| 1. |
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| 2. |
- Achterberg, A., et al.
(författare)
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Limits on the high-energy gamma and neutrino fluxes from the SGR 1806-20 giant flare of 27 December 2004 with the AMANDA-II detector
- 2006
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 97:22, s. 221101-
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Tidskriftsartikel (refereegranskat)abstract
- On 27 December 2004, a giant gamma flare from the Soft Gamma-Ray Repeater 1806-20 saturated many satellite gamma-ray detectors, being the brightest transient event ever observed in the Galaxy. AMANDA-II was used to search for down-going muons indicative of high-energy gammas and/or neutrinos from this object. The data revealed no significant signal, so upper limits (at 90% C.L.) on the normalization constant were set: 0.05(0.5) TeV-1 m(-2) s(-1) for gamma=-1.47 (-2) in the gamma flux and 0.4(6.1) TeV-1 m(-2) s(-1) for gamma=-1.47 (-2) in the high-energy neutrino flux.
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| 3. |
- Abbasi, R., et al.
(författare)
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Studies of systematic uncertainty effects on IceCube's real-time angular uncertainty
- 2022
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Ingår i: 37th International Cosmic Ray Conference, ICRC2021. - Trieste, Italy : Proceedings of Science.
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Konferensbidrag (refereegranskat)abstract
- Sources of astrophysical neutrinos can potentially be discovered through the detection of neutrinos in coincidence with electromagnetic or gravitational waves. Real-time alerts generated by IceCube play an important role in this search, acting as triggers for follow-up observations with instruments sensitive to other wavelengths. Once a high-energy event is detected by the IceCube real-time program, a complex and time consuming direction reconstruction method is run in order to calculate an accurate localisation. To investigate the effect of systematic uncertainties on the uncertainty estimate of the location, we simulate a set of high-energy events with a wide range of directions for different ice model realisations, the dominant systematic error in our localization uncertainty. This makes use of a novel simulation tool, which allows the treatment of systematic uncertainties with multiple continuously varied nuisance parameters. These events will be reconstructed using various reconstruction methods. This study will enable us to include systematic uncertainties in a robust manner in the real-time direction and error estimates.
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| 4. |
- Achtenhagen, Leona, 1969-, et al.
(författare)
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Upholding the 4th estate—exploring the corporate governance of the media ownership form of business foundations
- 2018
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Ingår i: JMM - The International Journal on Media Management. - : Taylor & Francis. - 1424-1277 .- 1424-1250. ; 20:2, s. 129-150
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Tidskriftsartikel (refereegranskat)abstract
- Whereas media ownership issues have interested scholars for decades, research has largely ignored the implications of specific ownership forms on the corporate governance of media companies, that is, how these companies are directed and controlled. This article attempts to address this gap by exploring the corporate governance of the ownership form of business foundations—a type of ownership that is increasing in different countries around the world. We analyze the corporate governance of three business foundations in the Swedish newspaper sector that together hold 26% of the market and outperform their industry peers. The control function, which is at the heart of corporate governance, is typically performed by companies’ owners. However, foundations do not have a physical person as owner; thus, this control function is replaced by the foundation’s charter, which stipulates the aim of the foundation’s business activities. When steered by professional top management, the charter’s long-term orientation facilitates the careful implementation of strategic directions without short-term performance pressures. We conclude the article by outlining several advantages and disadvantages of this ownership form for the media industry.
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| 5. |
- Abbasi, R., et al.
(författare)
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Search for decoherence from quantum gravity with atmospheric neutrinos
- 2024
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Ingår i: Nature Physics. - 1745-2481 .- 1745-2473. ; 20:6, s. 913-920
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Tidskriftsartikel (refereegranskat)abstract
- Neutrino oscillations at the highest energies and longest baselines can be used to study the structure of spacetime and test the fundamental principles of quantum mechanics. If the metric of spacetime has a quantum mechanical description, its fluctuations at the Planck scale are expected to introduce non-unitary effects that are inconsistent with the standard unitary time evolution of quantum mechanics. Neutrinos interacting with such fluctuations would lose their quantum coherence, deviating from the expected oscillatory flavour composition at long distances and high energies. Here we use atmospheric neutrinos detected by the IceCube South Pole Neutrino Observatory in the energy range of 0.5-10.0 TeV to search for coherence loss in neutrino propagation. We find no evidence of anomalous neutrino decoherence and determine limits on neutrino-quantum gravity interactions. The constraint on the effective decoherence strength parameter within an energy-independent decoherence model improves on previous limits by a factor of 30. For decoherence effects scaling as E2, our limits are advanced by more than six orders of magnitude beyond past measurements compared with the state of the art. Interactions of atmospheric neutrinos with quantum-gravity-induced fluctuations of the metric of spacetime would lead to decoherence. The IceCube Collaboration constrains such interactions with atmospheric neutrinos.
