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| 2. |
- Buitink, Stijn, et al.
(författare)
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Searching for neutrino radio flashes from the Moon with LOFAR
- 2013
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Ingår i: 5th International Workshop on Acoustic and Radio EeV Neutrino Detection Activities. - : American Institute of Physics (AIP). ; , s. 27-31
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Konferensbidrag (refereegranskat)abstract
- Ultra-high-energy neutrinos and cosmic rays produce short radio flashes through the Askaryan effect when they impact on the Moon. Earthbound radio telescopes can search the Lunar surface for these signals. A new generation of lowfrequency, digital radio arrays, spearheaded by LOFAR, will allow for searches with unprecedented sensitivity. In the first stage of the NuMoon project, low-frequency observations were carried out with the Westerbork Synthesis Radio Telescope, leading to the most stringent limit on the cosmic neutrino flux above 1023 eV. With LOFAR we will be able to reach a sensitivity of over an order of magnitude better and to decrease the threshold energy.
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| 3. |
- Nelles, Anna, et al.
(författare)
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Detecting radio emission from air showers with LOFAR
- 2013
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Ingår i: 5th International Workshop on Acoustic and Radio EeV Neutrino Detection Activities. - : American Institute of Physics (AIP). ; , s. 105-110
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Konferensbidrag (refereegranskat)abstract
- LOFAR (the Low Frequency Array) is the largest radio telescope in the world for observing low frequency radio emission from 10 to 240 MHz. In addition to its use as an interferometric array, LOFAR is now routinely used to detect cosmic ray induced air showers by their radio emission. The LOFAR core in the Netherlands has a higher density of antennas than any dedicated cosmic ray experiment in radio. On an area of 12 km2 more than 2300 antennas are installed. They measure the radio emission from air showers with unprecedented precision and, therefore, give the perfect opportunity to disentangle the physical processes which cause the radio emission in air showers. In parallel to ongoing astronomical observations LOFAR is triggered by an array of particle detectors to record time-series containing cosmic-ray pulses. Cosmic rays have been measured with LOFAR since June 2011. We present the results of the first year of data.
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| 4. |
- Pastor-Marazuela, Ines, et al.
(författare)
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Chromatic periodic activity down to 120 megahertz in a fast radio burst
- 2021
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 596:7873, s. 505-508
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Tidskriftsartikel (refereegranskat)abstract
- Fast radio bursts (FRBs) are extragalactic astrophysical transients(1) whose brightness requires emitters that are highly energetic yet compact enough to produce the short, millisecond-duration bursts. FRBs have thus far been detected at frequencies from 8 gigahertz (ref. (2)) down to 300 megahertz (ref. (3)), but lower-frequency emission has remained elusive. Some FRBs repeat(4-6), and one of the most frequently detected, FRB 20180916B(7), has a periodicity cycle of 16.35 days (ref. (8)). Using simultaneous radio data spanning a wide range of wavelengths (a factor of more than 10), here we show that FRB 20180916B emits down to 120 megahertz, and that its activity window is frequency dependent (that is, chromatic). The window is both narrower and earlier at higher frequencies. Binary wind interaction models predict a wider window at higher frequencies, the opposite of our observations. Our full-cycle coverage shows that the 16.3-day periodicity is not aliased. We establish that low-frequency FRB emission can escape the local medium. For bursts of the same fluence, FRB 20180916B is more active below 200 megahertz than at 1.4 gigahertz. Combining our results with previous upper limits on the all-sky FRB rate at 150 megahertz, we find there are 3-450 FRBs in the sky per day above 50 Jy ms. Our chromatic results strongly disfavour scenarios in which absorption from strong stellar winds causes FRB periodicity. We demonstrate that some FRBs are found in 'clean' environments that do not absorb or scatter low-frequency radiation. The fast radio burst FRB 20180916B repeats with a periodicity of 16 days, and is now found to emit down to a frequency of 120 MHz, much lower than previously observed.
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| 5. |
- Rossetto, Laura, et al.
(författare)
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Latest results on the analysis of the radio frequency spectrum emitted by high energy air showers with LOFAR
- 2019
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Ingår i: 8th International Conference on Acoustic and Radio EeV Neutrino Detection Activities (ARENA 2018). - : EDP Sciences. - 9782759890804 ; , s. 1-3
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Konferensbidrag (refereegranskat)abstract
- The LOw Frequency ARay (LOFAR) is a multi-purpose radio antenna array aimed to detect radio signals in the frequency range 10 - 240 MHz, covering a large surface in Northern Europe with a higher density in the Netherlands. Analytical calculations and simulation studies performed in the 2000s indicate a dependence of the radio frequency spectrum on cosmic-ray characteristics. The high number density of radio antennas at the LOFAR core allows to characterise the observed cascade in a detailed way. The radio signal emitted by air showers in the atmosphere has been studied accurately in the 30 - 80 MHz frequency range. The analysis has been conducted on simulated events and on real data detected by LOFAR since 2011. The final aim of this study is to find an independent method to infer information of primary cosmic rays for improving the reconstruction of primary particle parameters. Results show a strong dependence of the frequency spectrum on the distance to the shower axis for both real data and simulations. Furthermore, results show that this method is very sensitive to the precision in reconstructing the position of the shower axis at ground, and to different antenna calibration procedures. A correlation between the frequency spectrum and geometrical distance to the shower maximum development X-max has also been investigated.
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| 6. |
- Scholten, Olaf, et al.
(författare)
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Lightning Imaging with LOFAR
- 2017
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Ingår i: 7th International Conference on Acoustic and Radio EeV Neutrino Detection Activities (ARENA 2016). - : EDP Sciences.
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Konferensbidrag (refereegranskat)abstract
- We show that LOFAR can be used as a lightning mapping array with a resolution that is orders of magnitude better than existing arrays. In addition the polarization of the radiation can be used to track the direction of the stepping discharges. © 2017 The Authors, published by EDP Sciences.
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| 7. |
- Scholten, Olaf, et al.
(författare)
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Precision study of radio emission from air showers at LOFAR
- 2017
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Ingår i: RICAP16, 6TH ROMA INTERNATIONAL CONFERENCE ON ASTROPARTICLE PHYSICS. - : EDP Sciences.
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Konferensbidrag (refereegranskat)abstract
- Radio detection as well as modeling of cosmic rays has made enormous progress in the past years. We show this by using the subtle circular polarization of the radio pulse from air showers measured in fair weather conditions and the intensity of radio emission from an air shower under thunderstorm conditions.
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| 8. |
- Thomas, HS, et al.
(författare)
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- 2019
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swepub:Mat__t
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