1. Large-scale cosmic-ray anisotropies with 19 yr of data from the Pierre Auger ObservatoryA. Abdul Halim, P. Abreu, M. Aglietta, Ingo Allekotte, K. Almeida Cheminant, Jon Paul Lundquist, Shima Ujjani Shivashankara, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2024, original scientific article Abstract: We present results of the measurement of large-scale anisotropies in the arrival directions of
ultra–high-energy cosmic rays detected at the Pierre Auger Observatory during 19 yr of operation,
prior to AugerPrime, the upgrade of the observatory. The 3D dipole amplitude and direction are
reconstructed above 4 EeV in four energy bins. Besides the established dipolar anisotropy in right
ascension above 8 EeV, the Fourier amplitude of the 8–16 EeV energy bin is now also above the 5σ
discovery level. No time variation of the dipole moment above 8 EeV is found, setting an upper limit
to the rate of change of such variations of 0.3% per year at the 95% confidence level. Additionally,
the results for the angular power spectrum are shown, demonstrating no other statistically
significant multipoles. The results for the equatorial dipole component down to 0.03 EeV are
presented, using for the first time a data set obtained with a trigger that has been optimized for
lower energies. Finally, model predictions are discussed and compared with observations, based
on two source emission scenarios obtained in the combined fit of spectrum and composition above 0.6 EeV.
Keywords: ultra–high-energy cosmic rays, UHECRs, UHECR anisotropies, Pierre Auger Observatory, dipolar anisotropy in right ascension, Fourier amplitude analysis, angular power spectrum, equatorial dipole component, UHECR source emission scenarios
Published in RUNG: 26.11.2024; Views: 935; Downloads: 5
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2. Large-scale and multipolar anisotropies of cosmic rays detected at the Pierre Auger Observatory with energies above 4 EeVR. de Almeida, Andrej Filipčič, Jon Paul Lundquist, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2022, published scientific conference contribution Abstract: More than half a century after the discovery of ultra-high energy cosmic rays (UHECRs), their origin is still an open question. The study of anisotropies in the arrival directions of such particles is an essential ingredient to solve this puzzle. We update our previous analysis of large-scale anisotropies observed by the Pierre Auger Observatory using the latest data collected before the AugerPrime upgrade. We select events with zenith angles up to 80 degrees, implying a sky coverage of 85%, and energies above 4 EeV, for which the surface detector of the Observatory is fully efficient. Dipolar and quadrupolar amplitudes are evaluated through a combined Fourier analysis of the event count rate in right ascension and azimuth. The analysis is performed in three energy bins with boundaries at 4, 8, 16 and 32 EeV and two additional cumulative bins with energies above 8 and 32 EeV. The most significant signal is a dipolar modulation in right ascension for energies above 8 EeV, as previously reported, with statistical significance of 6.6σ. Additionally, we report the measurements of the angular power spectrum for the same energy bins with the same dataset.
Keywords: Pierre Auger Observatory, indirect detection, surface detection, ground array, ultra-high energy, cosmic rays, anisotropy, dipole, quadropole, angular power spectrum, inclined showers
Published in RUNG: 03.10.2023; Views: 2481; Downloads: 5
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3. Multi-resolution anisotropy studies of ultrahigh-energy cosmic rays detected at the Pierre Auger ObservatoryA. Aab, Andrej Filipčič, Gašper Kukec Mezek, Ahmed Saleh, Samo Stanič, Marta Trini, Darko Veberič, Serguei Vorobiov, Lili Yang, Danilo Zavrtanik, Marko Zavrtanik, 2017, original scientific article Keywords: Pierre Auger Observatory, ultra-high energy cosmic rays (UHECR), UHECR anisotropies, angular power spectrum, needlet wavelet analysis
Published in RUNG: 23.06.2017; Views: 5600; Downloads: 0
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4. 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: 5989; Downloads: 193
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