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| 6. |
- Abbasi, R., et al.
(författare)
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Development of a scintillation and radio hybrid detector array at the South Pole
- 2022
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Ingår i: 37th International Cosmic Ray Conference, ICRC2021. - : Proceedings of Science.
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Konferensbidrag (refereegranskat)abstract
- At the IceCube Neutrino Observatory, a Surface Array Enhancement is planned, consisting of 32 hybrid stations, placed within the current IceTop footprint. This surface enhancement will considerably increase the detection sensitivity to cosmic rays in the 100 TeV to 1 EeV primary energy range, measure the effects of snow accumulation on the existing IceTop tanks and serve as R&D for the possible future large-scale surface array of IceCube-Gen2. Each station has one central hybrid DAQ, which reads out 8 scintillation detectors and 3 radio antennas. The radio antenna SKALA-2 is used in this array due to its low-noise, high amplification and sensitivity in the 70-350 MHz frequency band. Every scintillation detector has an active area of 1.5 m(2) organic plastic scintillators connected by wavelength-shifting fibers, which are connected to a silicon photomultiplier. The signals from the scintillation detectors are integrated and digitized by a local custom electronics board and transferred to the central DAQ. When triggered by the scintillation detectors, the filtered and amplified analog waveforms from the radio antennas are read out and digitized by the central DAQ. A full prototype station has been developed and built and was installed at the South Pole in January 2020. It is planned to install the full array by 2026. In this contribution the hardware design of the array as well as the installation plans will be presented.
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| 7. |
- Abbasi, R., et al.
(författare)
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Discrimination of muons for mass composition studies of inclined air showers detected with IceTop
- 2022
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Ingår i: 37th International Cosmic Ray Conference, ICRC2021. - : Proceedings of Science.
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Konferensbidrag (refereegranskat)abstract
- IceTop, the surface array of IceCube, measures air showers from cosmic rays within the energy range of 1 PeV to a few EeV and a zenith angle range of up to approximate to 36 degrees. This detector array can also measure air showers arriving at larger zenith angles at energies above 20 PeV. Air showers from lighter primaries arriving at the array will produce fewer muons when compared to heavier cosmic-ray primaries. A discrimination of these muons from the electromagnetic component in the shower can therefore allow a measurement of the primary mass. A study to discriminate muons using Monte-Carlo air showers of energies 20-100 PeV and within the zenith angular range of 45 degrees-60 degrees will be presented. The discrimination is done using charge and time-based cuts which allows us to select muon-like signals in each shower. The methodology of this analysis, which aims at categorizing the measured air showers as light or heavy on an event-by-event basis, will be discussed.
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| 8. |
- Abbasi, R., et al.
(författare)
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Searching for neutrino transients below 1 TeV with IceCube
- 2022
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Ingår i: 37th International Cosmic Ray Conference (ICRC 2021). - Trieste, Italy : Sissa Medialab Srl.
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Konferensbidrag (refereegranskat)abstract
- Recent observations of GeV gamma-rays from novae have led to a paradigm shift in the understanding of these objects. While it is nowbelieved that shocks contribute significantly to the energy budget of novae, it is still unknown if the emission is hadronic or leptonic in origin. Neutrinos could hold the key to definitively differentiating between these two scenarios, though the energies of such particles would be much lower than are typically targeted with neutrino telescopes. IceCube's densely instrumented DeepCore sub-array provides the ability to reduce the threshold for observation from 1 TeV down to approximately 10 GeV. We will discuss recent measurements in this low energy regime, details of a new sub-TeV selection, and prospects for future searches for transient neutrino emission.
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| 9. |
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| 10. |
- Achterberg, A., et al.
(författare)
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First Year Performance of the IceCube Neutrino Telescope
- 2006
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Ingår i: Astroparticle physics. - : Elsevier BV. - 0927-6505 .- 1873-2852. ; 26:3, s. 155-173
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Tidskriftsartikel (refereegranskat)abstract
- The first sensors of the IceCube neutrino observatory were deployed at the South Pole during the austral summer of 2004-2005 and have been producing data since February 2005. One string of 60 sensors buried in the ice and a surface array of eight ice Cherenkov tanks took data until December 2005 when deployment of the next set of strings and tanks began. We have analyzed these data, demonstrating that the performance of the system meets or exceeds design requirements. Times are determined across the whole array to a relative precision of better than 3 ns, allowing reconstruction of muon tracks and light bursts in the ice, of air-showers in the surface array and of events seen in coincidence by surface and deep-ice detectors separated by up to 2.5 km.
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