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21.
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: ključnih besedah
Summary of found: ...The results on ultrahigh-energy cosmic rays ( UHECR) mass composition obtained with the Telescope Array...
Keywords: UHECR, Cosmic rays, composition
Published: 27.04.2020; Views: 1742; Downloads: 0
.pdf Fulltext (10,07 MB)

22.
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: ključnih besedah
Summary of found: ...Astrophysics, High Energy Astrophysical Phenomena, UHECR, Cosmic Rays, Anisotropy, Energy Spectrum...
Keywords: Astrophysics, High Energy Astrophysical Phenomena, UHECR, Cosmic Rays, Anisotropy, Energy Spectrum
Published: 27.04.2020; Views: 1794; Downloads: 60
.pdf Fulltext (687,87 KB)

23.
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: ...ticles,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: 1886; Downloads: 0
.pdf Fulltext (5,52 MB)

24.
Supergalactic Structure of Energy-Angle Correlations
P. Sokolsky, J. P. Lundquist, 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.
Found in: ključnih besedah
Summary of found: ...been shown using ultra-high energy cosmic ray ( UHECR) data from Telescope Array (TA) with energies...
Keywords: Cosmic rays, UHECR, energy spectrum, magnetic deflection, large-scale structure, supergalactic, multiplets
Published: 27.04.2020; Views: 1610; Downloads: 61
.pdf Fulltext (1,66 MB)

25.
Supergalactic Structure of Multiplets with the Telescope Array Surface Detector
P. Sokolsky, J. P. Lundquist, 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.
Found in: ključnih besedah
Summary of found: ...been found for ultra-high energy cosmic rays ( UHECR) with energies above 10^19 eV using 7...
Keywords: UHECR, cosmic rays, energy spectrum, anisotropy, large-scale structure, magnetic deflection
Published: 28.04.2020; Views: 1754; Downloads: 110
.pdf Fulltext (1,38 MB)

26.
Evidence of Intermediate-Scale Energy Spectrum Anisotropy in the Northern Hemisphere from Telescope Array
J. P. 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.
Found in: ključnih besedah
Summary of found: ... UHECR, cosmic rays, energy spectrum, anisotropy, magnetic deflection...
Keywords: UHECR, cosmic rays, energy spectrum, anisotropy, magnetic deflection
Published: 28.04.2020; Views: 1659; Downloads: 56
.pdf Fulltext (4,87 MB)

27.
Updated Results on the UHECR Hotspot Observed by the Telescope Array Experiment
J. P. Lundquist, K. Kawata, 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.
Found in: ključnih besedah
Keywords: UHECR, cosmic rays, anisotropy
Published: 28.04.2020; Views: 1451; Downloads: 56
.pdf Fulltext (934,91 KB)

28.
Covering the celestial sphere at ultra-high energies: Full-sky cosmic-ray maps beyond the ankle and the flux suppression
J. P. Lundquist, J. Biteau, 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.
Found in: ključnih besedah
Summary of found: ...the distribution of ultra-high energy cosmic rays ( UHECRs) over the celestial sphere remains a most...
Keywords: UHECR, cosmic rays, anisotropy, Telescope Array, Pierre Auger Observatory
Published: 28.04.2020; Views: 1569; Downloads: 58
.pdf Fulltext (4,92 MB)

29.
Evidence of Intermediate-Scale Energy Spectrum Anisotropy of Cosmic Rays E>10^19.2 eV with the Telescope Array Surface Detector
J. P. Lundquist, published scientific conference contribution abstract

Abstract: Evidence of an intermediate-scale energy spectrum anisotropy has been found in the arrival directions of ultra-high energy cosmic rays of energies above 10^19.2 eV in the northern hemisphere, using 7 years of Telescope Array (TA) surface detector (SD) 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 139 R.A., 45 Dec., and has a deficit of events with energies 10^19.210^19.75 eV. The post-trial probability of this energy anisotropy, appearing by chance anywhere on an isotropic sky, is found by Monte Carlo (MC) simulation to be 9x10^-5 (3.74 σ_global).
Found in: ključnih besedah
Summary of found: ... UHECR, cosmic rays, energy spectrum, anisotropy...
Keywords: UHECR, cosmic rays, energy spectrum, anisotropy
Published: 29.04.2020; Views: 1621; Downloads: 63
.pdf Fulltext (408,40 KB)

30.
Telescope Array Composition Summary
J. P. Lundquist, W. Hanlon, 2018, published scientific conference contribution

Abstract: Ultra high energy cosmic ray (UHECR) chemical composition is important to resolving questions about the locations of UHECR sources and propagation models. Because composition can only be deduced by a process of statistical inference via the observation of air shower maxima (Xmax), UHECR observatories with large data collection rates must be employed to reduce statistical fluctuations. Telescope Array (TA), the largest cosmic ray observatory in the Northern Hemisphere, is designed to answer the question of UHECR composition, as well as other important features of cosmic ray flux, by combining a large array of over 500 scintillation surface detectors spread over 700 km^2, and three fluorescence detector stations overlooking the array. With eight years of data recorded, results of the measurements of UHECR composition will be presented. UHECR composition is traditionally measured by comparing the first and second moments of the distributions of shower maxima, which evolves with energy, between data and simulations. Reducing statistical fluctuations in the data helps to distinguish between different primary elements in the flux. In the current generation of cosmic ray observatories, UHECR data sets are large enough, and statistical uncertainties are now small enough, that we can safely distinguish between very light primary source flux (i.e., protons) and heavy flux (i.e., iron). Reducing systematic uncertainties is also important though, since large systematic shifts in air shower maxima will influence the interpretation of the data when compared to models. TA therefore employs different methods of measuring Xmax, including stereo air fluorescence, air fluorescence-surface counter hybrid, and a new technique using only surface counters. Updated results of TA hybrid composition among the different methods are presented using up to eight years of data. Agreement among all TA hybrid composition results are shown as well as detailed systematic errors which can be further explored by comparing composition results of the different measurement methods. Comparison of TA Xmax data are compared to different composition models as well.
Found in: ključnih besedah
Summary of found: ...Ultra high energy cosmic ray ( UHECR) chemical composition is important to resolving questions about...
Keywords: UHECR, Cosmic rays, composition
Published: 29.04.2020; Views: 1419; Downloads: 58
.pdf Fulltext (499,33 KB)

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