical properties of the unshocked material, such as its mass and density. We also compiled integrated radio flux density measurements, fit for the absorption processes that occur in the radio band, and considered their effect on the secular decline of the source. Results. We find a mass in the unshocked ejecta of M = 2.95 +/- 0.48 M-circle dot for an assumed gas temperature of T = 100 K. This estimate is reduced for colder gas temperatures and, most significantly, if the ejecta are clumped. We measure the reverse shock to have a radius of 114 '' +/- 6 '' and be centred at 23:23:26, +58:48:54 (J2000). We also find that a decrease in the amount of mass in the unshocked ejecta (as more and more material meets the reverse shock and heats up) cannot account for the observed low-frequency behaviour of the secular decline rate. Conclusions. To reconcile our low-frequency absorption measurements with models that reproduce much of the observed behaviour in Cas A and predict little mass in the unshocked ejecta, the ejecta need to be very clumped or the temperature in the cold gas needs to be low (similar to 10 K). Both of these options are plausible and can together contribute to the high absorption value that we find.

Place, publisher, year, edition, pages
EDP Sciences, 2018
Keywords
supernovae: individual: Cas A, ISM: supernova remnants, radiation mechanisms: general, radio continuum: general
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
urn:nbn:se:lnu:diva-76769 (URN)10.1051/0004-6361/201732411 (DOI)000431715700003 ()
Available from: 2018-07-11 Created: 2018-07-11 Last updated: 2019-07-09Bibliographically approved
Winchen, T., Bonardi, A., Buitink, S., Corstanje, A., Falcke, H., Hare, B. M., . . . Trinh, T. N. (2018). Overview and status of the lunar detection of cosmic particles with LOFAR. In: Proceedings of Science: 35th International Cosmic Ray Conference, ICRC 2017; Bexco, Busan; South Korea; 10-20 July 2017. Paper presented at 35th International Cosmic Ray Conference, ICRC 2017, 10 July 2017 through 20 July 2017. Sissa Medialab Srl
Open this publication in new window or tab >>Overview and status of the lunar detection of cosmic particles with LOFAR
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2018 (English)In: Proceedings of Science: 35th International Cosmic Ray Conference, ICRC 2017; Bexco, Busan; South Korea; 10-20 July 2017, Sissa Medialab Srl , 2018Conference paper, Published paper (Refereed)
Abstract [en]

When a cosmic particle hits matter it produces radio emission via the Askaryan effect. This allows to use Earth's moon as detector for cosmic particles by searching for these ns-pulses with radio telescopes. This technique potentially increases the available collective area by several orders of magnitude compared to current experiments. The LOw Frequency ARray (LOFAR) is the largest radio telescope operating in the optimum frequency regime for corresponding searches. In this contribution, we report on the design and status of the implementation of the lunar detection mode at LOFAR. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives 4.0 International License (CC BY-NC-ND 4.0).

Place, publisher, year, edition, pages
Sissa Medialab Srl, 2018
Keywords
Cosmic rays, Moon, Radio telescopes, Askaryan effects, Cosmic particles, Detection mode, Low frequency arrays, Optimum frequency, Orders of magnitude, Radio emission, Cosmology
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
urn:nbn:se:lnu:diva-85132 (URN)10.22323/1.301.1061 (DOI)2-s2.0-85046060178 (Scopus ID)
Conference
35th International Cosmic Ray Conference, ICRC 2017, 10 July 2017 through 20 July 2017
Available from: 2019-06-12 Created: 2019-06-12 Last updated: 2019-06-13Bibliographically approved
Zucca, P., Morosan, D. E., Rouillard, A. P., Fallows, R., Gallagher, P. T., Magdalenic, J., . . . Zarka, P. (2018). Shock location and CME 3D reconstruction of a solar type II radio burst with LOFAR. Astronomy and Astrophysics, 615, Article ID A89.
Open this publication in new window or tab >>Shock location and CME 3D reconstruction of a solar type II radio burst with LOFAR
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2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 615, article id A89Article in journal (Refereed) Published
Abstract [en]

