261. Indications of Proton-Dominated Cosmic-Ray Composition above 1.6 EeVR.U. Abbasi, Jon Paul Lundquist, 2010, original scientific article Abstract: We report studies of ultrahigh-energy cosmic-ray composition via analysis of depth of air shower maximum (Xmax), for air shower events collected by the High-Resolution Fly’s Eye (HiRes) observatory. The HiRes data are consistent with a constant elongation rate d⟨Xmax⟩/d[log(E)] of 47.9 ± 6.0 (stat) ± 3.2 (syst) g/cm^2/decade for energies between 1.6 and 63 EeV, and are consistent with a predominantly protonic composition of cosmic rays when interpreted via the QGSJET01 and QGSJET-II high-energy hadronic interaction models. These measurements constrain models in which the galactic-to-extragalactic transition is the cause of the energy spectrum ankle at 4×10^18 eV.
Keywords: Cosmic rays, Energy spectrum, Telescope Array, Hybrid, Ultra high energy
Published in RUNG: 27.04.2020; Views: 2748; Downloads: 0
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262. The hybrid energy spectrum of Telescope Array’s Middle Drum Detector and surface arrayR.U. Abbasi, Jon Paul Lundquist, 2015, original scientific article Abstract: The Telescope Array experiment studies ultra high energy cosmic rays using a hybrid detector. Fluorescence telescopes measure the longitudinal development of the extensive air shower generated when a primary cosmic ray particle interacts with the atmosphere. Meanwhile, scintillator detectors measure the lateral distribution of secondary shower particles that hit the ground. The Middle Drum (MD) fluorescence telescope station consists of 14 telescopes from the High Resolution Fly’s Eye (HiRes) experiment, providing a direct link back to the HiRes measurements. Using the scintillator detector data in conjunction with the telescope data improves the geometrical reconstruction of the showers significantly, and hence, provides a more accurate reconstruction of the energy of the primary particle. The Middle Drum hybrid spectrum is presented and compared to that measured by the Middle Drum station in monocular mode. Further, the hybrid data establishes a link between the Middle Drum data and the surface array. A comparison between the Middle Drum hybrid energy spectrum and scintillator Surface Detector (SD) spectrum is also shown.
Keywords: Cosmic rays, Energy spectrum, Telescope Array, Hybrid, Ultra high energy
Published in RUNG: 27.04.2020; Views: 2700; Downloads: 0
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264. The energy spectrum of cosmic rays above 1017.2 eV measured by the fluorescence detectors of the Telescope Array experiment in seven yearsR.U. Abbasi, Jon Paul Lundquist, 2016, original scientific article Abstract: The Telescope Array (TA) experiment is the largest detector to observe ultra-high-energy cosmic rays in the northern hemisphere. The fluorescence detectors at two stations of TA are newly constructed and have now completed seven years of steady operation. One advantage of monocular analysis of the fluorescence detectors is a lower energy threshold for cosmic rays than that of other techniques like stereoscopic observations or coincidences with the surface detector array, allowing the measurement of an energy spectrum covering three orders of magnitude in energy. Analyzing data collected during those seven years, we report the energy spectrum of cosmic rays covering a broad range of energies above 10^17.2eV measured by the fluorescence detectors and a comparison with previously published results.
