Repository of University of Nova Gorica

Search the repository
A+ | A- | Help | SLO | ENG

Query: search in
search in
search in
search in
* old and bologna study programme

Options:
  Reset


41 - 50 / 68
First pagePrevious page1234567Next pageLast page
41.
Evidence of Intermediate-Scale Energy Spectrum Anisotropy in the Northern Hemisphere from Telescope Array
Jon Paul Lundquist, 2018, published scientific conference contribution

Abstract: Evidence of an energy dependent intermediate-scale anisotropy has been found in the arrival directions of ultra-high energy cosmic rays in the northern hemisphere, using 7 years of TA surface detector data. The previously reported ``hot spot" excess E ≥ 10^19.75 EeV is found to correspond to a deficit, or ``cold spot," of events for 10^19.2≤ E < 10^19.75 EeV. This feature suggests energy dependent magnetic deflection of cosmic-rays. The global post-trial significance of the energy spectrum deviation is found to be 3.74σ.
Keywords: UHECR, cosmic rays, energy spectrum, anisotropy, magnetic deflection
Published in RUNG: 28.04.2020; Views: 2670; Downloads: 79
.pdf Full text (4,87 MB)

42.
Updated Results on the UHECR Hotspot Observed by the Telescope Array Experiment
K. Kawata, Jon Paul Lundquist, 2019, published scientific conference contribution

Abstract: The Telescope Array Experiment has observed an indication of intermediate-scale anisotropy in the UHECR arrival directions, called the Hotspot, with E>57 EeV around the Ursa Major using the first 5-year data during a period between May 2008 and May 2013 collected by the TA surface detector array. The chance probability of this hotspot in an isotropic cosmic-ray sky was calculated to be 3.4σ (post trial). In this paper, we will report on an update of this result using the 11-year data collected by the TA surface detectors with more than doubled exposure since the first publication.
Keywords: UHECR, cosmic rays, anisotropy
Published in RUNG: 28.04.2020; Views: 2397; Downloads: 80
.pdf Full text (934,91 KB)

43.
Covering the celestial sphere at ultra-high energies: Full-sky cosmic-ray maps beyond the ankle and the flux suppression
J. Biteau, Jon Paul Lundquist, 2019, published scientific conference contribution

Abstract: Despite deflections by Galactic and extragalactic magnetic fields, the distribution of ultra-high energy cosmic rays (UHECRs) over the celestial sphere remains a most promising observable for the identification of their sources. Thanks to a large number of detected events over the past years, a large-scale anisotropy at energies above 8 EeV has been identified, and there are also indications from the Telescope Array and Pierre Auger Collaborations of deviations from isotropy at intermediate angular scales (about 20 degrees) at the highest energies. In this contribution, we map the flux of UHECRs over the full sky at energies beyond each of two major features in the UHECR spectrum – the ankle and the flux suppression, and we derive limits for anisotropy on different angular scales in the two energy regimes. In particular, full-sky coverage enables constraints on low-order multipole moments without assumptions about the strength of higher-order multipoles. Following previous efforts from the two Collaborations, we build full-sky maps accounting for the relative exposure of the arrays and differences in the energy normalizations. The procedure relies on cross-calibrating the UHECR fluxes reconstructed in the declination band around the celestial equator covered by both observatories. We present full-sky maps at energies above ~10 EeV and ~50 EeV, using the largest datasets shared across UHECR collaborations to date. We report on anisotropy searches exploiting full-sky coverage and discuss possible constraints on the distribution of UHECR sources.
Keywords: UHECR, cosmic rays, anisotropy, Telescope Array, Pierre Auger Observatory
Published in RUNG: 28.04.2020; Views: 2482; Downloads: 82
.pdf Full text (4,92 MB)

44.
Supergalactic Structure of Multiplets with the Telescope Array Surface Detector
Jon Paul Lundquist, P. Sokolsky, 2019, published scientific conference contribution