Context. Type II radio bursts are evidence of shocks in the solar atmosphere and inner heliosphere that emit radio waves ranging from sub-meter to kilometer lengths. These shocks may be associated with coronal mass ejections (CMEs) and reach speeds higher than the local magnetosonic speed. Radio imaging of decameter wavelengths (20-90 MHz) is now possible with the Low Frequency Array (LOFAR), opening a new radio window in which to study coronal shocks that leave the inner solar corona and enter the interplanetary medium and to understand their association with CMEs. Aims. To this end, we study a coronal shock associated with a CME and type II radio burst to determine the locations at which the radio emission is generated, and we investigate the origin of the band-splitting phenomenon. Methods. The type II shock source-positions and spectra were obtained using 91 simultaneous tied-array beams of LOFAR, and the CME was observed by the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory (SOHO) and by the COR2A coronagraph of the SECCHI instruments on board the Solar Terrestrial Relation Observatory (STEREO). The 3D structure was inferred using triangulation of the coronographic observations. Coronal magnetic fields were obtained from a 3D magnetohydrodynamics (MHD) polytropic model using the photospheric fields measured by the Heliospheric Imager (HMI) on board the Solar Dynamic Observatory (SDO) as lower boundary. Results. The type II radio source of the coronal shock observed between 50 and 70 MHz was found to be located at the expanding flank of the CME, where the shock geometry is quasi-perpendicular with theta(Bn)similar to 70 degrees. The type II radio burst showed first and second harmonic emission; the second harmonic source was cospatial with the first harmonic source to within the observational uncertainty. This suggests that radio wave propagation does not alter the apparent location of the harmonic source. The sources of the two split bands were also found to be cospatial within the observational uncertainty, in agreement with the interpretation that split bands are simultaneous radio emission from upstream and downstream of the shock front. The fast magnetosonic Mach number derived from this interpretation was found to lie in the range 1.3-1.5. The fast magnetosonic Mach numbers derived from modelling the CME and the coronal magnetic field around the type II source were found to lie in the range 1.4-1.6.

Place, publisher, year, edition, pages
EDP Sciences, 2018
Keywords
Sun: corona, Sun: coronal mass ejections (CMEs), Sun: radio radiation
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
urn:nbn:se:lnu:diva-77396 (URN)10.1051/0004-6361/201732308 (DOI)000439525400003 ()
Available from: 2018-08-29 Created: 2018-08-29 Last updated: 2019-07-09Bibliographically approved
Thoudam, S., Becherini, Y. & Punch, M. (2018). Simulation study for the proposed wide field-of-view gamma-ray detector array ALTO. In: Proceedings of Science: 35th International Cosmic Ray Conference, ICRC 2017, 10 -20 July 2017, Bexico, South Korea. Paper presented at 35th International Cosmic Ray Conference, ICRC 2017, 10 -20 July 2017, Bexico, South Korea. Sissa Medialab Srl
Open this publication in new window or tab >>Simulation study for the proposed wide field-of-view gamma-ray detector array ALTO
2018 (English)In: Proceedings of Science: 35th International Cosmic Ray Conference, ICRC 2017, 10 -20 July 2017, Bexico, South Korea, Sissa Medialab Srl , 2018Conference paper, Published paper (Refereed)
Abstract [en]

ALTO is a wide field-of-view air shower detector array for very-high-energy (VHE) gamma-ray astronomy, proposed to be installed in the Southern Hemisphere at an altitude of ∼5.1 km above sea level. The array will use water Cherenkov detectors, as in the HAWC observatory, but combined with scintillator detectors, to detect air showers induced by VHE gamma rays in the atmosphere. It is being designed to attain a lower energy threshold, better energy and angular resolution, and improved sensitivity. The array will consist of ∼1250 small-sized (3.6 m diameter) detector units distributed over a circular area of ∼160 m in diameter. Each detector unit will consist of a water Cherenkov detector and a liquid scintillation detector underneath which will preferentially identify muons, facilitating the background (cosmic ray) rejection, thereby improving the sensitivity. The background rejection will be further enhanced by the close-packed arrangement and the small size of the detectors which will allow a fine sampling of air-shower footprints at the ground. In this contribution, we present the Monte-Carlo simulation of the experiment performed using CORSIKA and GEANT4 simulation packages. The expected performance of the array in terms of reconstruction accuracies of the shower core and arrival direction, as well as preliminary estimate of the trigger energy threshold after preliminary selection cuts for a point-like gamma-ray source are presented. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives 4.0 International License (CC BY-NC-ND 4.0).

Place, publisher, year, edition, pages
Sissa Medialab Srl, 2018
Keywords
Cerenkov counters, Cosmic rays, Cosmology, Intelligent systems, Monte Carlo methods, Particle detectors, Sea level, Background rejection, Close-packed arrangement, Gamma-ray astronomy, Gamma-ray detector arrays, Reconstruction accuracy, Scintillator detector, Southern Hemisphere, Water Cherenkov detectors, Gamma rays
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
urn:nbn:se:lnu:diva-84356 (URN)10.22323/1.301.0780 (DOI)2-s2.0-85046059785 (Scopus ID)
Conference
35th International Cosmic Ray Conference, ICRC 2017, 10 -20 July 2017, Bexico, South Korea
Available from: 2019-06-11 Created: 2019-06-11 Last updated: 2019-06-13Bibliographically approved
Rossetto, L., Bonardi, A., Buitink, S., Corstanje, A., Falcke, H., Hare, B. M., . . . Winchen, T. (2017). Characterisation of the radio frequency spectrum emitted by high energy air showers with LOFAR. In: Proceedings of Science: . Paper presented at 35th International Cosmic Ray Conference, 12 − 20 July, 2017. Bexco, Busan, Korea (pp. 1-8). Trieste: Sissa Medialab Srl
Open this publication in new window or tab >>Characterisation of the radio frequency spectrum emitted by high energy air showers with LOFAR
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2017 (English)In: Proceedings of Science, Trieste: Sissa Medialab Srl , 2017, p. 1-8Conference paper, Published paper (Refereed)
Abstract [en]

