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Indications of Intermediate-Scale Anisotropy of Cosmic Rays with Energy Greater Than 57 EeV in the Northern Sky Measured with the Surface Detector of the Telescope Array Experiment
J. P. Lundquist, R.U. Abbasi, 2014, original scientific article

Abstract: We have searched for intermediate-scale anisotropy in the arrival directions of ultrahigh-energy cosmic rays with energies above 57 EeV in the northern sky using data collected over a 5 year period by the surface detector of the Telescope Array experiment. We report on a cluster of events that we call the hotspot, found by oversampling using 20∘-radius circles. The hotspot has a Li-Ma statistical significance of 5.1σ, and is centered at R.A.=146.7∘, Dec.=43.2∘. The position of the hotspot is about 19∘ off of the supergalactic plane. The probability of a cluster of events of 5.1σ significance, appearing by chance in an isotropic cosmic-ray sky, is estimated to be 3.7×10−4 (3.4σ).
Found in: osebi
Keywords: acceleration of particles, cosmic rays, large-scale structure of universe, surveys
Published: 24.04.2020; Views: 525; Downloads: 0
.pdf Fulltext (529,81 KB)

A Northern Sky Survey for Point-Like Sources of EeV Neutral Particles with the Telescope Array Experiment
J. P. Lundquist, R.U. Abbasi, 2015, original scientific article

Abstract: 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.
Found in: osebi
Keywords: acceleration of particles, cosmic rays, surveys
Published: 24.04.2020; Views: 806; Downloads: 0
.pdf Fulltext (1,63 MB)

Radar Sensing of Ultra-High Energy Cosmic Ray Showers
J. P. Lundquist, undergraduate thesis

Abstract: The intent of this paper is to review the history and potential importance of the use of radar techniques in detecting the ionization columns of ultra-high energy cosmic ray showers and give a short overview of a currently planned radar experiment at the Telescope Array. There is much activity in cosmic ray research to study the composition and source locations of this phenomena. Radar would be an important addition to fluorescence and scintillation detection as it theoretically could attain greater volume coverage and nearly the accuracy of fluorescence systems with less infrastructure and much longer running times. The currently estimated mean echo lifetime is on the order of 50 µs for a cosmic ray of energy 10^19 eV. It is shown that a continuous wave bi-directional radar system transmitting in the low-VHF with a large obstruction between receiver and transmitter (such as a mountain or earth curvature), which assures direct transmission is reduced, is the nominal configuration and the planned radar experiment at the Telescope Array satisfies these requirements.
Found in: osebi
Keywords: cosmic rays, radar
Published: 24.04.2020; Views: 476; Downloads: 0
.pdf Fulltext (4,71 MB)

Eenergy Anisotropies of Proton-like Ultra-High Energy Cosmic Rays
J. P. 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.
Found in: osebi
Keywords: cosmic rays, UHECR, composition, anisotropy
Published: 24.04.2020; Views: 494; Downloads: 0
.pdf Fulltext (10,26 MB)

Evidence of Intermediate-scale Energy Spectrum Anisotropy of Cosmic Rays E ≥ 10^19.2 eV with the Telescope Array Surface Detector
J. P. Lundquist, R.U. Abbasi, 2018, original scientific article

Abstract: Evidence for an intermediate-scale energy spectrum anisotropy has been found in the arrival directions of ultra-high energy cosmic rays for energies greater than 10^19.2 eV in the northern hemisphere using 7 years of Telescope Array surface detector data. A relative energy distribution test is done comparing events inside oversampled spherical caps of equal exposure, to those outside, using the Poisson likelihood ratio. The center of maximum significance is at 9h16m, 45°, and has a deficit of events with energies 10^19.2 ≤ E < 10^19.75 eV and an excess for E ≥ 10^19.75 eV. The post-trial probability of this energy anisotropy, appearing by chance anywhere on an isotropic sky, is found by Monte Carlo simulation to be 9 × 10−5 (3.74σ global).
Found in: osebi
Keywords: astroparticle physics, cosmic rays, anisotropy, large-scale structure of universe
Published: 24.04.2020; Views: 559; Downloads: 18
.pdf Fulltext (1,43 MB)

On-orbit performance of the top and bottom counting detectors for the ISS-CREAM experiment on the international space station
J. P. Lundquist, S.C. Kang, 2019, original scientific article

Abstract: The Cosmic Ray Energetics And Mass (CREAM) instrument on the International Space Station (ISS) is an experiment to study origin, propagation, acceleration and elemental composition of cosmic rays. The Top Counting Detector (TCD) and Bottom Counting Detector (BCD) are parts of the detector suite of the ISS-CREAM experiment and are designed to separate electrons and protons for studying electron and gamma-ray physics. In addition, the TCD/BCD provide a redundant trigger to that of the calorimeter and a low energy trigger to the ISS-CREAM instrument. After launching, the TCD/BCD trigger was found to be working well. Also, the TCD/BCD have been stable and their hit positions were confirmed to be well matched with other detectors on board. We present the performance and status of the TCD/BCD in flight.
Found in: osebi
Keywords: ISS-CREAM, CREAM, Cosmic rays, TCD/BCD
Published: 27.04.2020; Views: 417; Downloads: 19
.pdf Fulltext (2,00 MB)

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

Found in: osebi
Keywords: UHECR, Cosmic Rays, Anisotropy
Published: 27.04.2020; Views: 387; Downloads: 0
.pdf Fulltext (6,28 MB)

Mass composition of ultrahigh-energy cosmic rays with the Telescope Array Surface Detector data
J. P. Lundquist, R.U. Abbasi, 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.
Found in: osebi
Keywords: UHECR, Cosmic rays, composition
Published: 27.04.2020; Views: 447; Downloads: 0
.pdf Fulltext (10,07 MB)

Testing a Reported Correlation between Arrival Directions of Ultra-high-energy Cosmic Rays and a Flux Pattern from nearby Starburst Galaxies using Telescope Array Data
J. P. Lundquist, R.U. Abbasi, 2018, original scientific article

Abstract: The Pierre Auger Collaboration (Auger) recently reported a correlation between the arrival directions of cosmic rays with energies above 39 EeV and the flux pattern of 23 nearby starburst galaxies (SBGs). In this Letter, we tested the same hypothesis using cosmic rays detected by the Telescope Array experiment (TA) in the 9-year period from May 2008 to May 2017. Unlike the Auger analysis, we did not optimize the parameter values but kept them fixed to the best-fit values found by Auger, namely 9.7% for the anisotropic fraction of cosmic rays assumed to originate from the SBGs in the list and 12.9◦ for the angular scale of the correlations. The energy threshold we adopted is 43 EeV, corresponding to 39 EeV in Auger when taking into account the energy-scale difference between two experiments. We find that the TA data is compatible with isotropy to within 1.1σ and with the Auger result to within 1.4σ, meaning that it is not capable to discriminate between these two hypotheses.
Found in: osebi
Keywords: astroparticle physics, cosmic rays, galaxies: starburst, methods: data analysis
Published: 27.04.2020; Views: 483; Downloads: 29
.pdf Fulltext (700,72 KB)

Evidence for Declination Dependence of Ultrahigh Energy Cosmic Ray Spectrum in the Northern Hemisphere
J. P. Lundquist, R.U. Abbasi, 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.
Found in: osebi
Keywords: Astrophysics, High Energy Astrophysical Phenomena, UHECR, Cosmic Rays, Anisotropy, Energy Spectrum
Published: 27.04.2020; Views: 502; Downloads: 20
.pdf Fulltext (687,87 KB)

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