1. Update on the large-scale cosmic-ray anisotropy search at the highest energies by the Telescope Array ExperimentT. Fujii, Jon Paul Lundquist, 2022, published scientific conference contribution Abstract: The study of large-scale anisotropy at the highest energies is essential for understanding the transition from cosmic rays of galactic origin to those of extra-galactic origin, along with the magnetic fields in the galaxy and those beyond. Motivated by a significant detection of the large-scale anisotropy above 8 EeV by the Pierre Auger Observatory (Auger), we had previously reported, using 11 years of Telescope Array (TA) surface array data, a result compatible both with that of Auger, and with an isotropic source distribution [R. U. Abbasi et al., Astrophys. J. Lett. 898, L28 (2020)]. In this contribution, we will show the preliminary updated results using 12 years TA SD data to search for the large-scale anisotropy at the highest energies. Keywords: Telescope Array, indirect detection, surface detection, ground array, ultra-high energy, cosmic rays, anisotropy, large-scale, dipole Published in RUNG: 04.10.2023; Views: 1988; Downloads: 5
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2. The UHECR dipole and quadrupole in the latest data from the original Auger and TA surface detectorsP. Tinyakov, Andrej Filipčič, Jon Paul Lundquist, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2022, published scientific conference contribution Abstract: The sources of ultra-high-energy cosmic rays are still unknown, but assuming standard physics, they are expected to lie within a few hundred megaparsecs from us. Indeed, over cosmological distances cosmic rays lose energy to interactions with background photons, at a rate depending on their mass number and energy and properties of photonuclear interactions and photon backgrounds. The universe is not homogeneous at such scales, hence the distribution of the arrival directions of cosmic rays is expected to reflect the inhomogeneities in the distribution of galaxies; the shorter the energy loss lengths, the stronger the expected anisotropies. Galactic and intergalactic magnetic fields can blur and distort the picture, but the magnitudes of the largest-scale anisotropies, namely the dipole and quadrupole moments, are the most robust to their effects. Measuring them with no bias regardless of any higher-order multipoles is not possible except with full-sky coverage. In this work, we achieve this in three energy ranges (approximately 8-16 EeV, 16-32 EeV, and 32-∞ EeV) by combining surface-detector data collected at the Pierre Auger Observatory until 2020 and at the Telescope Array (TA) until 2019, before the completion of the upgrades of the arrays with new scintillator detectors. We find that the full-sky coverage achieved by combining Auger and TA data reduces the uncertainties on the north-south components of the dipole and quadrupole in half compared to Auger-only results. Keywords: Pierre Auger Observatory, Telescope Array, indirect detection, surface detection, ultra-high energy, cosmic rays, anisotropy, large scale, fully sky coverage, dipole, quadropole Published in RUNG: 29.09.2023; Views: 1664; Downloads: 5
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3. Large-scale anisotropies above 0.03 EeV measured by the Pierre Auger ObservatoryEsteban Roulet, Andrej Filipčič, Gašper Kukec Mezek, Samo Stanič, Marta Trini, Serguei Vorobiov, Lili Yang, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2019, published scientific conference contribution Keywords: ultra-high energy cosmic rays (UHECRs), Pierre Auger Observatory, UHECR arrival directions, large-scale anisotropies Published in RUNG: 24.07.2020; Views: 3815; Downloads: 78
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4. The Energy Scale of the Pierre Auger ObservatoryBruce R. Dawson, Andrej Filipčič, Gašper Kukec Mezek, Samo Stanič, Marta Trini, Serguei Vorobiov, Lili Yang, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2019, published scientific conference contribution Keywords: ultra-high energy cosmic rays, Pierre Auger Observatory, energy scale Published in RUNG: 16.06.2020; Views: 3327; Downloads: 76
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5. Supergalactic Structure of Multiplets with the Telescope Array Surface DetectorJon Paul Lundquist, P. Sokolsky, 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. Keywords: UHECR, cosmic rays, energy spectrum, anisotropy, large-scale structure, magnetic deflection Published in RUNG: 28.04.2020; Views: 3808; Downloads: 159
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6. Supergalactic Structure of Energy-Angle CorrelationsJon Paul Lundquist, P. Sokolsky, 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. Keywords: Cosmic rays, UHECR, energy spectrum, magnetic deflection, large-scale structure, supergalactic, multiplets Published in RUNG: 27.04.2020; Views: 3662; Downloads: 89
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7. A new method to determine the energy scale for high-energy cosmic rays using radio measurements at the Pierre Auger ObservatoryRaphael Krause, Andrej Filipčič, Gašper Kukec Mezek, Ahmed Saleh, Samo Stanič, Marta Trini, Serguei Vorobiov, Lili Yang, Danilo Zavrtanik, Marko Zavrtanik, 2017, published scientific conference contribution Keywords: energy scale, cosmic rays, radio measurements, Pierre Auger Observatory Published in RUNG: 16.02.2018; Views: 4272; Downloads: 149
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8. Large-Scale Distribution of Arrival Directions of Cosmic Rays Detected at the Pierre Auger Observatory and the Telescope Array above 10[sup]19 eVOlivier Deligny, Andrej Filipčič, Gašper Kukec Mezek, Ahmed Saleh, Samo Stanič, Marta Trini, Darko Veberič, Serguei Vorobiov, Lili Yang, Danilo Zavrtanik, Marko Zavrtanik, 2015, published scientific conference contribution Abstract: The large-scale distribution of arrival directions of
high-energy cosmic rays is a key observable in attempts to
understanding their origin. The dipole and quadrupole moments
are of special interest in revealing potential anisotropies.
