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1.
2.
Search for Gamma-Ray Emission from Local Primordial Black Holes with the Fermi Large Area Telescope
Gabrijela Zaharijas, 2018, original scientific article

Found in: ključnih besedah
Summary of found: ... astroparticle physics, black hole physics, methods: data analysis...
Keywords: astroparticle physics, black hole physics, methods: data analysis
Published: 23.08.2018; Views: 989; Downloads: 0
.pdf Fulltext (788,37 KB)

3.
Mass composition of ultra-high energy cosmic rays at the Pierre Auger Observatory
Gašper Kukec Mezek, 2019, doctoral dissertation

Abstract: Cosmic rays with energies above 10^18 eV, usually referred to as ultra-high energy cosmic rays (UHECR), have been a mystery from the moment they have been discovered. Although we have now more information on their extragalactic origin, their direct sources still remain hidden due to deviations caused by galactic magnetic fields. Another mystery, apart from their production sites, is their nature. Their mass composition, still uncertain at these energies, would give us a better understanding on their production, acceleration, propagation and capacity to produce extensive air showers in the Earth's atmosphere. Mass composition studies of UHECR try to determine their nature from the difference in development of their extensive air showers. In this work, observational parameters from the hybrid detection system of the Pierre Auger Observatory are used in a multivariate analysis to obtain the mass composition of UHECR. The multivariate analysis (MVA) approach combines a number of mass composition sensitive variables and tries to improve the separation between different UHECR particle masses. Simulated distributions of different primary particles are fitted to measured observable distributions in order to determine individual elemental fractions of the composition. When including observables from the surface detector, we find a discrepancy in the estimated mass composition between a mixed simulation sample and the Pierre Auger data. Our analysis results from the Pierre Auger data are to a great degree independent on hadronic interaction models. Although they differ at higher primary masses, the different models are more consistent, when combining fractions of oxygen and iron. Compared to previously published results, the systematic uncertainty from hadronic interaction models is roughly four times smaller. Our analysis reports a predominantly heavy composition of UHECR, with more than a 50% fraction of oxygen and iron at low energies. The composition is then becoming heavier with increasing energy, with a fraction of oxygen and iron above 80% at the highest energies.
Found in: ključnih besedah
Summary of found: ... astroparticle physics, ultra-high energy cosmic rays, extensive air...
Keywords: astroparticle physics, ultra-high energy cosmic rays, extensive air showers, mass composition, Pierre Auger Observatory, machine learning, multivariate analysis
Published: 03.04.2019; Views: 1103; Downloads: 62
.pdf Fulltext (17,53 MB)

4.
Mass composition of cosmic rays with energies from 10^17.2 eV to 10^20 eV using surface and fluorescence detectors of the Pierre Auger Observatory
Gašper Kukec Mezek, 2018, published scientific conference contribution

Abstract: Ultra-high-energy cosmic rays (UHECRs) are highly energetic particles with EeV energies, exceeding the capabilities of man-made colliders. They hold information on extreme astrophysical processes that create them and the medium they traverse on their way towards Earth. However, their mass composition at such energies is still unclear, because data interpretation depends on our choice of high energy hadronic interaction models. With its hybrid detection method, the Pierre Auger Observatory has the possibility to detect extensive air showers with an array of surface water-Cherenkov stations (SD) and fluorescence telescopes (FD). We present recent mass composition results from the Pierre Auger Collaboration using observational parameters from SD and FD measurements. Using the full dataset of the Pierre Auger Observatory, implications on composition can be made for energies above 10^17.2 eV.
Found in: ključnih besedah
Summary of found: ... astroparticle physics, ultra-high energy cosmic rays, extensive air...
Keywords: astroparticle physics, ultra-high energy cosmic rays, extensive air showers, mass composition, Pierre Auger Observatory, fluorescence telescopes, water-Cherenkov stations
Published: 24.05.2019; Views: 800; Downloads: 43
.pdf Fulltext (573,00 KB)

5.
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: ključnih besedah
Summary of found: ... astroparticle physics, cosmic rays, anisotropy, large-scale structure of...
Keywords: astroparticle physics, cosmic rays, anisotropy, large-scale structure of universe
Published: 24.04.2020; Views: 447; Downloads: 15
.pdf Fulltext (1,43 MB)

6.
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: ključnih besedah
Summary of found: ... astroparticle physics, cosmic rays, galaxies: starburst, methods: data...
Keywords: astroparticle physics, cosmic rays, galaxies: starburst, methods: data analysis
Published: 27.04.2020; Views: 385; Downloads: 23
.pdf Fulltext (700,72 KB)