The high number density of radio antennas at the LOFAR core in Northern Netherlands allows to detect radio signals emitted by extensive air showers in the energy range 1016 - 1018 e V, and to characterise the geometry of the observed cascade in a detailed way. The radio signal emitted by extensive air showers along their propagation in the atmosphere has been studied in the 30 - 70 MHz frequency range. The study has been conducted on real data and simulated showers. Regarding real data, cosmic ray radio signals detected by LOFAR since 2011 have been analysed. For simulated showers, the CoREAS code, a plug-in of the CORSIKA particle simulation code, has been used. The results show a clear dependence of the frequency spectrum on the distance to the shower axis for both real data and simulations. In particular, the spectrum flatten at a distance around 100 m from the shower axis, where the coherence of the radio signal is maximum. This behaviour could also be used to reconstruct the position of the shower axis at ground. A correlation between the frequency spectrum and the geometrical distance to the depth of the shower maximum Xmax has also been investigated. The final aim of this study is to find a method to improve the inferred information of primary cosmic rays with radio antennas, in view of affirming the radio detection technique as reliable method for the study of extensive air showers. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives 4.0 International License (CC BY-NC-ND 4.0).

Place, publisher, year, edition, pages
Trieste: Sissa Medialab Srl, 2017
Keywords
Antennas, Cosmology, Signal detection, Spectroscopy, Extensive air showers, Frequency ranges, Frequency spectra, Geometrical distances, Particle simulations, Radio detection, Radio frequency spectrum, Reliable methods, Cosmic rays
Identifiers
urn:nbn:se:lnu:diva-85118 (URN)2-s2.0-85046061201 (Scopus ID)
Conference
35th International Cosmic Ray Conference, 12 − 20 July, 2017. Bexco, Busan, Korea
Note

Conference code: 135186; Export Date: 11 June 2019; Conference Paper

Available from: 2019-07-11 Created: 2019-07-11 Last updated: 2019-07-11
Trinh, T. N., Scholten, O., Bonardi, A., Buitink, S., Corstanje, A., Ebert, U., . . . Winchen, T. (2017). Circular polarization of radio emission from air showers in thunderstorm conditions. In: Buitink, S Horandel, JR DeJong, S Lahmann, R Nahnhauer, R Scholten, O (Ed.), 7th International Conference on Acoustic and Radio EeV Neutrino Detection Activities (ARENA 2016): . Paper presented at 7th International Conference on Acoustic and Radio EeV Neutrino Detection Activities (ARENA), JUN 07-10, 2016, Groningen, NETHERLANDS. E D P SCIENCES, Article ID UNSP 03002.
Open this publication in new window or tab >>Circular polarization of radio emission from air showers in thunderstorm conditions
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2017 (English)In: 7th International Conference on Acoustic and Radio EeV Neutrino Detection Activities (ARENA 2016) / [ed] Buitink, S Horandel, JR DeJong, S Lahmann, R Nahnhauer, R Scholten, O, E D P SCIENCES , 2017, article id UNSP 03002Conference paper, Published paper (Refereed)
Abstract [en]

We present measured radio emission from cosmic-ray-induced air showers under thunderstorm conditions. We observe for these events large differences in intensity, linear polarization and circular polarization from the events measured under fair-weather conditions. This can be explained by the effects of atmospheric electric fields in thunderclouds. Therefore, measuring the intensity and polarization of radio emission from cosmic ray extensive air showers during thunderstorm conditions provides a new tool to probe the atmospheric electric fields present in thunderclouds.

Place, publisher, year, edition, pages
E D P SCIENCES, 2017
Series
EPJ Web of Conferences, ISSN 2100-014X ; 135
National Category
Physical Sciences
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:lnu:diva-79221 (URN)10.1051/epjconf/201713503002 (DOI)000407847700024 ()978-2-7598-9015-6 (ISBN)
Conference
7th International Conference on Acoustic and Radio EeV Neutrino Detection Activities (ARENA), JUN 07-10, 2016, Groningen, NETHERLANDS
Available from: 2018-12-14 Created: 2018-12-14 Last updated: 2019-02-27Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-7066-3614

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