| 61. |
- Abbasi, R., et al.
(author)
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Measurement of the anisotropy of cosmic-ray arrival directions with icecube
- 2010
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In: The Astrophysical Journal Letters. - 2041-8205. ; 718, s. L194-L198
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Journal article (peer-reviewed)abstract
- We report the first observation of an anisotropy in the arrival direction of cosmic rays with energies in the multi-TeV region in the Southern sky using data from the IceCube detector. Between 2007 June and 2008 March, the partially deployed IceCube detector was operated in a configuration with 1320 digital optical sensors distributed over 22 strings at depths between 1450 and 2450 m inside the Antarctic ice. IceCube is a neutrino detector, but the data are dominated by a large background of cosmic-ray muons. Therefore, the background data are suitable for high-statistics studies of cosmic rays in the southern sky. The data include 4.3 billion muons produced by downward-going cosmic-ray interactions in the atmosphere; these events were reconstructed with a median angular resolution of 3 degrees and a median energy of similar to 20 TeV. Their arrival direction distribution exhibits an anisotropy in right ascension with a first-harmonic amplitude of (6.4 +/- 0.2 stat. +/- 0.8 syst.) x 10(-4).
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| 62. |
- Abbasi, R., et al.
(author)
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Neutrino Analysis of the 2010 September Crab Nebula Flare and Time-Integrated Constraints on Neutrino Emission from the Crab Using Icecube
- 2012
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In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 745:1, s. 45-
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Journal article (peer-reviewed)abstract
- We present the results of a search for high-energy muon neutrinos with the IceCube detector in coincidence with the Crab Nebula flare reported on 2010 September by various experiments. Due to the unusual flaring state of the otherwise steady source we performed a prompt analysis of the 79-string configuration data to search for neutrinos that might be emitted along with the observed. gamma-rays. We performed two different and complementary data selections of neutrino events in the time window of 10 days around the flare. One event selection is optimized for discovery of E-upsilon(2). neutrino spectrum typical of first-order Fermi acceleration. A similar event selection has also been applied to the 40-string data to derive the time-integrated limits to the neutrino emission from the Crab. The other event selection was optimized for discovery of neutrino spectra with softer spectral index and TeV energy cutoffs as observed for various Galactic sources in. gamma-rays. The 90% confidence level (CL) best upper limits on the Crab flux during the 10 day flare are 4.73 x 10(-11) cm(-2) s(-1) TeV-1 for an E-upsilon(2). neutrino spectrum and 2.50 x 10(-10) cm(-2) s(-1) TeV-1 for a softer neutrino spectra of E-upsilon(-2.7), as indicated by Fermi measurements during the flare. In this paper, we also illustrate the impact of the time-integrated limit on the Crab neutrino steady emission. The limit obtained using 375.5 days of the 40-string configuration is compared to existing models of neutrino production from the Crab and its impact on astrophysical parameters is discussed. The most optimistic predictions of some models are already rejected by the IceCube neutrino telescope with more than 90% CL.
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| 63. |
- Abbasi, R., et al.
(author)
-
Observation of anisotropy in the arrival directions of galactic cosmic rays at multiple angular scales with IceCube
- 2011
-
In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 740:1, s. 16-
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Journal article (peer-reviewed)abstract
- Between 2009 May and 2010 May, the IceCube neutrino detector at the South Pole recorded 32 billion muons generated in air showers produced by cosmic rays with a median energy of 20 TeV. With a data set of this size, it is possible to probe the southern sky for per-mil anisotropy on all angular scales in the arrival direction distribution of cosmic rays. Applying a power spectrum analysis to the relative intensity map of the cosmic ray flux in the southern hemisphere, we show that the arrival direction distribution is not isotropic, but shows significant structure on several angular scales. In addition to previously reported large-scale structure in the form of a strong dipole and quadrupole, the data show small-scale structure on scales between 15 degrees and 30 degrees. The skymap exhibits several localized regions of significant excess and deficit in cosmic ray intensity. The relative intensity of the smaller-scale structures is about a factor of five weaker than that of the dipole and quadrupole structure. The most significant structure, an excess localized at (right ascension alpha = 122 degrees.4 and declination d = -47 degrees.4), extends over at least 20 degrees in right ascension and has a post-trials significance of 5.3 sigma. The origin of this anisotropy is still unknown.
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| 64. |
- Abbasi, R., et al.