7.
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
J. P. Lundquist, R.U. Abbasi, 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.
Found in: ključnih besedah
Summary of found: ...acceleration of particles,astrochemistry, astroparticle physics, cosmic rays, elementary particles, UHECR, composition...
Keywords: acceleration of particles, astrochemistry, astroparticle physics, cosmic rays, elementary particles, UHECR, composition
Published: 27.04.2020; Views: 370; Downloads: 0
.pdf Fulltext (5,52 MB)

8.
The Cosmic Ray Energy Spectrum between 2 PeV and 2 EeV Observed with the TALE Detector in Monocular Mode
J. P. Lundquist, R.U. Abbasi, 2018, original scientific article

Abstract: We report on a measurement of the cosmic ray energy spectrum by the Telescope Array Low-Energy Extension (TALE) air fluorescence detector (FD). The TALE air FD is also sensitive to the Cherenkov light produced by shower particles. Low-energy cosmic rays, in the PeV energy range, are detectable by TALE as Cherenkov events. Using these events, we measure the energy spectrum from a low energy of ~2 PeV to an energy greater than 100 PeV. Above 100 PeV, TALE can detect cosmic rays using air fluorescence. This allows for the extension of the measurement to energies greater than a few EeV. In this paper, we describe the detector, explain the technique, and present results from a measurement of the spectrum using ~1000 hr of observation. The observed spectrum shows a clear steepening near 10^17.1 eV, along with an ankle-like structure at 10^16.2 eV. These features present important constraints on the origin of galactic cosmic rays and on propagation models. The feature at 10^17.1 eV may also mark the end of the galactic cosmic ray flux and the start of the transition to extragalactic sources.
Found in: ključnih besedah
Summary of found: ... astroparticle physics, cosmic rays, UHECR, energy spectrum...
Keywords: astroparticle physics, cosmic rays, UHECR, energy spectrum
Published: 30.04.2020; Views: 359; Downloads: 0
.pdf Fulltext (4,40 MB)

9.
Correlations of the arrival directions of ultra-high energy cosmic ray with extragalactic objects as observed by the telescope array experiment
J. P. Lundquist, T. Abu-Zayyad, 2013, original scientific article

Abstract: We search for correlations between the positions of extragalactic objects and the arrival directions of ultra-high energy cosmic rays (UHECRs) with primary energy E ≥ 40 EeV as observed by the surface detector array of the Telescope Array (TA) experiment during the first 40 months of operation. We examine several public astronomical object catalogs, including the Veron-Cetty and Veron catalog of active galactic nuclei. We count the number of TA events correlated with objects in each catalog as a function of three parameters: the maximum angular separation between a TA event and an object, the minimum energy of the events, and the maximum redshift of the objects. We determine the combination of these parameters that maximizes the correlations, and we calculate the probability of having the same levels of correlations from an isotropic distribution of UHECR arrival directions. No statistically significant correlations are found when penalties for scanning over the above parameters and for searching in several catalogs are taken into account.
Found in: ključnih besedah
Summary of found: ...acceleration of particles, astroparticle physics, cosmic rays...
Keywords: acceleration of particles, astroparticle physics, cosmic rays
Published: 19.05.2020; Views: 300; Downloads: 14
.pdf Fulltext (779,07 KB)

10.
Search for anisotropy of ultrahigh energy cosmic rays with the Telescope Array experiment
J. P. Lundquist, T. Abu-Zayyad, 2012, original scientific article

Abstract: We study the anisotropy of Ultra-High Energy Cosmic Ray (UHECR) events collected by the Telescope Array (TA) detector in the first 40 months of operation. Following earlier studies, we examine event sets with energy thresholds of 10 EeV, 40 EeV, and 57 EeV. We find that the distributions of the events in right ascension and declination are compatible with an isotropic distribution in all three sets. We then compare with previously reported clustering of the UHECR events at small angular scales. No significant clustering is found in the TA data. We then check the events with E > 57 EeV for correlations with nearby active galactic nuclei. No significant correlation is found. Finally, we examine all three sets for correlations with the large-scale structure (LSS) of the universe. We find that the two higher-energy sets are compatible with both an isotropic distribution and the hypothesis that UHECR sources follow the matter distribution of the universe (the LSS hypothesis), while the event set with E > 10 EeV is compatible with isotropy and is not compatible with the LSS hypothesis at 95% CL unless large deflection angles are also assumed. We show that accounting for UHECR deflections in a realistic model of the Galactic magnetic field can make this set compatible with the LSS hypothesis.
Found in: ključnih besedah
Summary of found: ...acceleration of particles, astroparticle physics, cosmic rays, magnetic fields, methods: statistical,...
Keywords: acceleration of particles, astroparticle physics, cosmic rays, magnetic fields, methods: statistical, relativistic processes
Published: 19.05.2020; Views: 302; Downloads: 0
.pdf Fulltext (1,04 MB)

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