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11.
Evidence for Declination Dependence of Ultrahigh Energy Cosmic Ray Spectrum in the Northern Hemisphere
J. P. Lundquist, R.U. Abbasi, 2018, drugi članki ali sestavki

Opis: 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.
Najdeno v: ključnih besedah
Povzetek najdenega: ...High Energy Astrophysical Phenomena, UHECR, Cosmic Rays, Anisotropy, Energy Spectrum...
Ključne besede: Astrophysics, High Energy Astrophysical Phenomena, UHECR, Cosmic Rays, Anisotropy, Energy Spectrum
Objavljeno: 27.04.2020; Ogledov: 513; Prenosov: 21
.pdf Polno besedilo (687,87 KB)

12.
Search for Anisotropy in the Ultra High Energy Cosmic Ray Spectrum using the Telescope Array Surface Detector
J. P. Lundquist, R.U. Abbasi, 2017, drugi članki ali sestavki

Opis: 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.
Najdeno v: ključnih besedah
Ključne besede: cosmic radiation: UHE, detector: surface, cosmic radiation: spectrum, cosmic radiation: energy spectrum, deflection: magnetic, numerical calculations: Monte Carlo, anisotropy
Objavljeno: 27.04.2020; Ogledov: 445; Prenosov: 21
.pdf Polno besedilo (169,05 KB)

13.
Supergalactic Structure of Multiplets with the Telescope Array Surface Detector
P. Sokolsky, J. P. Lundquist, 2019, objavljeni znanstveni prispevek na konferenci

Opis: 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.
Najdeno v: ključnih besedah
Povzetek najdenega: ...UHECR, cosmic rays, energy spectrum, anisotropy, large-scale structure, magnetic deflection...
Ključne besede: UHECR, cosmic rays, energy spectrum, anisotropy, large-scale structure, magnetic deflection
Objavljeno: 28.04.2020; Ogledov: 450; Prenosov: 27
.pdf Polno besedilo (1,38 MB)

14.
Evidence of Intermediate-Scale Energy Spectrum Anisotropy in the Northern Hemisphere from Telescope Array
J. P. Lundquist, 2018, objavljeni znanstveni prispevek na konferenci

Opis: 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.
Najdeno v: ključnih besedah
Ključne besede: UHECR, cosmic rays, energy spectrum, anisotropy, magnetic deflection
Objavljeno: 28.04.2020; Ogledov: 435; Prenosov: 19
.pdf Polno besedilo (4,87 MB)

15.
Telescope Array Hot/Coldspot Study – Intermediate Scale Anisotropy
J. P. Lundquist, objavljeni povzetek znanstvenega prispevka na konferenci

Opis: Indications of energy dependent intermediate scale anisotropy has been found in the arrival directions of ultra high energy cosmic rays with energies above 20 EeV in the northern hemisphere, using 7 years of TA surface detector data. The previously reported “hotspot‘” excess for E>57 EeV is found to correspond to a deficit, or “coldspot ”, of events for energies 2057 EeV has a Li Ma statistical significance of 4.62σ, and the deficit for energies 20Najdeno v: ključnih besedah
Ključne besede: cosmic rays, energy spectrum, anisotropy, magnetic deflection
Objavljeno: 28.04.2020; Ogledov: 432; Prenosov: 0
.pdf Polno besedilo (2,25 MB)

16.
Updated Results on the UHECR Hotspot Observed by the Telescope Array Experiment
J. P. Lundquist, K. Kawata, 2019, objavljeni znanstveni prispevek na konferenci

Opis: 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.
Najdeno v: ključnih besedah
Povzetek najdenega: ...Experiment has observed an indication of intermediate-scale anisotropy in the UHECR arrival directions, called the...
Ključne besede: UHECR, cosmic rays, anisotropy
Objavljeno: 28.04.2020; Ogledov: 401; Prenosov: 20
.pdf Polno besedilo (934,91 KB)

17.
TA Anisotropy Summary
J. P. Lundquist, K. Kawata, 2019, objavljeni znanstveni prispevek na konferenci

Opis: The Telescope Array (TA) is the largest ultra-high-energy cosmic-ray (UHECR) detector in the northern hemisphere. It consists of an array of 507 surface detectors (SD) covering a total 700 km^2 and three fluorescence detector stations overlooking the SD array. In this proceedings, we summarize recent results on the search for directional anisotropy of UHECRs using the latest dataset collected by the TA SD array. We obtained hints of the anisotropy of the UHECRs in the northern sky from the various analyses.
Najdeno v: ključnih besedah
Ključne besede: cosmic radiation, UHE detector, fluorescence detector, surface, Telescope Array Experiment, anisotropy, experimental results
Objavljeno: 28.04.2020; Ogledov: 454; Prenosov: 19
.pdf Polno besedilo (1,88 MB)

18.
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, objavljeni znanstveni prispevek na konferenci

Opis: 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.
Najdeno v: ključnih besedah
Povzetek najdenega: ...events over the past years, a large-scale anisotropy at energies above 8 EeV has been...
Ključne besede: UHECR, cosmic rays, anisotropy, Telescope Array, Pierre Auger Observatory
Objavljeno: 28.04.2020; Ogledov: 392; Prenosov: 19
.pdf Polno besedilo (4,92 MB)

19.
Evidence of Intermediate-Scale Energy Spectrum Anisotropy of Cosmic Rays E>10^19.2 eV with the Telescope Array Surface Detector
J. P. Lundquist, objavljeni povzetek znanstvenega prispevka na konferenci

Opis: 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).
Najdeno v: ključnih besedah
Ključne besede: UHECR, cosmic rays, energy spectrum, anisotropy
Objavljeno: 29.04.2020; Ogledov: 395; Prenosov: 21
.pdf Polno besedilo (408,40 KB)

20.
Telescope Array anisotropy summary
J. P. Lundquist, M. Fukushima, 2018, objavljeni znanstveni prispevek na konferenci

Opis: The Telescope Array has accumulated the largest UHECR data set in the Northern hemisphere. We make use of these data to search for large- and small-scale anisotropy of UHECR arrival directions. At small angular scales, we report an update on searches for clustering of events and on correlations with various classes of putative sources. At large angular scales, we revisit, with the new data and with new tests, the localized excess of events known as the TA “hot spot”. We review some other studies of the arrival directions and corresponding implications for the nature of UHECR sources.
Najdeno v: ključnih besedah
Ključne besede: UHECR, cosmic rays, anisotropy
Objavljeno: 29.04.2020; Ogledov: 379; Prenosov: 20
.pdf Polno besedilo (581,87 KB)

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