| 1. |
- Bonardi, A., et al.
(författare)
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Study of the LOFAR radio self-trigger and single-station acquisition mode
- 2018
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Ingår i: 35th International Cosmic Ray Conference, ICRC 2017, 10-20 July 2017. - : Sissa Medialab Srl.
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Konferensbidrag (refereegranskat)abstract
- The LOw Frequency ARay (LOFAR) observatory is a multipurpose radio antenna array aimed to detect radio signals in the frequency range 10-240 MHz. Radio antennas are clustered into over 50 stations, and are spread along Central and Northern Europe. The LOFAR core, where the density of stations is highest, is instrumented with the LOfar Radboud air shower Array (LORA), covering an area of about 300 m diameter centered at the LOFAR core position. Since 2011 the LOFAR core has been used for detecting radio-signals associated to cosmic-ray air showers in the energy range 1016 - 1018 eV. Data acquisition is triggered by the LORA scintillator array, which provides energy, arrival direction, and core position estimates of the detected air shower too. Thus only the core of the LOFAR array is currently used for cosmic-ray detection. In order to extend the energy range of the detected cosmic rays, it is necessary to expand the effective collecting area to the whole LOFAR array. On this purpose, a detailed study about the LOFAR potentialities of working in self-trigger mode, i.e. with the cosmic-ray data acquisition trigger provided by the radio-antenna only, is presented here. A new method based on the intensity and the frequency spectrum for determining the air shower position to be implemented on LOFAR remote stations is presented too. © 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).
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| 2. |
- Buitink, S., et al.
(författare)
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Cosmic ray mass composition with LOFAR
- 2018
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Ingår i: 35th International Cosmic Ray Conference — ICRC2017. 10–20 July, 2017. Bexco, Busan, Korea. - Trieste, Italy : Sissa Medialab Srl.
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Konferensbidrag (refereegranskat)abstract
- The LOFAR radio telescope measures the radio emission from extensive air showers with unprecedented precision. In the dense core individual air showers are detected by hundreds of dipole antennas. By fitting the complex radiation pattern to Monte Carlo radio simulation codes we obtain measurements of the atmospheric depth of the shower maximum X max with a precision of < 20 g/cm 2 . This quantity is sensitive to the mass composition of cosmic rays. We discuss the first mass composition results of LOFAR and the improvements that are currently being made to enhance the accuracy of future analysis. Firstly, a more realistic treatment of the atmosphere will decrease the systematic uncertainties due to the atmosphere. Secondly, a series of upgrades to the LOFAR system will lead to increased effective area, duty cycle, and the possibility to extend the composition analysis down to the energy of 10 16.5 eV. © 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).
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| 3. |
- Corstanje, A., et al.
(författare)
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The effect of the atmospheric refractive index on the radio signal of extensive air showers using Global Data Assimilation System (GDAS)
- 2018
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Ingår i: 35th International Cosmic Ray Conference, ICRC 2017, 10-20 July 2017, Bexco, Busan, Korea. - : Sissa Medialab Srl.
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Konferensbidrag (refereegranskat)abstract
- One of the major systematic uncertainties in the measurement of Xmax from radio emission of EAS arises from variations of the refractive index in the atmosphere. The refractive index n varies with temperature, humidity and pressure, and the variations can be on the order of 10% for (n-1) at a given altitude. The effect of a varying refractive index on Xmax measurements is evaluated using CoREAS: a microscopic simulation of the radio emission from the individual particles in the cascade simulated with CORSIKA. We discuss the resulting offsets in Xmax for different frequency regimes, and compare them to a simple physical model. Under typical circumstances, the offsets in Xmax range from 4-11 g/cm2 for the 30-80 MHz frequency band. Therefore, for precise measurements it is required to include atmospheric data at the time and place of observation of the air shower into the simulations. The aim is to implement this in the next version of CoREAS/CORSIKA using the Global Data Assimilation System (GDAS), a global atmospheric model based on meteorological measurements and numerical weather predictions. This can then be used to re-evaluate the air shower measurements of the LOFAR radio telescope. © 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).
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| 4. |
- Mulrey, K., et al.
(författare)
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Expansion of the LOFAR radboud air shower array
- 2018
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Ingår i: Proceedings of Science. - : Sissa Medialab Srl.
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Konferensbidrag (refereegranskat)abstract
- The LOFAR Radboud Air Shower Array (LORA) consists of 20 plastic scintillators and is situated at the core of the LOFAR radio telescope. LORA detects particles from extensive air showers and triggers the read-out of the LOFAR antennas. The dense LOFAR antenna spacing allows for detailed sampling of the radio emission generated in extensive air showers, which yields high precision reconstruction of cosmic ray properties and information about the shower development. We discuss the proposed expansion of LORA, including the addition of scintillator units and the implementation of triggering algorithms that will probe more details of the radio emission and detect lower energy showers without introducing a composition bias, which is important for studying the origin of cosmic rays.
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| 5. |
- Rossetto, L., et al.
(författare)
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Characterisation of the radio frequency spectrum emitted by high energy air showers with LOFAR
- 2018
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Ingår i: 35th International Cosmic Ray Conference, ICRC2017. - Trieste : Sissa Medialab Srl.
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Konferensbidrag (refereegranskat)abstract
- 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).
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| 6. |
- Winchen, Tobias, et al.
(författare)
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Overview and status of the lunar detection of cosmic particles with LOFAR
- 2018
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Ingår i: Proceedings of Science. - Trieste, Italy : Sissa Medialab Srl.
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Konferensbidrag (refereegranskat)abstract
- 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).
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