Abstract: Evidence of supergalactic structure of multiplets has been found for ultra-high energy cosmic rays (UHECR) with energies above 10^19 eV using 7 years of data from the Telescope Array (TA) surface detector. The tested hypothesis is that UHECR sources, and intervening magnetic fields, may be correlated with the supergalactic plane, as it is a fit to the average matter density within the GZK horizon. This structure is measured by the average behavior of the strength of intermediate-scale correlations between event energy and position (multiplets). These multiplets are measured in wedge-like shapes on the spherical surface of the fieldof-view to account for uniform and random magnetic fields. The evident structure found is consistent with toy-model simulations of a supergalactic magnetic sheet and the previously published Hot/Coldspot results of TA. The post-trial probability of this feature appearing by chance, on an isotropic sky, is found by Monte Carlo simulation to be ~4.5σ.
Keywords: UHECR, cosmic rays, energy spectrum, anisotropy, large-scale structure, magnetic deflection
Published in RUNG: 28.04.2020; Views: 2734; Downloads: 149
.pdf Full text (1,38 MB)

45.
Supergalactic Structure of Energy-Angle Correlations
Jon Paul Lundquist, P. Sokolsky, 2020, published scientific conference contribution

Abstract: Evidence for the supergalactic structure of multiplets (energy-angle correlations) has previously been shown using ultra-high energy cosmic ray (UHECR) data from Telescope Array (TA) with energies above 10^19 eV. The supergalactic deflection hypothesis (that UHECR sources and intervening magnetic fields are correlated) is measured by the all-sky behavior of the strength of intermediate-scale correlations. The multiplets are measured in spherical surface wedge bins of the field-of-view to account for uniform and random magnetic fields. The structure found is consistent with the previously published energy spectrum anisotropy results of TA and toy-model simulations of a supergalactic magnetic sheet. The 7 year data post-trial significance of this feature appearing by chance, on an isotropic sky, was found by Monte Carlo simulation to be ∼4σ. The analysis has now been applied to 10 years of data.
Keywords: Cosmic rays, UHECR, energy spectrum, magnetic deflection, large-scale structure, supergalactic, multiplets
Published in RUNG: 27.04.2020; Views: 2610; Downloads: 85
.pdf Full text (1,66 MB)

46.
Depth of Ultra High Energy Cosmic Ray Induced Air Shower Maxima Measured by the Telescope Array Black Rock and Long Ridge FADC Fluorescence Detectors and Surface Array in Hybrid Mode
R.U. Abbasi, Jon Paul Lundquist, 2018, original scientific article

Abstract: The Telescope Array (TA) observatory utilizes fluorescence detectors and surface detectors (SDs) to observe air showers produced by ultra high energy cosmic rays in Earth's atmosphere. Cosmic-ray events observed in this way are termed hybrid data. The depth of air shower maximum is related to the mass of the primary particle that generates the shower. This paper reports on shower maxima data collected over 8.5 yr using the Black Rock Mesa and Long Ridge fluorescence detectors in conjunction with the array of SDs. We compare the means and standard deviations of the observed Xmax distributions with Monte Carlo Xmax distributions of unmixed protons, helium, nitrogen, and iron, all generated using the QGSJet II-04 hadronic model. We also perform an unbinned maximum likelihood test of the observed data, which is subjected to variable systematic shifting of the data Xmax distributions to allow us to test the full distributions, and compare them to the Monte Carlo to see which elements are not compatible with the observed data. For all energy bins, QGSJet II-04 protons are found to be compatible with TA hybrid data at the 95% confidence level after some systematic Xmax shifting of the data. Three other QGSJet II-04 elements are found to be compatible using the same test procedure in an energy range limited to the highest energies where data statistics are sparse.
Keywords: acceleration of particles, astrochemistry, astroparticle physics, cosmic rays, elementary particles, UHECR, composition
Published in RUNG: 27.04.2020; Views: 3019; Downloads: 0
This document has many files! More...

47.
Evidence for Declination Dependence of Ultrahigh Energy Cosmic Ray Spectrum in the Northern Hemisphere
R.U. Abbasi, Jon Paul Lundquist, 2018, other component parts

Abstract: The energy of the ultrahigh energy spectral cutoff was measured, integrating over the northern hemisphere sky, by the Telescope Array (TA) collaboration, to be 10^19.78±0.06 eV, in agreement with the High Resolution Fly's Eye (HiRes) experiment, whereas the Pierre Auger experiment, integrating over the southern hemisphere sky, measured the cutoff to be at 10^19.62±0.02 eV. An 11% energy scale difference between the TA and Auger does not account for this difference. However, in comparing the spectra of the Telescope Array and Pierre Auger experiments in the band of declination common to both experiments ( −15.7∘<δ<24.8∘ ) we have found agreement in the energy of the spectral cutoff. While the Auger result is essentially unchanged, the TA cutoff energy has changed to 10^19.59±0.06 eV. In this paper we argue that this is an astrophysical effect.
Keywords: Astrophysics, High Energy Astrophysical Phenomena, UHECR, Cosmic Rays, Anisotropy, Energy Spectrum
Published in RUNG: 27.04.2020; Views: 2863; Downloads: 92
.pdf Full text (687,87 KB)

