1. Large-scale cosmic-ray anisotropies measured by the Pierre Auger ObservatoryEsteban Roulet, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, published scientific conference contribution Abstract: An update of the measurements of large-scale anisotropies in the arrival directions of ultra high-energy cosmic rays detected at the Pierre Auger Observatory is presented. The established dipolar anisotropy in right ascension has now reached a significance of 6.8σ when considering all energies above 8 EeV and 5.7 σ when only considering energies between 8 and 16 EeV. The 3D dipole amplitude and direction are reconstructed in four different energy bins above 4 EeV. At energies above 8 EeV it points more than 100∘ away from the Galactic centre, providing evidence that the anisotropy observed is of extragalactic origin. An analysis allowing for both dipolar and quadrupolar anisotropies finds qualitatively similar dipole components and no significant quadrupole components. The results for the angular power spectrum are shown, demonstrating that no other statistically significant multipoles are present. The equatorial dipole components are presented down to 0.03 EeV using a trigger which has been optimized for low energies. We find no significant departures from isotropic expectations below 8 EeV, although below 2 EeV the phases appear to be consistently aligned with the right ascension of the Galactic centre. Finally, model predictions based on source emission scenarios obtained in the combined fit of spectrum and composition data above 0.6 EeV are discussed and compared with observations.
Keywords: ultra-high-energy cosmic rays, Pierre Auger Observatory, large scale anisotropies
Published in RUNG: 24.03.2025; Views: 102; Downloads: 0
 Full text (2,76 MB)
This document has many files! More... |
2. 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: 2155; Downloads: 5
Full text (1,95 MB)
This document has many files! More... |
3. 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: 1810; Downloads: 5
Full text (2,66 MB)
This document has many files! More... |
4. 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: 3998; Downloads: 78
Full text (894,55 KB) |
5. Evidence for a Supergalactic Structure of Magnetic Deflection Multiplets of Ultra-High Energy Cosmic RaysR. Abbasi, Jon Paul Lundquist, 2020, original scientific article Abstract: Evidence for a large-scale supergalactic cosmic ray multiplet (arrival directions correlated with energy) structure is reported for ultra-high energy cosmic ray (UHECR) energies above 10^19 eV using seven years of data from the Telescope Array (TA) surface detector and updated to 10 years. Previous energy-position correlation studies have made assumptions regarding magnetic field shapes and strength, and UHECR composition. Here the assumption tested is that, since the supergalactic plane is a fit to the average matter density of the local Large Scale Structure (LSS), UHECR sources and intervening extragalactic magnetic fields are correlated with this plane. This supergalactic deflection hypothesis is tested by the entire field-of-view (FOV) behavior of the strength of intermediate-scale energy-angle correlations. These multiplets are measured in spherical cap section bins (wedges) of the FOV to account for coherent and random magnetic fields. The structure found is consistent with supergalactic deflection, the previously published energy spectrum anisotropy results of TA (the hotspot and coldspot), and toy-model simulations of a supergalactic magnetic sheet. The seven year data post-trial significance of this supergalactic structure of multiplets appearing by chance, on an isotropic sky, is found by Monte Carlo simulation to be 4.19σ. The ten years of data post-trial significance is 4.09σ. Furthermore, the starburst galaxy M82 is shown to be a possible source of the TA Hotspot, and an estimate of the supergalactic magnetic field using UHECR measurements is presented.
Keywords: astroparticle physics, cosmic rays, UHECR, supergalactic plane, multiplets, magnetic deflection, large-scale structure of universe
Published in RUNG: 19.05.2020; Views: 4010; Downloads: 0
This document has many files! More... |
6. 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: 3963; Downloads: 159
Full text (1,38 MB) |
7. 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: 3814; Downloads: 89
Full text (1,66 MB) |
8. Evidence of Intermediate-scale Energy Spectrum Anisotropy of Cosmic Rays E ≥ 10^19.2 eV with the Telescope Array Surface DetectorR.U. Abbasi, Jon Paul Lundquist, 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).
Keywords: astroparticle physics, cosmic rays, anisotropy, large-scale structure of universe
Published in RUNG: 24.04.2020; Views: 4228; Downloads: 204
Full text (1,43 MB) |
9. Indications of Intermediate-Scale Anisotropy of Cosmic Rays with Energy Greater Than 57 EeV in the Northern Sky Measured with the Surface Detector of the Telescope Array ExperimentR.U. Abbasi, Jon Paul Lundquist, 2014, original scientific article Abstract: We have searched for intermediate-scale anisotropy in the arrival directions of ultrahigh-energy cosmic rays with energies above 57 EeV in the northern sky using data collected over a 5 year period by the surface detector of the Telescope Array experiment. We report on a cluster of events that we call the hotspot, found by oversampling using 20∘-radius circles. The hotspot has a Li-Ma statistical significance of 5.1σ, and is centered at R.A.=146.7∘, Dec.=43.2∘. The position of the hotspot is about 19∘ off of the supergalactic plane. The probability of a cluster of events of 5.1σ significance, appearing by chance in an isotropic cosmic-ray sky, is estimated to be 3.7×10−4 (3.4σ).
Keywords: acceleration of particles, cosmic rays, large-scale structure of universe, surveys
Published in RUNG: 24.04.2020; Views: 4316; Downloads: 0
This document has many files! More... |
10. 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: 5745; Downloads: 193
Full text (462,61 KB) |
