1. Arrival directions of the highest-energy cosmic rays detected with the Pierre Auger ObservatoryMarko Zavrtanik, Danilo Zavrtanik, Lili Yang, Serguei Vorobiov, Darko Veberič, Marta Trini, Samo Stanič, Ahmed Saleh, Gašper Kukec Mezek, Andrej Filipčič, Julien Aublin, 2015, published scientific conference contribution Abstract: We present the results of a search for small to intermediate
scale anisotropies in the distribution of arrival directions
of ultra-high energy cosmic rays recorded at the Pierre Auger
Observatory. The data set, gathered in ten years of operation,
includes arrival directions with zenith angles up to 80◦,
and is about three times larger than that used in earlier
studies. We update the test based on correlations with active
galactic nuclei (AGNs) from the Véron-Cetty and Véron catalog,
which does not yield a significant indication of anisotropy
with the present data set. We perform a blind search for
localized excess fluxes and for self-clustering of arrival
directions at angular scales up to 30◦ and for different
energy thresholds between 40 EeV and 80 EeV. We also examine
the correlation of arrival directions with relatively nearby galaxies in the 2MRS catalog, AGNs detected by Swift-BAT,
and a sample of radio galaxies with jets and with the
Centaurus A galaxy. None of the searches shows a statistically
significant evidence of anisotropy. The two largest
departures from isotropy that were found have a post-trial
probability ≈ 1.4%. One is for cosmic rays with energy above
58 EeV that arrive within 15◦ of the direction toward
Centaurus A. The other is for arrival directions within 18◦
of Swift-BAT AGNs closer than 130 Mpc and brighter than
10[sup]44 erg/s, with the same energy threshold. Found in: ključnih besedah Summary of found: ...does not yield a significant indication of anisotropy
with the present data set. We perform... Keywords: ultra-high energy cosmic rays
anisotropy studies
active galactic nuclei
Pierre Auger Observatory Published: 02.03.2016; Views: 4493; Downloads: 226 Fulltext (1,32 MB) |
2. Indications of anisotropy at large angular scales in the arrival directions of cosmic rays detected at the Pierre Auger ObservatoryMarko Zavrtanik, Danilo Zavrtanik, Lili Yang, Serguei Vorobiov, Darko Veberič, Marta Trini, Samo Stanič, Ahmed Saleh, Gašper Kukec Mezek, Andrej Filipčič, Imen Al Samarai, 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. Found in: ključnih besedah Keywords: high-energy cosmic rays
large-scale distribution
anisotropy studies
Pierre Auger Observatory Published: 02.03.2016; Views: 4393; Downloads: 233 Fulltext (862,90 KB) |
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4. Dipolar anisotropy of cosmic rays above 8 EeVMarko Zavrtanik, Danilo Zavrtanik, Lili Yang, Serguei Vorobiov, Marta Trini, Samo Stanič, Ahmed Saleh, Gašper Kukec Mezek, Andrej Filipčič, Oscar Taborda, 2017, published scientific conference contribution Found in: ključnih besedah Keywords: Pierre Auger Observatory, dipolar anisotropy, cosmic rays Published: 16.02.2018; Views: 2647; Downloads: 139 Fulltext (411,21 KB) |
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7. Magnetic anisotropy of strontium ferrite nanoparticlesF. Albertini, C. Sangregorio, Blaž Belec, A. Quesada, T. Schliesch, M. Suara-Muzquiz, Petra Jenuš, M. Albino, M. Petrecca, M. Cabassi, D. Mishra, Cesar De Julian Fernandez, 2019, published scientific conference contribution abstract Found in: ključnih besedah Keywords: hexaferrite, nanoparticles, magnetic anisotropy, SPD Published: 04.06.2019; Views: 2751; Downloads: 0 Fulltext (36,89 MB) |
8. Eenergy Anisotropies of Proton-like Ultra-High Energy Cosmic RaysJon Paul Lundquist, doctoral dissertation Abstract: Evidence of a number of interrelated energy dependent intermediate-scale anisotropies have been found in the arrival directions of proton-like ultra-high energy cosmic rays (UHECR) using 7 years of Telescope Array (TA) data. These are found using analysis techniques that have been developed for this dissertation. Using surface detector (SD) data the reported TA “Hotspot” excess, E≥10^19.75 eV, is found to correspond to a deficit, or “Coldspot,” of events for 10^19.1≤E<10^19.75 eV at 142◦R.A., 40◦ Dec. The global post-trial significance of this Hot/Coldspot event density asymmetry is found to be 5.1σ (p = 1.56 × 10−7). This Hot/Coldspot feature is the combination, at the same location, of an energy spectrum anisotropy with a 3.74σ significance for energies E≥10^19.2 eV and an energy-distance correlation with a 3.34σ significance for energies E≥1019.3 eV. The UHECR Hotspot alone is analyzed using a new kernel density estimation (KDE) anisotropy method and found to have a 3.65σ significance (E≥1019.75 eV). These features suggest energy dependent magnetic deflection of UHECR. The composition of UHECR primary particles is also studied using a new “Quality Factor Analysis” pattern recognition event selection for fluorescence detectors (FD). This minimizes the energy dependence of the resolution of extensive air shower (EAS) Xmax depth. Also, a new statistical method making use of all higher moments than the mean shower depth distribution is developed – as there is large disagreement in between all EAS simulation models. There is also an uncertainty, just as large, for any particular model, given uncertainties in particle interaction parameters extrapolated to much higher energies from Large Hadron Collider (LHC) data. The TA hybrid FD/SD data is found to be statistically compatible with a pure proton composition, though not incompatible with a light mixed composition, for all models of EAS above E≥10^18.4 eV. There is also no statistically significant evidence of the composition getting heavier at the highest energies. The combined information of a proton-like light composition, and anisotropy evidence suggestive of energy dependent magnetic deflection of UHECR, should be useful for informing future source searches and models of intergalactic propagation through magnetic fields. Found in: ključnih besedah Summary of found: ...the same location, of an energy spectrum anisotropy with a 3.74σ significance for energies E≥10^19.2... Keywords: cosmic rays, UHECR, composition, anisotropy Published: 24.04.2020; Views: 2246; Downloads: 0 Fulltext (10,26 MB) |
9. Evidence of Intermediate-scale Energy Spectrum Anisotropy of Cosmic Rays E ≥ 10^19.2 eV with the Telescope Array Surface DetectorJ. P. Lundquist, R.U. Abbasi, 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). Found in: ključnih besedah Keywords: astroparticle physics, cosmic rays, anisotropy, large-scale structure of universe Published: 24.04.2020; Views: 2336; Downloads: 182 Fulltext (1,43 MB) |
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