48.
Mass composition of ultrahigh-energy cosmic rays with the Telescope Array Surface Detector data
R.U. Abbasi, Jon Paul Lundquist, 2019, original scientific article

Abstract: The results on ultrahigh-energy cosmic rays (UHECR) mass composition obtained with the Telescope Array surface detector are presented. The analysis employs the Boosted Decision tree (BDT) multivariate analysis built upon 14 observables related to both the properties of the shower front and the lateral distribution function. The multivariate classifier is trained with Monte-Carlo sets of events induced by the primary protons and iron. An average atomic mass of UHECR is presented for energies 10^18.0–10^20.0 eV. The average atomic mass of primary particles shows no significant energy dependence and corresponds to ⟨lnA⟩=2.0±0.1 (stat.)±0.44(syst.). The result is compared to the mass composition obtained by the Telescope Array with Xmax technique along with the results of other experiments. Possible systematic errors of the method are discussed.
Keywords: UHECR, Cosmic rays, composition
Published in RUNG: 27.04.2020; Views: 2673; Downloads: 0
This document has many files! More...

49.
Full-sky searches for anisotropies in UHECR arrival directions with the Pierre Auger Observatory and the Telescope Array
A. di Matteo, Jon Paul Lundquist, 2020, published scientific conference contribution

Keywords: UHECR, Cosmic Rays, Anisotropy
Published in RUNG: 27.04.2020; Views: 2423; Downloads: 0
This document has many files! More...

50.
Eenergy Anisotropies of Proton-like Ultra-High Energy Cosmic Rays
Jon Paul Lundquist, doctoral dissertation

Abstract: Evidence of a number of interrelated energy dependent intermediate-scale anisotropies have been found in the arrival directions of proton-like ultra-high energy cosmic rays (UHECR) using 7 years of Telescope Array (TA) data. These are found using analysis techniques that have been developed for this dissertation. Using surface detector (SD) data the reported TA “Hotspot” excess, E≥10^19.75 eV, is found to correspond to a deficit, or “Coldspot,” of events for 10^19.1≤E<10^19.75 eV at 142◦R.A., 40◦ Dec. The global post-trial significance of this Hot/Coldspot event density asymmetry is found to be 5.1σ (p = 1.56 × 10−7). This Hot/Coldspot feature is the combination, at the same location, of an energy spectrum anisotropy with a 3.74σ significance for energies E≥10^19.2 eV and an energy-distance correlation with a 3.34σ significance for energies E≥1019.3 eV. The UHECR Hotspot alone is analyzed using a new kernel density estimation (KDE) anisotropy method and found to have a 3.65σ significance (E≥1019.75 eV). These features suggest energy dependent magnetic deflection of UHECR. The composition of UHECR primary particles is also studied using a new “Quality Factor Analysis” pattern recognition event selection for fluorescence detectors (FD). This minimizes the energy dependence of the resolution of extensive air shower (EAS) Xmax depth. Also, a new statistical method making use of all higher moments than the mean shower depth distribution is developed – as there is large disagreement in between all EAS simulation models. There is also an uncertainty, just as large, for any particular model, given uncertainties in particle interaction parameters extrapolated to much higher energies from Large Hadron Collider (LHC) data. The TA hybrid FD/SD data is found to be statistically compatible with a pure proton composition, though not incompatible with a light mixed composition, for all models of EAS above E≥10^18.4 eV. There is also no statistically significant evidence of the composition getting heavier at the highest energies. The combined information of a proton-like light composition, and anisotropy evidence suggestive of energy dependent magnetic deflection of UHECR, should be useful for informing future source searches and models of intergalactic propagation through magnetic fields.
Keywords: cosmic rays, UHECR, composition, anisotropy
Published in RUNG: 24.04.2020; Views: 2820; Downloads: 0
This document has many files! More...

Search done in 0.06 sec.
Back to top