(author)
-
Search for a diffuse flux of astrophysical muon neutrinos with the IceCube 40-string detector
- 2011
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In: Physical Review D. - 1550-7998 .- 1550-2368. ; 84:8, s. 082001-
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Journal article (peer-reviewed)abstract
- The IceCube Neutrino Observatory is a 1 km(3) detector currently taking data at the South Pole. One of the main strategies used to look for astrophysical neutrinos with IceCube is the search for a diffuse flux of high-energy neutrinos from unresolved sources. A hard energy spectrum of neutrinos from isotropically distributed astrophysical sources could manifest itself as a detectable signal that may be differentiated from the atmospheric neutrino background by spectral measurement. This analysis uses data from the IceCube detector collected in its half completed configuration which operated between April 2008 and May 2009 to search for a diffuse flux of astrophysical muon neutrinos. A total of 12 877 upward-going candidate neutrino events have been selected for this analysis. No evidence for a diffuse flux of astrophysical muon neutrinos was found in the data set leading to a 90% C. L. upper limit on the normalization of an E(-2) astrophysical nu(mu) flux of 8.9 x 10(-9) GeV cm(-2) s(-1) sr(-1). The analysis is sensitive in the energy range between 35 TeV and 7 PeV. The 12 877 candidate neutrino events are consistent with atmospheric muon neutrinos measured from 332 GeV to 84 TeV and no evidence for a prompt component to the atmospheric neutrino spectrum is found.
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| 65. |
- Abbasi, R., et al.
(author)
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Search for relativistic magnetic monopoles with the AMANDA-II neutrino telescope
- 2010
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In: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 69:3-4, s. 361-378
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Journal article (peer-reviewed)abstract
- We present the search for Cherenkov signatures from relativistic magnetic monopoles in data taken with the AMANDA-II detector, a neutrino telescope deployed in the Antarctic ice cap at the Geographic South Pole. The non-observation of a monopole signal in data collected during the year 2000 improves present experimental limits on the flux of relativistic magnetic monopoles: Our flux limit varies between 3.8x10(-17) cm(-2) s(-1) sr(-1) (for monopoles moving at the vacuum speed of light) and 8.8x10(-16) cm(-2) s(-1) sr(-1) (for monopoles moving at a speed beta=v/c=0.76, just above the Cherenkov threshold in ice). These limits apply to monopoles that are energetic enough to penetrate the Earth and enter the detector from below the horizon. The limit obtained for monopoles reaching the detector from above the horizon is less stringent by roughly an order of magnitude, due to the much larger background from down-going atmospheric muons. This looser limit is however valid for a larger class of magnetic monopoles, since the monopoles are not required to pass through the Earth.
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| 66. |
- Abbasi, R., et al.
(author)
-
Searching for soft relativistic jets in core-collapse supernovae with the IceCube optical follow-up program
- 2012
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 539, s. A60-
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Journal article (peer-reviewed)abstract
- Context. Transient neutrino sources such as gamma-ray bursts (GRBs) and supernovae (SNe) are hypothesized to emit bursts of high-energy neutrinos on a time-scale of less than or similar to 100 s. While GRB neutrinos would be produced in high relativistic jets, core-collapse SNe might host soft-relativistic jets, which become stalled in the outer layers of the progenitor star leading to an efficient production of high-energy neutrinos. Aims. To increase the sensitivity to these neutrinos and identify their sources, a low-threshold optical follow-up program for neutrino multiplets detected with the IceCube observatory has been implemented. Methods. If a neutrino multiplet, i.e. two or more neutrinos from the same direction within 100 s, is found by IceCube a trigger is sent to the Robotic Optical Transient Search Experiment, ROTSE. The 4 ROTSE telescopes immediately start an observation program of the corresponding region of the sky in order to detect an optical counterpart to the neutrino events. Results. No statistically significant excess in the rate of neutrino multiplets has been observed and furthermore no coincidence with an optical counterpart was found. Conclusions. The search allows, for the first time, to set stringent limits on current models predicting a high-energy neutrino flux from soft relativistic hadronic jets in core-collapse SNe. We conclude that a sub-population of SNe with typical Lorentz boost factor and jet energy of 10 and 3 x 1051 erg, respectively, does not exceed 4.2% at 90% confidence.
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| 67. |
- Aartsen, M. G., et al.