An unambiguous measurement of these moments as well as
of the full set of spherical harmonic coefficients requires
full-sky coverage. This can be achieved by combining data from
observatories located in both the northern and southern
hemispheres. To this end, a joint analysis using data recorded
at the Pierre Auger Observatory and the Telescope Array above
10[sup]19 eV has been performed. Thanks to the full-sky
coverage, the measurement of the dipole moment reported in
this study does not rely on any assumption on the underlying
flux of cosmic rays. As well, the resolution on the quadrupole
and higher order moments is the best ever obtained. The
resulting multipolar expansion of the flux of cosmic rays
allows a series of anisotropy searches to be performed,
and in particular to report on the first angular power
spectrum of cosmic rays. This allows a comprehensive
description of the angular distribution of cosmic rays
above 10[sup]19 eV. Keywords: Pierre Auger Observatory, Telescope Array, high-energy cosmic rays, large-scale anisotropies, angular power spectrum Published in RUNG: 08.03.2016; Views: 5622; Downloads: 193
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9. Indications of anisotropy at large angular scales in the arrival directions of cosmic rays detected at the Pierre Auger ObservatoryImen Al Samarai, Andrej Filipčič, Gašper Kukec Mezek, Ahmed Saleh, Samo Stanič, Marta Trini, Darko Veberič, Serguei Vorobiov, Lili Yang, Danilo Zavrtanik, Marko Zavrtanik, 2015, published scientific conference contribution Abstract: The large-scale distribution of arrival directions of
high-energy cosmic rays carries major clues to understanding
their origin. The Pierre Auger Collaboration have implemented
different analyses to search for dipolar and quadrupolar
anisotropies in different energy ranges spanning four orders
of magnitude. A common phase ≈270◦ of the first harmonic
modulation in right-ascension was found in adjacent energy intervals below 1 EeV, and another common phase ≈100◦
above 4 EeV. A constancy of phase measurements in ordered
energy intervals originating from a genuine anisotropy is
expected to appear with a smaller number of events than those
needed to achieve significant amplitudes. This led us to
design a prescribed test aimed at establishing whether
this consistency in phases is real at 99% CL. The test required
a total independent exposure of 21,000 km2 sr yr. We report on
the status of this prescription. We also report the results of
the search for a dipole anisotropy for cosmic rays with
energies above 4 EeV using events with zenith angles between
60◦ and 80◦. Compared to previous analyses of events with
zenith angles smaller than 60◦, this extension increases
the size of the data set by 30%, and enlarges the fraction of
exposed sky from 71% to 85%. The largest departure from
isotropy is found in the energy range above 8 EeV, with an
amplitude for the first harmonic in right ascension
r1 = (4.4 ± 1.0) × 10[sup]−2, that has a chance probability
P(≥ r1) = 6.4×10[sup]−5, reinforcing the hint previously
reported with vertical events alone. Keywords: high-energy cosmic rays
large-scale distribution
anisotropy studies
Pierre Auger Observatory Published in RUNG: 02.03.2016; Views: 6298; Downloads: 243
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