Keywords: Cosmic rays, Ultra-high energy, Fluorescence detector, Energy spectrum, Ankle, GZK cutoff
Published in RUNG: 27.04.2020; Views: 2780; Downloads: 0
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265. Search for Anisotropy in the Ultra High Energy Cosmic Ray Spectrum using the Telescope Array Surface DetectorR.U. Abbasi, Jon Paul Lundquist, 2017, other component parts Abstract: The Telescope Array (TA) experiment is located in the western desert of Utah, USA, and observes ultra high energy cosmic rays (UHECRs) in the Northern hemisphere. At the highest energies, E>10~EeV, the shape of cosmic ray energy spectrum may carry an imprint of the source density distribution along the line of sight different in different directions of the sky. In this study, we search for such directional variations in the shape of the energy spectrum using events observed with the Telescope Array's surface detector. We divide the TA field of view into two nearly equal-exposure regions: the "on-source" region which we define as ±30∘ of the supergalactic plane containing mostly nearby structures, and the complementary "off-source" region where the sources are further away on average. We compare the UHECR spectra in these regions by fitting them to the broken power law and comparing the resulting parameters. We find that the off-source spectrum has an earlier break at highest energies. The chance probability to obtain such or larger difference in statistically equivalent distributions is estimated as 6.2±1.1×10−4 (3.2σ) by a Monte-Carlo simulation. The observed difference in spectra is in a reasonable quantitative agreement with a simplified model that assumes that the UHECR sources trace the galaxy distribution from the 2MRS catalogue, primary particles are protons and the magnetic deflections can be neglected.
Keywords: cosmic radiation: UHE, detector: surface, cosmic radiation: spectrum, cosmic radiation: energy spectrum, deflection: magnetic, numerical calculations: Monte Carlo, anisotropy
Published in RUNG: 27.04.2020; Views: 2873; Downloads: 98
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266. Evidence for Declination Dependence of Ultrahigh Energy Cosmic Ray Spectrum in the Northern HemisphereR.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: 2991; Downloads: 92
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267. Study of Ultra-High Energy Cosmic Ray composition using Telescope Array’s Middle Drum detector and surface array in hybrid modeR.U. Abbasi, Jon Paul Lundquist, 2015, original scientific article Abstract: Previous measurements of the composition of Ultra-High Energy Cosmic Rays (UHECRs) made by the High Resolution Fly’s Eye (HiRes) and Pierre Auger Observatory (PAO) are seemingly contradictory, but utilize different detection methods, as HiRes was a stereo detector and PAO is a hybrid detector. The five year Telescope Array (TA) Middle Drum hybrid composition measurement is similar in some, but not all, respects in methodology to PAO, and good agreement is evident between data and a light, largely protonic, composition when comparing the measurements to predictions obtained with the QGSJetII-03 and QGSJet-01c models. These models are also in agreement with previous HiRes stereo measurements, confirming the equivalence of the stereo and hybrid methods. The data is incompatible with a pure iron composition, for all models examined, over the available range of energies. The elongation rate and mean values of are in good agreement with Pierre Auger Observatory data. This analysis is presented using two methods: data cuts using simple geometrical variables and a new pattern recognition technique.
Keywords: Ultra-High Energy Cosmic Rays, Cosmic ray composition, Atmospheric fluorescence, Extensive air shower array, Hybrid, Telescope Array
Published in RUNG: 24.04.2020; Views: 3019; Downloads: 0
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268. 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 ObservatoryGašper 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.
Keywords: astroparticle physics, ultra-high energy cosmic rays, extensive air showers, mass composition, Pierre Auger Observatory, fluorescence telescopes, water-Cherenkov stations
Published in RUNG: 24.05.2019; Views: 3401; Downloads: 110
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269. Multi-Messenger Physics With the Pierre Auger ObservatoryKarl-Heinz Kampert, Andrej Filipčič, Gašper Kukec Mezek, Samo Stanič, Marta Trini, Serguei Vorobiov, Lili Yang, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2019, original scientific article Keywords: Pierre Auger Observatory, ultra-high energy cosmic rays, photons, neutrinos, protons, multi-messenger physics and astrophysics
Published in RUNG: 06.05.2019; Views: 3345; Downloads: 107
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270. Monte Carlo studies for the optimisation of the Cherenkov Telescope Array layoutA. Acharyya, Samo Stanič, Serguei Vorobiov, Lili Yang, Danilo Zavrtanik, Marko Zavrtanik, 2019, original scientific article Keywords: very-high energy gamma-ray astronomy, Cherenkov Telescope Array, array layout optimisation, Monte Carlo studies
Published in RUNG: 18.04.2019; Views: 3098; Downloads: 0
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