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Opis: 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.
Ključne besede: cosmic rays, UHECR, composition, anisotropy
Objavljeno v RUNG: 24.04.2020; Ogledov: 2871; Prenosov: 0
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Opis: We report on the search for steady point-like sources of neutral particles around 1018 eV between 2008 and 2013 May with the scintillator SD of the Telescope Array experiment. We found overall no significant point-like excess above 0.5 EeV in the northern sky. Subsequently, we also searched for coincidence with the Fermi bright Galactic sources. No significant coincidence was found within the statistical uncertainty. Hence, we set an upper limit on the neutron flux that corresponds to an averaged flux of 0.07 km−2 yr−1 for E > 1EeV in the northern sky at the 95% confidence level. This is the most stringent flux upper limit in a northern sky survey assuming point-like sources. The upper limit at the 95% confidence level on the neutron flux from Cygnus X-3 is also set to 0.2 km−2 yr−1 for E > 0.5 EeV. This is an order of magnitude lower than previous flux measurements.
Ključne besede: acceleration of particles, cosmic rays, surveys
Objavljeno v RUNG: 24.04.2020; Ogledov: 3569; Prenosov: 0
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