(author)
-
Characterization of the atmospheric muon flux in IceCube
- 2016
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In: Astroparticle physics. - : Elsevier BV. - 0927-6505 .- 1873-2852. ; 78, s. 1-27
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Journal article (peer-reviewed)abstract
- Muons produced in atmospheric cosmic ray showers account for the by far dominant part of the event yield in large-volume underground particle detectors. The IceCube detector, with an instrumented volume of about a cubic kilometer, has the potential to conduct unique investigations on atmospheric muons by exploiting the large collection area and the possibility to track particles over a long distance. Through detailed reconstruction of energy deposition along the tracks, the characteristics of muon bundles can be quantified, and individual particles of exceptionally high energy identified. The data can then be used to constrain the cosmic ray primary flux and the contribution to atmospheric lepton fluxes from prompt decays of short-lived hadrons. In this paper, techniques for the extraction of physical measurements from atmospheric muon events are described and first results are presented. The multiplicity spectrum of TeV muons in cosmic ray air showers for primaries in the energy range from the knee to the ankle is derived and found to be consistent with recent results from surface detectors. The single muon energy spectrum is determined up to PeV energies and shows a clear indication for the emergence of a distinct spectral component from prompt decays of short-lived hadrons. The magnitude of the prompt flux, which should include a substantial contribution from light vector meson di-muon decays, is consistent with current theoretical predictions. The variety of measurements and high event statistics can also be exploited for the evaluation of systematic effects. In the course of this study, internal inconsistencies in the zenith angle distribution of events were found which indicate the presence of an unexplained effect outside the currently applied range of detector systematics. The underlying cause could be related to the hadronic interaction models used to describe muon production in air showers.
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| 68. |
- Aartsen, M. G., et al.
(author)
-
Development of a general analysis and unfolding scheme and its application to measure the energy spectrum of atmospheric neutrinos with IceCube
- 2015
-
In: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 75:3
-
Journal article (peer-reviewed)abstract
- We present the development and application of a generic analysis scheme for the measurement of neutrino spectra with the IceCube detector. This scheme is based on regularized unfolding, preceded by an event selection which uses a Minimum Redundancy Maximum Relevance algorithm to select the relevant variables and a random forest for the classification of events. The analysis has been developed using IceCube data from the 59-string configuration of the detector. 27,771 neutrino candidates were detected in 346 days of livetime. A rejection of 99.9999 % of the atmospheric muon background is achieved. The energy spectrum of the atmospheric neutrino flux is obtained using the TRUEE unfolding program. The unfolded spectrum of atmospheric muon neutrinos covers an energy range from 100 GeV to 1 PeV. Compared to the previous measurement using the detector in the 40-string configuration, the analysis presented here, extends the upper end of the atmospheric neutrino spectrum by more than a factor of two, reaching an energy region that has not been previously accessed by spectral measurements.
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| 69. |
- Aartsen, M. G., et al.
(author)
-
Evidence for Astrophysical Muon Neutrinos from the Northern Sky with IceCube
- 2015
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 115:8
-
Journal article (peer-reviewed)abstract
- Results from the IceCube Neutrino Observatory have recently provided compelling evidence for the existence of a high energy astrophysical neutrino flux utilizing a dominantly Southern Hemisphere data set consisting primarily of nu(e) and nu(tau) charged-current and neutral-current ( cascade) neutrino interactions. In the analysis presented here, a data sample of approximately 35 000 muon neutrinos from the Northern sky is extracted from data taken during 659.5 days of live time recorded between May 2010 and May 2012. While this sample is composed primarily of neutrinos produced by cosmic ray interactions in Earth's atmosphere, the highest energy events are inconsistent with a hypothesis of solely terrestrial origin at 3.7 sigma significance. These neutrinos can, however, be explained by an astrophysical flux per neutrino flavor at a level of Phi(E-nu) = 9.9(-3.4)(+3.9) x 10(-19) GeV-1 cm(-2) sr(-1) s(-1) (E-nu/100 TeV)(-2), consistent with IceCube's Southern-Hemisphere-dominated result. Additionally, a fit for an astrophysical flux with an arbitrary spectral index is performed. We find a spectral index of 2.2(-0.2)(+0.2), which is also in good agreement with the Southern Hemisphere result.
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| 70. |
- Aartsen, M. G., et al.
(author)
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Improved limits on dark matter annihilation in the Sun with the 79-string IceCube detector and implications for supersymmetry
- 2016
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In: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; :4
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Journal article (peer-reviewed)abstract
- We present an improved event-level likelihood formalism for including neutrino telescope data in global fits to new physics. We derive limits on spin-dependent dark matter-proton scattering by employing the new formalism in a re-analysis of data from the 79-string IceCube search for dark matter annihilation in the Sun, including explicit energy information for each event. The new analysis excludes a number of models in the weak-scale minimal supersymmetric standard model (MSSM) for the first time. This work is accompanied by the public release of the 79-string IceCube data, as well as an associated computer code for applying the new likelihood to arbitrary dark matter models.
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